class: date: - isaac newton academy 12 in 13 chemistry exam packs...state the type of reaction that...

Seven Kings High School

Alcohols 1

Name: ________________________

Class: ________________________

Date: ________________________

Time: 357 minutes

Marks: 340 marks

Comments:

At minimum complete: Alcohols 1: Question 1 (7 marks) [skeletal formula, oxidation equation, diagram for reflux, anti-bumping granules] Question 2 (15 marks) [fermentation, carbon neutrality, bond enthalpies, calorimetry] Question 8 (15 marks) [isomerism, infrared spectrometry, biofuels, oxidation equation and observation with dichromate] Question 26 (5 marks) [practical question] Total 42 marks.


Q1.Propane-1,2-diol has the structure CH2(OH)CH(OH)CH3. It is used to make polyesters and is one of the main substances in electronic cigarettes (E-cigarettes).

A sample of propane-1,2-diol was refluxed with a large excess of potassium dichromate(VI) and sulfuric acid.

(a) Draw the skeletal formula of propane-1,2-diol.

(1)

(b) Write an equation for this oxidation reaction of propane-1,2-diol under reflux, using [O] to represent the oxidizing agent.

Show the displayed formula of the organic product.

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(c) Draw a labelled diagram to show how you would set up apparatus for refluxing.

(2)

(d) Anti-bumping granules are placed in the flask when refluxing. Suggest why these granules prevent bumping.


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(e) Draw the structure of a different organic product formed when the acidified potassium dichromate(VI) is not in excess.

(1) (Total 7 marks)

Q2. Glucose, produced during photosynthesis in green plants, is a renewable source from which ethanol can be made. Ethanol is a liquid fuel used as a substitute for petrol. The processes involved can be summarised as follows.

Process 1 Photosynthesis in green plants 6CO2 + 6H2O → C6H12O6 + 6O2

Process 2 Fermentation of glucose to form ethanol

Process 3 Complete combustion of ethanol CH3CH2OH + 3O2 → 2CO2 + 3H2O

(a) State three essential conditions for the fermentation of aqueous glucose in Process 2.

Write an equation for the reaction that takes place during this fermentation.

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(b) It has been claimed that there is no net carbon (greenhouse gas) emission to the atmosphere when ethanol made by Process 2 is used as a fuel.

State the term that is used to describe fuels of this type.

Use the equations for Processes 1, 2 and 3 to show why it can be claimed that there is no net emission of carbon-containing greenhouse gases.

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(c) Use the information from the equation for Process 3 above and the mean bond enthalpies from the table below to calculate a value for the enthalpy change for this process.

C–H C–C C–O O–H C=O O=O

Mean bond enthalpy / kJ mol–1

+412 +348 +360 +463 +743 +496

Give one reason why the value calculated from mean bond enthalpies is different from the value given in a data book.

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(d) A student carried out a simple laboratory experiment to measure the enthalpy change for Process 3. The student showed that the temperature of 200 g of water increased by 8.0 °C when 0.46 g of pure ethanol was burned in air and the heat produced was used to warm the water.

Use these results to calculate the value, in kJ mol–1, obtained by the student for this enthalpy change. (The specific heat capacity of water is 4.18 J K–1 g–1)

Give one reason, other than heat loss, why the value obtained from the student’s results is less exothermic than a data book value.

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(Total 15 marks)

Q3. There are seven isomeric carbonyl compounds with the molecular formula C5H10O. The structures and names of some of these isomers are given below.

Structure Name

pentanal

2-methybutanal


2, 2-dimethypropanal

pentan-2-one

(a) (i) Complete the table.

(ii) Two other isomeric carbonyl compounds with the molecular formula C5H10O are not shown in the table. One is an aldehyde and one is a ketone. Draw the structure of each.

isomeric aldehyde isomeric ketone

(4)

(b) Pentanal, CH3CH2CH2CH2CHO, can be oxidised to a carboxylic acid.

(i) Write an equation for this reaction. Use [O] to represent the oxidising agent.

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(ii) Name the carboxylic acid formed in this reaction.

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(c) Pentanal can be formed by the oxidation of an alcohol.

(i) Identify this alcohol.

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(ii) State the class to which this alcohol belongs.

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(Total 8 marks)

Q4. (a) Alcohols can be classed as primary, secondary or tertiary. Draw possible structures for a primary, a secondary and a tertiary alcohol which have the molecular formula C4H8O. Which of the structures you have drawn cannot be oxidised by potassium dichromate in acid solution?

(4)

(b) Explain what is meant by the fingerprint region of an infra-red spectrum. State how it is used to confirm the identity of organic molecules such as the primary, secondary and tertiary alcohols of molecular formula C4H8O.

(2)

(c) Each of the parts below concerns a different pair of isomers. Deduce one possible structural formula for each of the species A to F. Use, where appropriate, the table of infra-red absorption data given on the data sheet.

(i) A and B have the molecular formula C3H8O. A has a broad absorption band at 3300 cm–1 in its infra-red spectrum, but B does not.

(ii) C and D have the molecular formula C5H10. C has a weak absorption band at 1650 cm–1 in its infra-red spectrum, but D does not.

(iii) E and F have the molecular formula C3H6O and both have strong absorption bands at about 1700 cm–1 in their infra-red spectra. E reacts with Tollens’ reagent but F does not.

(6) (Total 12 marks)


Q5.In an investigation of the chemical properties of alcohols, a mixture of ethanol and acidified potassium dichromate(VI) is heated in a conical flask in a water bath.

(a) Explain why a water bath is used to heat the mixture.

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(b) Describe the colour change which would be observed.

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(Total 2 marks)

Q6. Carbon monoxide and hydrogen are used in the manufacture of methanol. An equilibrium is established according to the following equation.

Cu catalyst CO(g) + 2H2(g) CH3OH(g) ∆H = –9l kJ mol–1

(a) Give two features of a reaction at equilibrium.

Feature 1 .....................................................................................................

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Feature 2 ......................................................................................................

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(b) Explain why an increase in temperature causes a decrease in the equilibrium yield of methanol.

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(c) (i) State what is meant by the term catalyst.

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(ii) State the effect, if any, of the copper catalyst on the position of this equilibrium at a fixed temperature.

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(d) Two methods are used to produce carbon monoxide from natural gas. Equations for these two methods are shown below.

Method 1 CH4 + H2O → 2CO + 3H2

Method 2 CH4 + CO2 → 2CO + 2H2

The manufacture of methanol from these sources of carbon monoxide has been described as carbon neutral.

(i) ......................................................................................................................

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(ii) Show how combining the equations from these two methods can lead to the 1:2 mol ratio of carbon monoxide to hydrogen required for this synthesis of methanol.

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(Total 8 marks)


Q7.Consider the following scheme of reactions.

(a) State the type of structural isomerism shown by propanal and propanone.

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(b) A chemical test can be used to distinguish between separate samples of propanal and propanone.

Identify a suitable reagent for the test. State what you would observe with propanal and with propanone.

Test reagent...................................................................................................

Observation with propanal............................................................................

Observation with propanone......................................................................... (3)

(c) State the structural feature of propanal and propanone which can be identified from their infrared spectra by absorptions at approximately 1720 cm–1.

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(d) The reaction of chlorine with propane is similar to the reaction of chlorine with methane.

(i) Name the type of mechanism in the reaction of chlorine with methane.


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(ii) Write an equation for each of the following steps in the mechanism for the reaction of chlorine with propane to form l-chloropropane (CH3CH2CH2Cl).

Initiation step

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First propagation step

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Second propagation step

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A termination step to form a molecule with the empirical formula C3H7

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(e) High resolution mass spectrometry of a sample of propane indicated that it was contaminated with traces of carbon dioxide.

Use the data in the table to show how precise Mr values can be used to prove that thesample contains both of these gases.

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(Total 12 marks)


Q8. There are four isomeric alcohols with the molecular formula C4H10O

(a) Two of these are butan-l-ol (CH3CH2CH2CH2OH) and butan-2-ol. The other two isomers are alcohol X and alcohol Y.

Draw the displayed formula for butan-2-ol.

Alcohol X does not react with acidified potassium dichromate(VI) solution. Give the structure of alcohol X.

Name the fourth isomer, alcohol Y.

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(b) The infrared spectrum of one of these isomeric alcohols is given below.

Identify one feature of the infrared spectrum which supports the fact that this is an alcohol. You may find it helpful to refer to Table 1 on the Data Sheet.

Explain how infrared spectroscopy can be used to identify this isomeric alcohol.


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(c) British scientists have used bacteria to ferment glucose and produce the biofuel butan-1-ol.

Write an equation for the fermentation of glucose (C6H12O6) to form butan-1-ol, carbon dioxide and water only.

State one condition necessary to ensure the complete combustion of a fuel in air.

Write an equation for the complete combustion of butan-1-ol and state why it can be described as a biofuel.

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(d) Butan-1-ol reacts with acidified potassium dichromate(VI) solution to produce two organic compounds.

State the class of alcohols to which butan-1-ol belongs.

Draw the displayed formula for both of the organic products.

State the type of reaction that occurs and the change in colour of the potassium dichromate(VI) solution.

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(Total 15 marks)

Q9.Ethanol can be oxidised slowly to ethanal. State how a sample of ethanol could be tested to confirm the presence of ethanal. State what you would observe.

Test .........................................................................................................................

Observation ............................................................................................................ (Total 2 marks)

Q10.Ethanal is prepared by heating ethanol with potassium dichromate(VI) in the presence of sulfuric acid. Figures 1 and 2 show two possible ways of heating this reaction mixture.

Figure 1 Figure 2


State which arrangement would not be suitable for the preparation of ethanal. Explain your answer.

Arrangement ...........................................................................................................

Explanation .............................................................................................................

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Q11.Some alcohols can be oxidised by an acidified solution of potassium dichromate(Vl). Aldehydes can be oxidised by Tollens’ reagent or by Fehling’s solution.

An unknown pure liquid A contains only a single alcohol. Outline a simple procedure to allow you to determine whether A is a primary, a secondary or a tertiary alcohol.

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Q12. A student devised an experiment to investigate the enthalpies of combustion of some alcohols. The student chose the following series of primary alcohols.

Name Formula

Methanol CH3OH

Ethanol CH3CH2OH

Propan-1-ol CH3CH2CH2OH

Butan-1-ol CH3CH2CH2CH2OH

Pentan-1-ol CH3CH2CH2CH2CH2OH

Alcohol X CH3CH2CH2CH2CH2CH2OH

Heptan-1-ol CH3CH2CH2CH2CH2CH2CH2OH

(a) (i) Name alcohol X.

............................................................................................................. (1)

(ii) State the general name of the type of series shown by these primary alcohols.

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(iii) Draw the displayed formula of the position isomer of butan-1-ol.


(1)

(iv) Using [O] to represent the oxidising agent, write an equation for the oxidation of butan-1-ol to form an aldehyde.

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(v) Draw the displayed formula of a functional group isomer of this aldehyde.

(1)

(b) The student carried out a laboratory experiment to determine the enthalpy change when a sample of butan-1-ol was burned. The student found that the temperature of 175 g of water increased by 8.0 °C when 5.00 × 10–3 mol of pure butan-1-ol was burned in air and the heat produced was used to warm the water.

Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of butan-1-ol is burned. (The specific heat capacity of water is 4.18 J K–1 g–1)

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(c) (i) Give the meaning of the term standard enthalpy of combustion.

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(ii) Use the standard enthalpy of formation data from the table and the equation for the combustion of butan-1-ol to calculate a value for the standard enthalpy of combustion of butan-1-ol.

CH3CH2CH2CH2OH(l) O2(g) CO2(g) H2O(l)

ΔHfο / kJ mol–1 –327 0 –394 –286

CH3CH2CH2CH2OH(l) + 6O2(g) 4CO2(g) + 5H2O(l)

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(d) The student repeated the experiment described in part (b) and obtained an experimental value for the enthalpy of combustion for each alcohol in this series. These experimental values were then compared with calculated values from standard enthalpies of formation, as shown in the graph below.


(i) In terms of bonds broken and bonds formed, explain why the calculated values of enthalpies of combustion of these alcohols, when plotted against Mr, follow a straight line.

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(ii) Give two reasons why the experimental values obtained by the student are lower than the calculated values using the enthalpy of formation data.

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(Total 18 marks)

Q13. Sulfuric acid is an important chemical in many industrial and laboratory reactions. Consider the following three reactions involving sulfuric acid.

Reaction 1 Mg(OH)2 + H2SO4 → MgSO4 + 2H2O


Reaction 2 The reaction of solid sodium bromide with concentrated sulfuric acid

Reaction 3 H2C=CH2 + H2O CH3CH2OH

(a) Give a use for magnesium hydroxide in medicine.

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(b) Sulfuric acid behaves as an oxidising agent in Reaction 2.

(i) In terms of electrons, state the meaning of the term oxidising agent.

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(ii) Give the formula of the oxidation product that is formed from sodium bromide in Reaction 2.

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(iii) Deduce the half-equation for the reduction of H2SO4 to SO2 in Reaction 2.

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(c) The formation of ethanol in Reaction 3 uses concentrated sulfuric acid and proceeds in two stages according to the following equations.

Stage 1 H2C=CH2 + H2SO4 → CH3CH2OSO2OH

Stage 2 CH3CH2OSO2OH + H2O → CH3CH2OH + H2SO4

(i) State the overall role of sulfuric acid in Reaction 3.

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(ii) Outline a mechanism for Stage 1 of this reaction.


(4)

(iii) State the class of alcohols to which ethanol belongs.

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(iv) Draw the displayed formula of the carboxylic acid formed when ethanol is oxidised by an excess of acidified potassium dichromate(VI) solution.

(1)

(Total 11 marks)

Q14. The following pairs of compounds can be distinguished by observing what happens in test-tube reactions. For each pair, give a suitable aqueous reagent that could be added separately to each compound. Describe what you would observe in each case.

(a) NaF(aq) and NaCl(aq)

Reagent ......................................................................................................

Observation with NaF(aq) ...........................................................................

Observation with NaCl(aq) .......................................................................... (3)


(b) BaCl2(aq) and MgCl2(aq)

Reagent .......................................................................................................

Observation with BaCl2(aq) ..........................................................................

Observation with MgCl2(aq) .......................................................................... (3)

(c) AgCl(s) and AgI(s)

Reagent .......................................................................................................

Observation with AgCl(s) .............................................................................

Observation with AgI(s) ............................................................................... (3)

(d) Butan-2-ol(l) and 2-methylpropan-2-ol(l)

Reagent …...................................................................................................

Observation with butan-2-ol(l) .....................................................................

Observation with 2-methylpropan-2-ol(l) ..................................................... (3)

(Total 12 marks)

Q15.Three different ways of producing ethanol are shown below.


(a) Reaction 1 produces a 15% aqueous solution of ethanol. It is claimed that the ethanol produced in this way is a carbon-neutral biofuel.

Write an equation for Reaction 1 and name the process.

Write an equation for the complete combustion of ethanol.

Explain why the ethanol produced by this process may not be a carbon-neutral biofuel.

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(b) Give a reagent and conditions for Reaction 2.

CH3CH2Br

CH3CH2OH

Name and outline a mechanism for Reaction 2.

Suggest one reason, other than safety, why this method is not used in industry to


make ethanol.

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(c) Reaction 3 is used in industry.

H2C =CH2

CH3CH2OH

Identify a suitable catalyst for Reaction 3.

Identify the type of reaction.

Give two conditions, in addition to the presence of a catalyst, necessary for Reaction 3 to produce a high yield of ethanol.

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(Total 15 marks)

Q16.(a) Propanoic acid can be made from propan-1-ol by oxidation using acidified potassium dichromate(VI). Propanal is formed as an intermediate during this oxidation.

(i) State the colour of the chromium species after the potassium dichromate(VI) has reacted.

............................................................................................................... (1)

(ii) Describe the experimental conditions and the practical method used to ensure that the acid is obtained in a high yield. Draw a diagram of the assembled apparatus you would use.

Conditions .............................................................................................

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Apparatus


(4)

(iii) Describe the different experimental conditions necessary to produce propanal in high yield rather than propanoic acid.

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(b) Propan-1-ol is a volatile, flammable liquid. Give one safety precaution that should be used during the reaction to minimise this hazard.

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(c) A student followed the progress of the oxidation of propan-1-ol to propanoic acid by extracting the organic compounds from one sample of reaction mixture.

(i) Give a chemical reagent which would enable the student to confirm the presence of propanal in the extracted compounds. State what you would observe when propanal reacts with this reagent.

Reagent .............................................................................................

Observation .......................................................................................

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(ii) Give a chemical reagent that would enable the student to confirm the presence of propanoic acid in the extracted compounds. State what you would observe when propanoic acid reacts with this reagent.

Reagent .............................................................................................

Observation .......................................................................................

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(d) Predict which one of the compounds, propan-1-ol, propanal and propanoic acid will have the highest boiling point. Explain your answer.

Prediction ....................................................................................................

Explanation ..................................................................................................

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(Total 15 marks)

Q17. The table below shows the structures of three isomers with the molecular formula C5H10O

Isomer 1

(E)-pent-3-en-2-ol

Isomer 2

pentanal

Isomer 3

(a) Complete the table by naming Isomer 3. (1)


(b) State the type of structural isomerism shown by these three isomers.

..................................................................................................................... (1)

(c) The compound (Z)-pent-3-en-2-ol is a stereoisomer of (E)-pent-3-en-2-ol.

(i) Draw the structure of (Z)-pent-3-en-2-ol.

(1)

(ii) Identify the feature of the double bond in (E)-pent-3-en-2-ol and that in (Z)-pent-3-en-2-ol that causes these two compounds to be stereoisomers.

............................................................................................................. (1)

(d) A chemical test can be used to distinguish between separate samples of Isomer 2 and Isomer 3. Identify a suitable reagent for the test. State what you would observe with Isomer 2 and with Isomer 3.

Test reagent ...............................................................................................

Observation with Isomer 2...........................................................................

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Observation with Isomer 3............................................................................

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(e) The following is the infrared spectrum of one of the isomers 1, 2 or 3.


(i) Deduce which of the isomers (1, 2 or 3) would give this infrared spectrum. You may find it helpful to refer to Table 1 on the Data Sheet.

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(ii) Identify two features of the infrared spectrum that support your deduction. In each case, identify the functional group responsible.

Feature 1 and functional group ...........................................................

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Feature 2 and functional group ...........................................................

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(Total 10 marks)

Q18.Baking powder contains sodium hydrogencarbonate and an acid or a mixture of acids. One acid that may be in baking powder is 2,3-dihydroxybutanedioic acid. This has the molecular formula C4H6O6 and it is often referred to as tartaric acid.

(a) Draw the structural formula of tartaric acid.


(1)

(b) Write an equation for the reaction of tartaric acid (C4H6O6) with sodium hydrogencarbonate to form a salt, carbon dioxide and water.

........................................................................................................................ (1)

(c) Substances that contain carbonate or hydrogencarbonate ions can be used to confirm the presence of an acid.

Identify one other substance that could be used to confirm the presence of acid groups in tartaric acid. State the observation you would make when this other substance is added to an aqueous solution of tartaric acid.

Substance ......................................................................................................

Observation ....................................................................................................

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(d) It is known that tartaric acid contains alcohol and carboxylic acid functional groups only. A test can be used to show that tartaric acid contains secondary alcohol groups, not tertiary alcohol groups.

(i) Identify a reagent for this test and state the observation you would make for each type of alcohol.

Reagent ................................................................................................

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Observation for secondary alcohol .......................................................

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Observation for tertiary alcohol .............................................................

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(ii) Suggest why this test cannot be used to distinguish between a primary alcohol and a secondary alcohol.

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(e) Baking powder usually contains starch. Starch is added to absorb any water vapour that may come into contact with the baking powder when the container is opened.

Deduce a reason why this water vapour needs to be absorbed.

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(f) Sodium hydrogencarbonate in baking powder forms carbon dioxide during the production of bread and cakes.

Suggest one advantage of having an acid in baking powder.

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(g) Safety information indicates that tartaric acid and its salts can act as muscle toxins. These can cause paralysis and possible death.

Suggest one reason why the use of tartaric acid in baking powder is not a hazard to health.

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(Total 11 marks)


Q19.The following instructions are from an experimental procedure for the preparation of cyclohexene from cyclohexanol and concentrated phosphoric acid. Read these instructions and answer the questions that follow.

1 Place 25 cm3 of cyclohexanol into a round-bottomed flask with some porous pot to act as anti-bumping granules. Add 10 cm3 of concentrated phosphoric acid carefully while shaking the flask. Cool the flask under the tap if it gets too hot. Make sure the reagents are thoroughly mixed.

2 Set up an apparatus for simple distillation using this flask.

3 Warm the flask, gently at first, for about 15 minutes. Then increase the heating so that cyclohexene begins to distil over. Collect the fraction that distils below 95 °C.

(a) State the purpose of the anti-bumping granules.

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(b) Name the part of the distillation apparatus where cyclohexene vapour is changed back into a liquid. Draw a simple diagram of this part of the apparatus.

Name .............................................................................................................

Diagram

(2)

(Total 3 marks)


Q20.The reaction of butane-1,4-diol with butanedioic acid produces the polymer PBS used in biodegradable packaging and disposable cutlery. Butanedioic acid is produced by two different processes.

Process 1

• Aqueous sodium hydroxide reacts with 1,4-dibromobutane to make butane-1,4-diol.

• Butane-1,4-diol is oxidised to butanedioic acid.

Process 2

• Glucose reacts with carbon dioxide in the presence of microorganisms to produce butanedioic acid directly.

• The carbon dioxide used in this process is obtained from a local factory that produces bioethanol.

(a) Deduce one safety reason and one environmental reason why Process 2 is preferred to Process 1.

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(b) (i) Name and outline a mechanism for the following reaction that occurs in Process 1.


BrCH2CH2CH2CH2

Br + NaOH BrCH2CH2CH2CH2

OH + NaBr

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(3)

(ii) The infrared spectra shown are those of three compounds.

Compound A 1,4-dibromobutaneCompound B butane-1,4-diol Compound C butanedioic acid

Identify the compound responsible for each spectrum by writing the correct letter, A, B or C, in the box next to each spectrum. You may find it helpful to refer to Table 1 on the Data Sheet.


(3)

(c) In the production of bioethanol, glucose (C6H12O6) is converted into a dilute aqueous solution of ethanol and carbon dioxide.

Give the name of this process and state three essential conditions necessary to produce a good yield of ethanol.

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(d) State the class of alcohols to which the diol butane-1,4-diol belongs.

Identify a suitable reagent or combination of reagents for the conversion of butane-1,4-diol into butanedioic acid (HOOCCH2CH2COOH).

Write an equation for this oxidation reaction using [O] to represent the oxidising agent.

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(Total 15 marks)

Q21.Glucose is an organic molecule. Glucose can exist in different forms in aqueous solution.

(a) In aqueous solution, some glucose molecules have the following structure.

(i) Deduce the empirical formula of glucose.

............................................................................................................... (1)

(ii) Consider the infrared spectrum of solid glucose.


Wavenumber / cm–1

State why it is possible to suggest that in the solid state very few molecules have the structure shown. You may find it helpful to refer to Table 1 on the Data Sheet.

...............................................................................................................

............................................................................................................... (1)

(b) In the absence of oxygen, an aqueous solution of glucose can be fermented to produce ethanol for use in alcoholic drinks.

Write an equation for this fermentation reaction. Give two other essential conditions for the production of ethanol in this fermentation.

Equation

........................................................................................................................

Condition 1 ......................................................................................................

Condition 2 ...................................................................................................... (3)

(c) Any ethanol present in the breath of a drinker can be detected by using a breathalyser. The ethanol is converted into ethanoic acid. The breathalyser has negative and positive electrodes. A current is measured and displayed in terms of alcohol content.

The overall redox equation is as follows

CH3CH2OH(I) + O2(g) CH3COOH(I) + H2O(I)

(i) Draw the displayed formula for ethanoic acid.


(1)

(ii) Deduce a half-equation for the reduction of atmospheric oxygen to water in acidic solution at one electrode of the breathalyser.

............................................................................................................... (1)

(iii) Deduce a half-equation for the oxidation of ethanol in water to ethanoic acid at the other electrode of the breathalyser.

............................................................................................................... (1)

(iv) The earliest breathalysers used laboratory chemicals to oxidise the ethanol to ethanoic acid. Detection was by a colour change.

Identify a reagent or combination of reagents that you would use in the laboratory to oxidise ethanol to ethanoic acid. State the colour change that you would expect to see.

Reagent or combination of reagents .......................................................

Colour change ......................................................................................... (2)

(d) The fermentation of glucose from crops is the main method for the production of ethanol. The product is called bioethanol. The European Union has declared that bioethanol is carbon-neutral.

(i) State the meaning of the term carbon-neutral.

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(Extra space) .......................................................................................

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(ii) Other than carbon-neutrality, state the main advantage of the use of glucose from crops as the raw material for the production of ethanol.

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(iii) Give one disadvantage of the use of crops for the production of ethanol.

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(Total 13 marks)

Q22.(a) Propanone can be formed when glucose comes into contact with bacteria in the absence of air.

(i) Balance the following equation for this reaction of glucose to form propanone, carbon dioxide and water.

.......C6H12O6 .......CH3COCH3 + .......CO2 + .......H2O (1)

(ii) Deduce the role of the bacteria in this reaction.

............................................................................................................... (1)

(b) Propanone is also formed by the oxidation of propan−2−ol.

(i) Write an equation for this reaction using [O] to represent the oxidising agent.

............................................................................................................... (1)

(ii) State the class of alcohols to which propan−2−ol belongs.

............................................................................................................... (1)


(c) A student determined a value for the enthalpy change when a sample of propanone was burned. The heat produced was used to warm some water in a copper calorimeter. The student found that the temperature of 150 g of water increased by 8.0 °C when 4.50 × 10−3 mol of pure propanone was burned in air.

Use the student’s results to calculate a value, in kJ mol−1, for the enthalpy change when one mole of propanone is burned. (The specific heat capacity of water is 4.18 J K−1 g−1)

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(d) Define the term standard enthalpy of combustion.

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(e) Use the mean bond enthalpy data in the table and the equation given below the table to calculate a value for the standard enthalpy change when gaseous propanone is burned.


C−H C−C C−O O−H C=O O=O

Mean bond enthalpy / kJ mol−1

412 348 360 463 805 496

CH3COCH3(g) + 4O2(g) 3CO2(g) + 3H2O(g)

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(f) Suggest two reasons why the value obtained by the student in part (c) is different from the value calculated in part (e).

Reason 1 ........................................................................................................

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Reason 2 ........................................................................................................

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(Total 15 marks)

Q23.In each of the following questions, you should draw the structure of the compound in the space provided.

(a) Draw the structure of the alkene that would form 1,2-dibromo-3-methylbutane when reacted with bromine.


(1)

(b) Draw the structure of the alcohol with molecular formula C4H10O that is resistant to oxidation by acidified potassium dichromate(VI).

(1)

(c) Draw the structure of the alkene that has a peak, due to its molecular ion, at m/z = 42 in its mass spectrum.

(1)

(d) Draw the structure of the organic product with Mr = 73, made from the reaction between 2-bromobutane and ammonia.

(1)

(Total 4 marks)

Q24.A sample of 2-methylpropan-2-ol was contaminated with butan-2-ol. The student separated the two alcohols using chromatography.

Identify a reagent or combination of reagents that the student could use to distinguish between these alcohols. State what would be observed for each alcohol.

Reagent(s) ..............................................................................................................

Observation with 2-methylpropan-2-ol ....................................................................


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Observation with butan-2-ol ....................................................................................

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Q25.Ethanoic acid, propyl ethanoate and propan-1-ol are all colourless liquids. Esters do not give a positive result with any of the usual tests for functional groups.

State how you could use chemical tests to show the presence of ethanoic acid and propan-1-ol in a mixture of the acid, the alcohol and the ester.

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Q26.This question concerns the oxidation of a primary alcohol.

The experiment was carried out using the distillation apparatus shown in the diagram. The oxidation product was distilled off as soon as it was formed.


(a) Suggest the identity of reagent P.

........................................................................................................................ (1)

(b) State the chemical change that causes the solution in the flask to appear green at the end of the reaction.

........................................................................................................................ (1)

(c) Give one reason why using a water bath is better than direct heating with a Bunsen burner.

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........................................................................................................................ (1)

(d) Suggest a reagent that could be used to confirm the presence of an aldehyde in the distillate. State the observation you would expect to make if an aldehyde were present.


Reagent ..........................................................................................................

Observation .................................................................................................... (2)

(Total 5 marks)

Q27.Ethanol is an important fuel.

(a) A dilute aqueous solution of ethanol can be produced by the fermentation of an aqueous solution of glucose. It is claimed that the ethanol obtained from this solution is a carbon-neutral biofuel.

Write an equation for this fermentation reaction.

Give two other essential conditions for this reaction to produce a good yield of ethanol.

Name a process used to produce a much more concentrated solution of ethanol from a dilute aqueous solution.

State the meaning of the term carbon-neutral in the context of this biofuel.

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(b) A student carried out a laboratory experiment to determine the enthalpy change when a sample of ethanol was burned. The heat produced was used to warm some water in a copper calorimeter. The student found that the temperature of 75.0 g of water increased by 5.50 °C when 2.40 × 10–3 mol of pure ethanol was burned in air.

Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of ethanol is burned. (The specific heat capacity of water is 4.18 J K–1 g–1)

Deduce two reasons why the student’s value for the standard enthalpy of combustion of ethanol is different from a Data Book value of –1279 kJ mol–1.

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(c) Mean bond enthalpies can be used to calculate enthalpies of reaction.

(i) Give the meaning of the term mean bond enthalpy.

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(2)

(ii) Consider the mean bond enthalpy data in the following table.

C—H C—C C—O O=O C=O O—H

Mean bond enthalpy / kJ mol–1

412 348 360 to be calculated 805 463

Use the data in the table above and the equation shown to calculate a value for the bond enthalpy for the O=O double bond in an oxygen molecule.

CH3CH2OH(g) + 3O2(g) 2CO2(g) + 3H2O(g) ΔH = –1279 kJ mol–1

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(Total 15 marks)

Q28.Alcohol A (CH3)2CHCH(OH)CH3 undergoes reactions separately with acidified potassium dichromate(VI) and with concentrated sulfuric acid.

(a) Deduce the IUPAC name for alcohol A.

........................................................................................................................ (1)

(b) Draw the structure of the organic product, B, formed when A is oxidised in the reaction with acidified potassium dichromate(VI).


(1)

(c) Two isomeric alkenes, C and D, are formed when A is dehydrated in the reaction with concentrated sulfuric acid.

Name the mechanism for this dehydration reaction.

........................................................................................................................ (1)

(d) Draw the structure of each isomer.

Isomer C Isomer D

(2)

(e) Name the type of structural isomerism shown by C and D.

........................................................................................................................ (1)

(f) List alcohol A, product B and isomer C in order of increasing boiling point.

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(g) Draw the structure of the isomer of A that is not oxidised by acidified potassium dichromate(VI).


(1)

(h) Draw the structure of the isomer of A that cannot be dehydrated to form an alkene by reaction with concentrated sulfuric acid.

(1)

(Total 9 marks)

Q29.Ethanol can be oxidised by acidified potassium dichromate(VI) to ethanoic acid in a two-step process.

ethanol ethanal ethanoic acid

(a) In order to ensure that the oxidation to ethanoic acid is complete, the reaction is carried out under reflux.

Describe what happens when a reaction mixture is refluxed and why it is necessary, in this case, for complete oxidation to ethanoic acid.

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(b) Write a half-equation for the overall oxidation of ethanol into ethanoic acid.

........................................................................................................................ (1)

(c) The boiling points of the organic compounds in a reaction mixture are shown in the following table.

Compound ethanol ethanal ethanoic acid

Boiling point / °C 78 21 118

Use these data to describe how you would obtain a sample of ethanal from a mixture of these three compounds. Include in your answer a description of the apparatus you would use and how you would minimise the loss of ethanal. Your description of the apparatus can be either a description in words or a labelled sketch.

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(d) Use your knowledge of structure and bonding to explain why it is possible to separate ethanal in this way.

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(e) A student obtained a sample of a liquid using the apparatus in part (c).

Describe how the student could use chemical tests to confirm that the liquid contained ethanal and did not contain ethanoic acid.

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(Total 16 marks)

Q30.The following pairs of compounds can be distinguished by simple test−tube reactions.

For each pair of compounds, give a reagent (or combination of reagents) that, when added separately to each compound, could be used to distinguish between them. State what is observed in each case.

(a) Butan−2−ol and 2−methylpropan−2−ol

Reagent .........................................................................................................

Observation with butan−2−ol

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Observation with 2−methylpropan−2−ol

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(b) Propane and propene

Reagent .........................................................................................................

Observation with propane

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Observation with propene

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(c) Aqueous silver nitrate and aqueous sodium nitrate

Reagent .........................................................................................................

Observation with aqueous silver nitrate

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Observation with aqueous sodium nitrate

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(d) Aqueous magnesium chloride and aqueous barium chloride

Reagent .........................................................................................................

Observation with aqueous magnesium chloride

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Observation with aqueous barium chloride

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(Total 12 marks)


Q31.Which statement about ethanal is correct?

A It reacts with Tollens’ reagent to form silver.

B It has a higher boiling point than ethanol.

C Its empirical and molecular formulas are different.

D It belongs to a homologous series with general formula CnH2n+1O

(Total 1 mark)

Q32.Compound J, known as leaf alcohol, has the structural formula CH3CH2CH=CHCH2CH2OH and is produced in small quantities by many green plants. The E isomer of J is responsible for the smell of freshly cut grass.

(a) Give the structure of the E isomer of J.

(1)

(b) Give the skeletal formula of the organic product formed when J is dehydrated using concentrated sulfuric acid.

(1)

(c) Another structural isomer of J is shown below.


Explain how the Cahn-Ingold-Prelog (CIP) priority rules can be used to deduce the full IUPAC name of this compound.

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(d) The effect of gentle heat on maleic acid is shown below.

A student predicted that the yield of this reaction would be greater than 80%.

In an experiment,10.0 g of maleic acid were heated and 6.53 g of organic product were obtained.

Is the student correct? Justify your answer with a calculation using these data.

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(Total 10 marks)

Q33.Glucose can decompose in the presence of microorganisms to form a range of products. One of these is a carboxylic acid (Mr = 88.0) containing 40.9% carbon and 4.5% hydrogen by mass.

(a) Deduce the empirical and molecular formulas of the carboxylic acid formed.

Empirical formula = ...................... Molecular formula = ...................... (4)

(b) Ethanol is formed by the fermentation of glucose. A student carried out this fermentation reaction in a beaker using an aqueous solution of glucose at a temperature of 25 °C in the presence of yeast.

Write an equation for the reaction occurring during fermentation.

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(c) In industry, this fermentation reaction is carried out at 35 °C rather than 25 °C.

Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature.

Advantage ......................................................................................................

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Disadvantage .................................................................................................

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(d) The method used by the student in part (b) would result in the ethanol being contaminated by ethanoic acid.

How does this contamination occur?


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(e) Give two differences between the infrared spectrum of a carboxylic acid and that of an alcohol other than in their fingerprint regions. Use Table A on the Data Sheet.

Difference 1 ...................................................................................................

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Difference 2 ...................................................................................................

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(Total 10 marks)

Q34.Propene can be made by the dehydration of propan-2-ol.

What is the percentage yield when 30 g of propene (Mr = 42.0) are formed from 50 g of propan-2-ol (Mr = 60.0)?

A 60%

B 67%

C 81%

D 86%

(Total 1 mark)

Q35.Alcohols can be prepared from alkenes in various ways.

(a) On a laboratory scale, a mixture of propan-1-ol and propan-2-ol can be prepared from propene in two steps.

In step 1, propene reacts with cold, concentrated sulfuric acid to form intermediate compounds.

In step 2, the intermediate compounds react with water to form the mixture of alcohols.


Name and outline the mechanism for the reaction between propene and concentrated sulfuric acid to form the intermediate compound which gives propan-2-ol in step 2.

Explain why propan-2-ol is the major product of this preparation.

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(b) On an industrial scale ethanol can be produced from ethene by direct hydration or from glucose by fermentation.

State the conditions for the direct hydration reaction.

State two advantages and two disadvantages of the fermentation method compared with the direct hydration method.

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(Total 13 marks)

Q36.Compounds A, B, C and D are isomers with the molecular formula C4H10O They all have a broad absorption in their infrared spectra in the range 3230–3550 cm–1.

(a) Use Table A on the data sheet to identify the bond and the functional group present responsible for this absorption.

............................................................................................................................. (1)

(b) Compounds A and B are both straight-chain compounds. A can be oxidised to form P. B can be oxidised to form Q. P and Q are isomers with molecular formula C4H8O

Tollens’ reagent and Fehling’s solution can be used to distinguish between isomers P and Q. The results shown in the table are obtained.

Compound

Observation with Tollens’ reagent

Observation with Fehling’s solution

P No visible change No visible change

Q Silver mirror formed Brick-red precipitate formed

Use the information about compounds P and Q to identify compounds A and B. Explain your answer with reference to the functional groups in P and Q.

Identity of A .........................................................................................................

Identity of B .........................................................................................................

Explanation .........................................................................................................

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(c) Isomer C is resistant to oxidation. Isomer C reacts to form compound R that has an absorption in its infrared spectrum in the range 1620–1680 cm–1.

State the bond that causes the absorption in the range 1620–1680 –1.

Give the displayed formula of isomer C.

Identify the reagent and give one reaction condition needed to convert C into R.

Bond ....................................................................................................................

Displayed formula of C

Reagent ...............................................................................................................

Condition ............................................................................................................. (4)

(d) Compound D is a branched-chain isomer that can be oxidised to form compounds S and T.

(i) Compound S is obtained by distilling it off as it forms during the oxidation. Compound T is formed when the oxidation takes place under reflux.

Identify the functional groups in S and T.

Explain, with reference to intermolecular forces, why it is possible to obtain compound S but not T from the reaction mixture by distilling off S as soon as it forms.

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(ii) A student claims to have oxidised compound D. The infrared spectrum of the product obtained by the student is shown.


Suggest two ways in which the spectrum shows that compound D has not been oxidised.

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(Total 13 marks)


M1.(a) Any correct skeletal formula (both OH groups must be shown)

1

(b) M1 Displayed formula of correct product Incorrect organic product CE=0 Must be displayed formula but can be shown separately or in the equation

1

M2 Balanced equation

Allow any correct structural formula (or molecular formula C3H4O3) for product in balanced equation Allow any correct formula of propane-1,2-diol (including its molecular formula C3H8O2)

1

(c) M1 flask with condenser vertically above it (without gaps between flask and condenser)

Distillation diagram CE = 0 Condenser must have outer tube for water that is sealed at top and bottom; condenser must have two openings for water in/out (that are open, although these openings do not need to be labelled) Penalise M1 if apparatus is sealed (a continuous line across the top and/or bottom of the condenser is penalised)

1

M2 flask and condenser labelled Allow condensing tube for condenser label


1

(d) Form small(er) bubbles or prevent large bubbles 1

(e) Any one of these four structures:

Allow any correct structural / displayed / skeletal formula For reference:

Carbon 1 Carbon 2 aldehyde alcohol carboxylic acid alcohol aldehyde ketone alcohol ketone

1

[7]

M2. (a) Three conditions in any order for M1 to M3

M1 yeast or zymase

M2 30 °C ≥ T ≤ 42 °C

M3 anaerobic/no oxygen/no air OR neutral pH

M4 C6H12O6 2C2H5OH + 2CO2

OR 2C6H12O6 4C2H5OH + 4CO2

Mark independently Penalise “bacteria” and “phosphoric acid” using the list principle Ignore reference to “aqueous” or “water” (i.e. not part of the list principle) Or other multiples

4


(b) M1 Carbon-neutral Ignore “biofuel”

1

M2 6 (mol/molecules) CO2/carbon dioxide taken in/used/used up (to form glucose or in photosynthesis)

1

M3 6 (mol/molecules) CO2/carbon dioxide given out due to 2 (mol/molecules) CO2/carbon dioxide from fermentation/ Process 2 and 4 (mol/molecules) CO2/carbon dioxide from combustion/Process 3

It is NOT sufficient in M2 and M3 for equations alone without commentary or annotation or calculation

1

(c) M1 (could be scored by a correct mathematical expression)

(Sum of) bonds broken – (Sum of) bonds made/formed = ΔH

OR

(Σ) Breactants – (Σ) Bproducts = ΔH

(where B = bond enthalpy/bond energy) For M1 there must be a correct mathematical expression using ΔH or “enthalpy change”

M2 Reactants = (+) 4719 OR Products = (–) 5750

M3 Overall + 4719 – 5750 = –1031 (kJ mol–1) (This is worth 3 marks) Award full marks for correct answer. Ignore units. M2 is for either value underlined M3 is NOT consequential on M2

3

Award 1 mark ONLY for +1031

Candidates may use a cycle and gain full marks.

M4 Mean bond enthalpies are not specific for this reaction OR they are average values from many different compounds/molecules

Do not forget to award this mark 1


(d) M1 q = m c ΔT (this mark for correct mathematical formula)

M2 = 6688 (J) OR 6.688 (kJ) OR 6.69 (kJ) OR 6.7 (kJ)

M3 0.46g is 0.01 mol therefore ΔH = – 669 kJ mol–1 OR – 670 kJmol–1

OR –668.8 kJ mol–1

Award M1, M2 and M3 for correct answer to the calculation Penalise M3 ONLY if correct answer but sign is incorrect In M1, do not penalise incorrect cases in the formula If m = 0.46 or m = 200.46 OR if ΔT = 281, CE and penalise M2 and M3 If c = 4.81 (leads to 7696) penalise M2 ONLY and mark on for M3 = –769.6 OR –770 Ignore incorrect units in M2

M4 Incomplete combustion Do not forget to award this mark. Mark independently

4 [15]

M3. (a) (i) M1 pentan-3-one only 1

M2 CH3CH2CH2COCH3

(insist on C=O being drawn out) (penalise use of C3H7)

1

(ii) aldehyde (CH3)2CHCH2CHO 1

ketone (CH3)2CHCOCH3

1

(insist on a clear structure for the C=O of the functional groups, but do not be too harsh on the vertical bonds between carbon atom son this occasion) (If both structures correct, but wrong way around, award one mark) (ignore names)

(b) (i) CH3CH2CH2CH2CHO + [O] → CH3CH2CH2CH2COOH (accept C4H9CHO going to C4H9COOH)


(insist on a balanced equation – for example do not credit [O] over the arrow alone)

1

(ii) pentanoic acid (credit pentan–1–oic acid)

1

(c) (i) CH3CH2CH2CH2CH2OH OR pentan–1–ol (If both a structure and a formula are given, credit either correct one of these provided the other is a good, if imperfect, attempt)

1

(ii) Primary (credit 1o or 1)

1 [8]

M4. (a) Allow 1 mark each for any correctly drawn primary, secondary and tertiary alcohol of molecular formula C4H8O

3

Tertiary alcohol cannot be oxidised 1

(b) Region 1500–400 cm–1

1

exact match to spectrum of known compound 1

(c) A B CH3CH2CH2OH CH3CH2–O–CH3 (1) or CH3CH(OH)CH3 (1)

C D one alkene e.g. one cycloalkane e.g.


CH2=CHCH2CH2CH3

CH3–CH=CH–CH2CH3

(CH3)2C=CHCH3

H2C=C(CH3)CH2CH3

(1) etc

E F CH3CH2CHO (1) CH3COCH3 (1)

6 [12]

M5.(a) Eliminate / reduce fire risk; Allow ethanol flammable / burns / combusts.

1

(b) Orange to green; Need full colour change to score mark.

1 [2]

M6. (a) M1 Concentrations of reactants and products remain constant For M1 NOT “equal concentrations” NOT “amount”

1

M2 Forward rate = Reverse / backward rate Credit the use of [ ] for concentration Ignore dynamic, ignore closed system

1

(b) M1 The (forward) reaction / to the right is exothermic or


releases heat OR converse for reverse reaction. 1

M2 The equilibrium responds by absorbing heat / lowering temperature OR Promotes the endothermic reaction by absorbing heat / lowering temperature OR Temperature increase is opposed (by shift to the left) OR Change is opposed by absorbing heat / lowering temperature.

1

(c) (i) A substance that speeds up / alters the rate but is unchanged at the end / not used up.

Both ideas needed Ignore references to activation energy and alternative route.

1

(ii) None OR no change OR no effect OR nothing OR Does not affect it / the position (of equilibrium) OR (The position is) the same or unchanged.

1

(d) (i) An activity which has no net / overall (annual) carbon emissions to the atmosphere OR An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere. OR There is no change in the total amount of carbon dioxide / carbon /greenhouse gas present in the atmosphere.

The idea that the carbon / CO2 given out equals the carbon / CO2 that was taken in Ignore carbon monoxide

1

(ii) A method which shows (see below) OR states in words that two times the first equation + the second equation gives the correct ratio.

2 (CH4 + H2O → CO + 3H2) CH4 + CO2 → 2CO + 2H2

3CH4 + 2H2O + CO2 → 4CO + 8H2

Ratio = 1 : 2 1

[8]


M7. (a) Functional group (isomerism) 1

(b)

M1 Tollens’ (reagent) (Credit ammoniacal silver nitrate OR a description of making Tollens’) (Ignore either AgNO3 or [Ag(NH3)2+] or “the silver mirror test” on their own, but mark M2 and M3)

M2 silver mirror

OR black solid/precipitate (NOT silver precipitate)

M3 (stays) colourless or no change or no reaction

M1 Fehling’s (solution) or Benedict’s solution (Ignore Cu2+(aq) or CuSO4 on their own, but mark on to M2 and M3)

M2 Red solid/precipitate (Credit orange or brown solid)

M3 (stays) blue or no change or no reaction

Mark on from an incomplete/incorrect attempt at the correct reagent, penalising M1

No reagent, CE=0 Allow the following alternatives M1 (acidified) potassium dichromate(VI) (solution) M2 (turns) green M3 (stays) orange/no change OR M1 (acidified) potassium manganate(VII) (solution) M2 (turns) colourless M3 (stays) purple/no change For M3 Ignore “nothing (happens)” Ignore “no observation”

3

(c) (Both have) C=O OR a carbonyl (group) 1

(d) (i) (Free-) radical substitution ONLY Penalise “(free) radical mechanism”

1


(ii) Initiation Cl2 → 2Cl•

Penalise absence of dot once only.

First propagation Cl• + CH3CH2CH3 → •CH2CH2CH3 + HCl OR C3H8

Penalise incorrect position of dot on propyl radical once only. Penalise C3H7• once only

Second propagation Cl2 + •CH2CH2CH3 → CH3CH2CH2Cl + Cl•

OR

C3H7Cl Accept CH3CH2CH2• with the radical dot above/below/to the side of the last carbon.

Termination (must make C6H14) 2 •CH2CH2CH3 → C6H14 or CH3CH2CH2CH2CH2CH3

Use of the secondary free radical might gain 3 of the four marks

4

(e) Mr = 44.06352 (for propane) Mr = 43.98982 (for carbon dioxide)

Mark independently

M1 a correct value for both of these Mr values.

M2 a statement or idea that two peaks appear (in the mass spectrum)

OR

two molecular ions are seen (in the mass spectrum). 2

[12]

M8. (a) M1 Displayed formula for butan-2-ol


M1 displayed formula must have all bonds drawn out, including the O―H but ignore angles Penalise “sticks”

M2 Alcohol X is

M2 structure must be clearly identifiable as 2-methylpropan-2-ol and may be drawn in a variety of ways.

M3 Alcohol Y is named (2)-methylpropan-1-ol ONLY M3 must be correct name, but ignore structures

3

(b) M1 The infrared spectrum shows an absorption/peak in the range 3230 to 3550 (cm–1)(which supports the idea that an alcohol is present)

In M1, allow the words “dip”, “spike”, “low transmittance” and “trough” as alternatives for absorption.

M2 Reference to the ‘fingerprint region’ or below 1500 (cm–1)

M3 Match with or same as known sample/database spectra Check the spectrum to see if alcohol OH is labelled and credit.

OR

M2 Run infrared spectra (of the alcohols)

M3 Find which one matches or is the same as this spectrum. 3

(c) M1 balanced equation C6H12O6 → CH3CH2CH2CH2OH + 2CO2 + H2O or C4H9OH

Or multiples for M1 and M3 In M1 and M3 penalise use of C4H10O or butan-2-ol once only

M2 Any one from

• excess/adequate/sufficient/correct amount of/enough/plenty/ a good supply of oxygen or air


• good mixing of the fuel and air/oxygen For M2, do not accept simply “oxygen” or “air” alone Ignore reference to “temperature”

M3 CH3CH2CH2CH2OH + 6O2 → 4CO2 + 5H2O or C4H9OH

M4 A biofuel is a fuel produced from (renewable) biological (re)source(s)

OR

(renewable) (re)source(s) from (a specified) plant(s)/fruit(s)/tree(s) In M4 Ignore references to “carbon neutral” Ignore “sugar” and “glucose”

4

(d) M1 butan-1-ol is a primary or 1° (alcohol)

M2 Displayed formula (ONLY) for butanal CH3CH2CH2CHO

M3 Displayed formula (ONLY) for butanoic acid CH3CH2CH2COOH M2 and M3 displayed formula must have all bonds drawn out including the O―H but ignore angles. If butanal and butanoic acid formulae are both correctly given but not displayed, credit one mark out of two.

M4 Oxidation (oxidised) OR Redox

M5 orange to green Both colours required for M5 Ignore states

5 [15]

M9.Add Tollens / Fehling’s / Benedict’s reagent / ir spectra Accept any other chemically correct reagent and observation

1

Silver mirror / blue to red OR red precipitate (with ethanal) / peak at 1700 cm–1 (in ethanal)

Must have correct test to access second mark Accept ‘silver’. Do not accept ‘silver solution’


Give one mark for ‘silver mirror test’ and ‘silver mirror’ Accept correct answer based on n.m.r. spectra

1 [2]

M10.Figure 2 1

Further oxidation will occur / ethanoic acid formed Do not accept ‘poor yield’ without qualification Can gain this mark if logic correct but has chosen wrong Figure

1 [2]

M11.(Mix the alcohol with warm) K2Cr2O7 / H+ allows 3° identification by lack of reaction Scheme must allow the alcohol to be distinguished to get all marks.

1

Distillation of initial product needed for 1° / 2° If distillation stage not clear then max. 2 (M1 and M3). Awareness of correct reactions / lack of reaction relating to each class of alcohol is worth 1 mark.

1

Effect of Tollens’ / Fehling’s on oxidation product to identify 1° or 2° (by default) Reacting Tollens’ / Fehling’s with alcohols directly is incorrect and gains no M2 or M3. Detailed observations relating to the reactions are not needed but should be penalised where incorrect.

1 [3]

M12. (a) (i) Hexan-1-ol1 ONLY


1

(ii) Homologous (series) ONLY

1

(iii) Displayed formula for butan-2-ol

All bonds must be drawn out including the O–H bond Ignore bond angles

1

(iv) CH3CH2CH2CH2OH + [O] CH3CH2CH2CHO + H2O Require this whole equation as written or formulae drawn out Penalise “sticks”

1

(v) Displayed formula for butanone

(credit possible enols, ethers and cyclic structures for C4H8O)

All bonds must be drawn out Ignore bond angles

1

(b) M1 q = m c ΔT OR calculation 175 × 4.18 × 8

M2 = 5852 (J) OR 5.85 (kJ) OR 5.9 (kJ) (This also scores M1)

M3 0.005 mol, therefore ΔH = –1170 (kJ mol–1)


OR ΔH = –1170.4 (kJ mol–1)

OR ΔH = –1200 (kJ mol–1) Award full marks for correct answer In M1, do not penalise incorrect cases in the formula Ignore incorrect units in M2 Penalise M3 ONLY if correct answer but sign is incorrect OR value is in J mol–1

If m = 5 × 10–3 OR if ΔT = 281, CE and only allow one mark for correct mathematical formula for M1 If c = 4.81 (leads to 6734) penalise M2 ONLY and mark on for M3 = –1350 (–1347)

3

(c) (i) M1 The enthalpy change (or heat change at constant pressure) when 1 mol of a compound/substance/alcohol

M2 is burned completely in oxygen

OR burned in excess oxygen

M3 with all reactants and products/all substances in standard states

OR

all reactants and products/all substances in normal states under standard conditions OR 100 kPa/1 bar and a specified T/298 K

For M3 Ignore reference to 1 atmosphere

3

(ii) M1 (could be scored by a correct mathematical expression)

M1 ΔH = ΣΔHf (products) – .ΣΔHf (reactants)

OR a correct cycle of balanced equations

M2 = 4(–394) + 5(–286) – (–327)

(This also scores M1)

M3 = – 2679 (kJ mol–1) OR –2680 (kJ mol–1)

Award 1 mark ONLY for (+) 2679 OR (+) 2680 Correct answer to calculation gains full credit Credit 1 mark if + 2679 (kJ mol–1) For other incorrect or incomplete answers, proceed as follows


• check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for correct method; this requires either a correct cycle with 4CO2 and 5H2O OR a clear statement of M1 which could be in words and scores only M1

3

(d) (i) M1 This is about the change in formula up the series

Each alcohol in the series (compared with the previous one)

increases by/has an extra CH2

OR

has one more C-C and two more C-H

M2 This is about the reaction and bond breaking/making

Combustion of each alcohol in the series breaks one

more C-C and two more C-H compared with the previous one AND forms one more mol CO2 and one more mol H2O

OR

A statement in which there is the idea that the extra OR additional OR difference in number of bonds broken and formed (as the series increases) is the same OR has the same difference in energy N.B. If the first statement here for M2 is given, both marks score

2

(ii) For the two marks M1 and M2

heat loss or heat absorbed by the apparatus

OR

incomplete combustion/not completely burned

OR

The idea that the water may end up in the gaseous state (rather than liquid) OR reactants and/or products may not be in standard states.


2 [18]

M13. (a) to neutralise stomach acidity

OR

as an antacid

OR

eases indigestion/heartburn Ignore milk of magnesia Credit suitable reference to indigestion/laxative/relief of constipation

1

(b) (i) an electron acceptor

OR

(readily) gains/accepts/receives electron(s) NOT an electron pair acceptor Ignore removes/takes away/attracts electrons

1

(ii) Br2 ONLY Ignore “bromine” Apply the list principle

1

(iii) H2SO4 + 2H+ + 2e– SO2 + 2H2O

OR

SO42– + 4H+ + 2e– SO2 + 2H2O Ignore state symbols Ignore absence of negative charge on electron Or multiples of equations

1


(c) (i) (acid) catalyst

OR

catalyses (the reaction)

OR

to speed up the reaction/increase the rate (of reaction) Ignore “provides H+ ions” Accept phonetic spelling

1

(ii)

M1 must show an arrow from the double bond towards the H atom of the H – O bond OR HO on a compound with molecular formula for H2SO4 (or accept H2SO3 here) M1 could be to an H+ ion and M2 an independent O – H bond break on a compound with molecular formula for H2SO4 or H2SO3

M2 must show the breaking of the O ─ H bond.

M3 must show an arrow from the lone pair of electrons on the correct oxygen of the negatively charged ion towards the positively charged carbon atom.

M4 is for the structure of the carbocation.

NB The arrows here are double-headed M2 Ignore partial charges unless wrong M3 NOT HSO4–


For M3, credit as shown or ―:OSO3H ONLY with the negative charge anywhere on this ion OR correctly drawn out with the negative charge placed correctly on oxygen Max 3 marks for wrong reactant Do not penalise the use of “sticks”

4

(iii) Primary OR 1° (alcohol) 1

(iv) Displayed formula for ethanoic acid, CH3COOH

All the bonds must be drawn out and this includes the O ─ H bond Ignore bond angles.

1 [11]

M14. (a) M1 AgNO3 OR silver nitrate OR any soluble silver salt

M2 remains colourless or no reaction or no (observed) change or no precipitate

M3 white precipitate or white solid/white suspension An insoluble silver salt OR Tollens’ OR ammoniacal silver nitrate or HCl/AgNO3 is CE = 0 for the clip For M1 Credit acidified (or HNO3) silver nitrate for M1 and mark on If silver ions or incorrect formula for silver nitrate, penalise M1 but mark M2 and M3 If no reagent or incorrect reagent in M1, then no marks for M2 or M3 For M2 Ignore “nothing” Ignore “no observation” Ignore “clear”


Ignore “dissolves” For M3 Ignore “cloudy solution” OR “suspension”

3

(b) M1 any soluble sulfate by name or formula e.g. sodium sulfate or sulfuric acid.

M2 white precipitate or white solid/white suspension

M3 remains colourless or no reaction or no (observed) change or no precipitate

OR as an alternative

M1 NaOH/KOH

M2 remains colourless or no reaction or no (observed) change

M3 white precipitate or white solid/white suspension An insoluble sulfate OR conc H2SO4 is CE = 0 for the clip If no reagent or incorrect reagent in M1, then no marks for M2 or M3 For the M1 soluble sulfate If sulfate ions or incorrect formula for the chosen sulfate, penalise M1 but mark M2 and M3 For the M1 NaOH/KOH If ammonia, then CE = 0 If hydroxide ions or incorrect formula for the chosen hydroxide, penalise M1 but mark M2 and M3 For no (observed) change in both alternatives Ignore “nothing” Ignore “no observation” Ignore “clear” Ignore “dissolves” For the white precipitate in both alternatives Ignore “cloudy solution” OR “suspension”

3

(c) M1 ammonia (can be dilute or concentrated)

M2 dissolves OR soluble OR (forms a) colourless solution OR goes colourless

M3 does not dissolve OR not soluble OR remains as a solid


OR no (observed) change OR no reaction OR yellow solid remains

OR if concentrated ammonia has been used, accept yellow solid turns white.

OR as an alternative using conc sulfuric acid

M1 concentrated sulfuric acid OR c(onc) H2SO4

M2 misty/white fumes/gas

OR remains white

OR no change (in colour)

M3 turns black (solid)

OR purple fumes/gas

OR correct reference to H2S observation (e.g. bad egg smell) For M1 If incorrect formula or “ammonium”, penalise M1 but mark M2 and M3 If no reagent or incorrect reagent in M1, then no marks for M2 or M3 For M3 Ignore “nothing” Ignore “no observation” For the alternative using sulfuric acid If dilute sulfuric acid or “aq” (alone) or the idea of concentrated not included CE = 0 If incorrect formula, penalise M1 but mark M2 and M3 If no reagent or incorrect reagent in M1, then no marks for M2 or M3

3

(d) M1 acidified potassium dichromate or K2Cr2O7/H2SO4

OR K2Cr2O7/H+ OR acidified K2Cr2O7

M2 (orange to) green solution OR goes green

M3 (solution) remains orange or no reaction or no (observed) change

Alternative using KMnO4/H2SO4


M1 acidified potassium manganate(VII) or KMnO4/H2SO4

OR KMnO4/H+ OR acidified KMnO4

M2 colourless solution OR goes colourless

M3 (solution) remains purple or no reaction or no (observed) change If no reagent or incorrect reagent in M1, then no marks for M2 or M3 For M1 If “dichromate” or “dichromate(IV)” or incorrect formula or no acid, penalise M1 but mark M2 and M3 For M2 ignore dichromate described as “yellow” or “red” For M3 Ignore “nothing” Ignore “no observation” For M1 If “manganate” or “manganate(IV)” or incorrect formula or no acid, penalise M1 but mark M2 and M3 Credit alkaline KMnO4 for possible full marks but M2 gives brown precipitate or solution goes green

3 [12]

M15.(a) M1 C6H12O6 2CH3CH2OH + 2CO2

(2C2H5OH) Mark independently For M1 and M3 ignore state symbols and credit multiples For M1 and M3 penalise C2H6O once only

M2 fermentation

M3 CH3CH2OH + 3O2 2CO2 + 3H2O (C2H5OH)

M4 A specified process e.g. planting / harvesting / transport / extracting sugar / distilling ethanol solution / fertiliser production etc.

M5 The specified process uses / burns (fossil) fuel that releases CO2

For M5, “releases / increases carbon emissions” is insufficient as an alternative to releases CO2

5


(b) M1 sodium or potassium hydroxide / NaOH / KOH Mark on to M2 from hydroxide ion

M2 depends on correct M1 Ignore OH– if KOH/ OH–

warm / heat / reflux and aqueous or (aq) or water For M2 ignore “dilute” For M2 penalise T > 100 °C

M3 nucleophilic substitution Acidified KOH/NaOH or H2SO4 with KOH/NaOH loses M1 and M2

For M3, both words required

NB The arrows here are double-headed

M4 must show an arrow from the lone pair of electrons on the oxygen atom of the negatively charged hydroxide ion to the C atom.

Penalise M4 if covalent NaOH / KOH is used Penalise one mark from M4 or M5 if half-headed arrows are used

M5 must show the movement of a pair of electrons from the

C— Br bond to the Br atom. Mark M5 independently provided it is from their original molecule.

Penalise M5 for formal charge on C of the C–Br or incorrect partial charges on C–Br Penalise once only for a line and two dots to show a bond.

For M4 and M5, award full marks for an SN1 mechanism For M4 and M5, maximum 1 of 2 marks if wrong reactant is used. Penalise M5 if an extra arrow is drawn from the Br of the C–Br bond to, for example, K+span> Do not penalise the use of “sticks”

M6 One statement from

• The yield is (very) low / not a high yield OR elimination occurs / ethene formed

• The rate of reaction slow


• Bromoethane has to be manufactured / made first

• Bromoethane is expensive For M6 ignore references to other costs and expenses

6

(c) M1 concentrated phosphoric acid / conc. H3PO4 OR concentrated sulfuric acid /conc. H2SO4

Answers in any order Ignore reference to support medium in M1

M2 hydration or (electrophilic) addition

For M3 and M4 any two from Do not apply the list principle to these three chosen criteria in M3 and M4

• Excess ethene

OR Excess steam / water / H2O

OR remove the ethanol as it forms

OR recycle the ethene

• Specified Pressure

50 atm ≤ P ≤ 100 atm

OR 5000 kPa ≤ P ≤ 10000 kPa

OR 5 MPa ≤ P ≤ 10 MPa

• HighTemperature unless they give a value that is not in the ranges given here;

OR 300 °C ≤ T ≤ 600 °C

OR 570 K ≤ T ≤ 870 K Accept a reference to “low temperature” if they specify a correct temperature range or a correct temperature in the range

4 [15]

M16.(a) (i) Green Ignore shades of green.

1


(ii) Excess acidified potassium dichromate(VI) 1

Reflux (for some time) 1

In the diagram credit should be given for • a vertical condenser

Lose M3 and M4 for a distillation apparatus. 1

• an apparatus which would clearly work Do not allow this mark for a flask drawn on its own. Penalise diagrams where the apparatus is sealed.

1

(iii) Distillation 1

Immediately (the reagents are mixed) 1

(b) Keep away from naked flames Allow heat with water-bath or heating mantle. If a list is given ignore eye protection, otherwise lose this mark.

1

(c) (i) Tollens’ or Fehling’s reagents Incorrect reagent(s) loses both marks. Accept mis-spellings if meaning is clear.

1

Silver mirror / red ppt. formed Accept ‘blue to red’ but not ‘red’ alone.


1

(ii) Sodium carbonate (solution) / Group II metal Allow indicator solutions with appropriate colours. Accept any named carbonate or hydrogen carbonate.

1

Effervescence / evolves a gas Accept ‘fizzes’.

1

(d) Propanoic acid If this mark is lost allow one mark if there is reference to stronger intermolecular forces in the named compound. Lose M1 and M3.

1

Contains hydrogen bonding 1

Some comparison with other compounds explaining that the intermolecular forces are stronger in propanoic acid

1 [15]

M17. (a) Pentan-2-one ONLY but ignore absence of hyphens

1

(b) Functional group (isomerism) Both words needed

1

(c) (i)


Award credit provided it is obvious that the candidate is drawing the Z / cis isomer The group needs to be CHOHCH3 but do not penalise poor C–C bonds or absence of brackets around OH Trigonal planar structure not essential

1

(ii) Restricted rotation (about the C=C)

OR

No (free) rotation (about the C=C) 1

(d)

M1 Tollens’ (reagent)

(Credit ammoniacal silver nitrate OR a description of making Tollens’)

(Do not credit Ag+, AgNO3 or [Ag(NH3)2+] or “the silver mirror test”

on their own, but mark M2 and M3)

M1 Fehling’s (solution) / Benedict’s

(Penalise Cu2+(aq) or CuSO4 but mark M2 and M3)

M2 silver mirror

OR black solid or black precipitate

M2 Red solid/precipitate

(Credit orange or brown solid)

M3 (stays) colourless

OR

no (observed) change / no reaction

M3 (stays) blue

OR

no (observed) change / no reaction

If M1 is blank CE = 0, for the clip Check the partial reagents listed and if M1 has a totally incorrect reagent, CE = 0 for the clip Allow the following alternatives M1 (acidified) potassium dichromate(VI) (solution); mark on from incomplete formulae or incorrect oxidation state M2 (turns) green M3 (stays) orange / no (observed) change / no reaction OR M1 (acidified) potassium manganate(VII) (solution); mark on from incomplete formulae or incorrect oxidation state


M2 (turns) colourless M3 (stays) purple / no (observed) change / no reaction In all cases for M3 Ignore “nothing (happens)” Ignore “no observation”

3

(e) (i) Spectrum is for Isomer 1

or named or correctly identified The explanation marks in (e)(ii) depend on correctly identifying Isomer 1. The identification should be unambiguous but candidates should not be penalised for an imperfect or incomplete name. They may say “the alcohol” or the “alkene” or the “E isomer”

1

(ii) If Isomer 1 is correctly identified, award any two from

• (Strong / broad) absorption / peak in the range 3230 to 3550 cm–1 or specified value in this range or marked correctly on spectrum and (characteristic absorption / peak for) OH group /alcohol group

• No absorption / peak in range 1680 to 1750 cm–1 or absence marked correctly on spectrum and (No absorption / peak for a) C=O group / carbonyl group / carbon-oxygen double bond

• Absorption / peak in the range 1620 to 1680 cm–1

or specified value in this range or marked correctly on spectrum and

(characteristic absorption / peak for) C=C group / alkene / carbon-carbon double bond If 6(e)(i) is incorrect or blank, CE=0 Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption. Ignore reference to other absorptions e.g. C-H, C-O

2 [10]


M18.(a) HOOC—CHOH—CHOH—COOH Any suitable structural formula. Displayed formula not required but bond sequences must be correct if shown.

1

(b) C4H6O6 + NaHCO3 → C4H5O6Na + CO2 + H2O

OR

C4H6O6 + 2NaHCO3 → C4H4O6Na2 + 2CO2 + 2H2O Allow equations based on the structural formula. Allow multiples including fractions. Allow any structure for C4H6O or C4H5O6Na

1

(c) Suitable named indicator (eg litmus, methyl orange, Universal Indicator) / identified reactive metal (Mg, Zn or Fe)

Do not allow phenolphthalein without explanation of how a colour change would be seen. Incorrect reagent, chemical error = 0 / 2

1

Appropriate colour in acid (eg red) / gas evolved 1

(d) (i) Reagent: Acidified potassium dichromate (solution) If incomplete (correct) reagent, lose M1 but mark on. Incorrect reagent, chemical error = 0 / 3 Allow acidified potassium manganate(VII)

1

Obs: orange to green Purple to colourless (solution).

1

Obs: no (visible) change


Allow ‘no visible reaction’, but do not allow ‘no reaction’ without qualification.

1

(ii) Both would give the same result / both oxidised by reagent / both react with the reagent or similar

Allow consequential answer from (i). Chemical error if reagent in (i) is incorrect, 0 / 1

1

(e) The water would allow the tartaric acid and sodium hydrogencarbonate to react (before use)

Ignore any reference to water reacting with the ingredients. Ignore references to prevention of ‘caking’ or ‘clumping’. Ignore references to shelf life without qualification.

1

(f) Acid reacts (with NaHCO3 / Na2CO3) to form CO2

Allow ‘neutralises (NaHCO3 / Na2CO3) to form CO2’. 1

(g) It is only used in very small quantities Allow ‘decomposes in the reaction’. Do not allow ‘reacts’ without qualification. Ignore reference to formation of salts.

1 [11]

M19.(a) To prevent vigorous boiling / uneven boiling / bubbling vigorously Reference to an effect on ‘reaction’ here loses this mark.

1

(b) Condenser Accept ‘condensation chamber’ or ‘condensation tube’.

1

Should show effective water jacket and central tube


If a flask is also drawn then the condenser must be at an appropriate angle. Apparatus must clearly work. Ignore direction of water flow. Diagram must have a clear flow of vapour and water eg unblocked central tube or flow indicated by arrows.

1 [3]

M20. (a) M1 Safety (in Process 1)

Sodium hydroxide / alkali is corrosive / harmful / caustic or sodium hydroxide is alkali(ne)

Ignore references to chromium compounds

OR

Bromine compounds are toxic / poisonous “Carbon-neutral” alone is insufficient for M2

M2 Environmental Ignore references to greenhouse gases

Process 2 could be used as a carbon sink / for carbon capture

OR

uses waste / recycled CO2 / CO2 from the factory / CO2 from the bioethanol (or biofuel) production

OR

reduces or limits the amount of CO2 released / given out (into the atmosphere)

OR

Process 2 uses renewable glucose / renewable resource(s) 2

(b) (i) M1 nucleophilic substitution For M1, both words required

M2 must show an arrow from the lone pair of electrons on the oxygen atom of


the negatively charged hydroxide ion to the C atom. Penalise M2 if covalent NaOH / KOH is used Penalise one mark from M2 or M3 if half-headed arrows are used

M3 must show the movement of a pair of electrons from the C–Br bond to the Br atom. Mark M3 independently provided it is from the original molecule

Penalise M3 for formal charge on C of the C–Br or incorrect partial charges on C–Br Penalise once only for a line and two dots to show a bond.

For M2 and M3 award full marks for an SN1 mechanism For M2 and M3, maximum 1 of 2 marks for the mechanism if wrong reactant is used. Penalise M3 if an extra arrow is drawn from the Br of the C–Br bond to, for example, K+

Accept the correct use of “sticks

NB The arrows here are double-headed 3

(ii) M1 B

M2 C

M3 A 3

(c) M1 fermentation Mark M2 to M4 independently

Three conditions in any order for M2 to M4 Penalise “bacteria” and “phosphoric acid” using the list principle

M2 (enzymes from) yeast or zymase

M3 25°C ≤ T ≤ 42°C OR 298 K ≤ T ≤ 315 K Ignore reference to “aqueous” or “water”, “closed container”, “pressure, “lack of oxygen”, “concentration of ethanol” and “batch process” (i.e. not part of the list principle)

M4 anaerobic / no oxygen / no air OR neutral pH 4

(d) M1 primary OR 1° (alcohol) Mark independently


M2 acidified potassium or sodium dichromate For M2, it must be a whole reagent and/or correct formulae

OR H2SO4 / K2Cr2O7 OR H+ / K2Cr2O7

Do not penalise incorrect attempt at formula if name is correct or vice versa Accept phonetic spelling If oxidation state given in name, it must be correct. For M2 accept acidified potassium manganate(VII)

OR correct combination of formula and name

M3

HOCH2CH2CH2CH2OH + 4[O] HOOCCH2CH2COOH + 2H2O For M3 structures must be correct and not molecular formula

3 [15]

M21.(a) (i) CH2O Atoms in any order Accept a clear indication that C6H12O6 yields CH2O as the answer

1

(ii) No peak / no absorption / no C=O in the range 1680 to 1750 (cm−1) (suggesting no evidence of C=O)

Allow the words “dip”, “spike”, “low transmittance” and “trough” as alternatives for absorption Ignore references to other wavenumbers

1

(b) M1 C6H12O6 2CH3CH2OH + 2CO2

Penalise (C2H6O) Allow multiples of the equation in M1

Either order M2 (enzymes from) yeast or zymase

M3 25 °C ≤ T ≤ 42 °C OR 298 K ≤ T ≤ 315 K For M2 and M3 Ignore “aqueous” Ignore “anaerobic / absence of oxygen”


Ignore “controlled pH” Ignore “warm”

3

(c) (i) Displayed formula for CH3COOH

All bonds must be drawn out, but ignore bond angles

1

(ii) O2 + 4H+ + 4e− 2H2O Ignore state symbols Negative charge on electron not essential Accept multiples Accept electrons subtracted from RHS

1

(iii) CH3CH2OH + H2O CH3COOH + 4H+ + 4e–

(C2H6O or C2H5OH) Ignore state symbols Negative charge on electron not essential Accept multiples Accept electrons subtracted from LHS

1

(iv) M1 Acidified potassium or sodium dichromate For M1, it must be a whole reagent and / or correct formulae

OR H2SO4 / K2Cr2O7 OR H+ / K2Cr2O7 etc. Do not penalise incorrect attempt at formula if name is correct or vice versa

OR correct combination of formula and name If oxidation state given in name, it must be correct, but mark on from an incorrect attempt at a correct reagent.

M2 (requires an attempt at M1) orange to green


Credit acidified potassium chromate(VI) / H2SO4 + K2CrO4

Possible alternative M1 (acidified) potassium manganate(VII) OR KMnO4 / H2SO4

M2 purple to colourless Other alternatives will be accepted but M2 is dependent on M1 in every case M2 requires an attempt at a correct reagent for M1 Ignore reference to states

2

(d) (i) An activity which has no net / overall (annual) carbon emissions to the atmosphere / air

The idea that the carbon / CO2 given out equals the carbon / CO2 that was taken in from the atmosphere / air

OR

An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere / air.

Answer must refer to the atmosphere or air

OR

There is no change in the total amount of carbon dioxide / carbon /greenhouse gas present in the atmosphere / air

1

(ii) Renewable / sustainable ONLY Ignore references to global warming or greenhouse gases

1

(iii) Any one statement about this process from

Subject to weather / climate Ignore “batch”

OR

Depletes food supply OR the land use for (specified) food

OR

Requires use of / uses more fossil fuels

OR

Not carbon-neutral OR CO2 produced during a named process (eg harvest, transport etc.)


OR

Slow process / slow rate of reaction / takes a long time (to grow crops)

OR

This route leads to the production of a mixture of water and ethanol / impure ethanol that requires separation / further processing

1 [13]

M22.(a) (i) 2C6H12O6 3CH3COCH3 + 3CO2 + 3H2O

Or multiples 1

(ii) to speed up the reaction OR (provide a) catalyst or catalyses the reaction or biological catalyst OR release / contain / provides an enzyme

Ignore “fermentation” Ignore “to break down the glucose” Not simply “enzyme” on its own

1

(b) (i) CH3CH(OH)CH3 + [O] CH3COCH3 + H2O Any correct representation for the two organic structures. Brackets not essential. Not “sticks” for the structures in this case

1

(ii) Secondary (alcohol) OR 2° (alcohol) 1

(c) M1 q = m c ΔT

OR q =150 × 4.18 × 8.0 Award full marks for correct answer In M1, do not penalise incorrect cases in the formula

M2 = (±) 5016 (J) OR 5.016 (kJ) OR 5.02 (kJ) (also scores M1)

M3 This mark is for dividing correctly the number of kJ by the number of moles and arriving at a final answer in the range shown.


Using 0.00450 mol

therefore ΔH = − 1115 (kJ mol−1 )

OR − 1114.6 to − 1120 (kJ mol−1 )

Range (+)1114.6 to (+)1120 gains 2 marks

BUT − 1110 gains 3 marks and +1110 gains 2 marks

AND − 1100 gains 3 marks and +1100 gains 2 marks Award full marks for correct answer In M1, do not penalise incorrect cases in the formula Penalise M3 ONLY if correct numerical answer but sign is incorrect; (+)1114.6 to (+)1120 gains 2 marks Penalise M2 for arithmetic error and mark on If ΔT = 281; score q = m c ΔT only If c = 4.81 (leads to 5772) penalise M2 ONLY and mark on for M3 = − 1283 Ignore incorrect units in M2 If units are given in M3 they must be either kJ or kJ mol−1 in this case

3

(d) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / element

M2 is burned / combusts / reacts completely in oxygen OR burned / combusted / reacted in excess oxygen

M3 with (all) reactants and products / (all) substances in standard / specified states

OR (all) reactants and products / (all) substances in normal states under standard conditions / 100 kPa / 1 bar and specified T / 298 K


3

(e) M1 Σ B (reactants) − Σ B (products) = ΔH OR Sum of bonds broken − Sum of bonds formed = ΔH OR 2B(C−C) + B(C=O) + 6B(C−H) + 4B(O=O) (LHS)

− 6B(C=O) − 6B(O−H) (RHS) = ΔH

M2 (also scores M1)


2(348)+805+6(412)+4(496) [LHS = 5957]

(696) (2472) (1984)

− 6(805) − 6(463) [RHS = (−) 7608] = ΔH

(4830) (2778)

OR using only bonds broken and formed (5152 − 6803)

M3 ΔH= − 1651 (kJ mol−1)

Candidates may use a cycle and gain full marks. Correct answer gains full marks Credit 1 mark for (+) 1651 (kJ mol−1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication / addition error; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 4O2, 3CO2 and 3H2O OR a clear statement of M1 which could be in words and scores only M1

Allow a maximum of one mark if the only scoring point is LHS = 5957 (or 5152) OR RHS = 7608 (or 6803) Award 1 mark for + 1651

3

(f) For the two marks M1 and M2, any two from • heat loss or not all heat transferred to the apparatus or heat absorbed by

the apparatus or (specific) heat capacity of the apparatus not considered • incomplete combustion / not completely burned / reaction is not complete • The idea that the water may end up in the gaseous state (rather than

liquid) • reactants and / or products may not be in standard states. • MBE data refers to gaseous species but the enthalpy of combustion refers

to liquids in their standard states / liquid propanone and liquid water in standard states

• MBE do not refer to specific compounds OR MBE values vary with different compounds / molecules OR are average / mean values taken from a range of compounds / molecules

Apply the list principle but ignore incomplete reasons that contain correct chemistry Ignore “evaporation” Ignore “faulty equipment” Ignore “human error” Not enough simply to state that “MBE are mean / average values”

2 [15]


M23.(a) Structure for 3-methylbut-1-ene

H2C=CHCH(CH3)2

Any correct structural representation. Credit “sticks” and require the double bond.

1

(b) Structure for 2-methylpropan-2-ol

(CH3)3COH Any correct structural representation. Credit “sticks”.

1

(c) Structure for propene

H2C=CHCH3


1

(d) Structure for 2-aminobutane

CH3CH2CH(NH2)CH 3

Any correct structural representation. Credit “sticks”.

1 [4]

M24.Acidified potassium dichromate Accept words or formulae. Accept acidified potassium permanganate. Accept Lucas reagent (conc HCl, ZnCl2) (cloudy in 5 mins for 2°, instantly for 3°). Mark on for incomplete reagent. Incorrect reagent CE = 0 / 3 Inclusion of Tollen’s etc with acidified potassium dichromate is incorrect reagent. Not no reaction.


Either

Obs with 2-methylpropan-2-ol

No visible change 1

Obs with butan-2-ol

Orange to green (both colours needed) 1

or

Obs with 2-methylpropan-2-ol

orange

Obs with butan-2-ol green

[3]

M25.Identification of acid by suitable method eg named indicator, named carbonate, specified reactive metal

Ignore any reference to the smell of the ester. 1

with expected results Do not allow the use of any instrumental method eg i.r. or n.m.r.; must be a chemical test.

1

Identification of alcohol by suitable method eg oxidation by acidified potassium dichromate(VI)

1

with expected results 1

[4]


M26.(a) H2SO4

Allow H3PO4 or HCl 1

(b) Dichromate / Cr(VI) reduced or Cr(III) formed. Allow Cr6+ and Cr3+

1

(c) The alcohol is flammable Allow enables temperature to be controlled

1

(d) Tollens’ 1

Silver mirror OR Fehling’s Red precipitate OR Benedict’s Red precipitate

1 [5]

M27.(a)

M1 C6H12O6 2CH3CH2OH (2C2H5OH)

+ 2CO2

Penalise C2H6O for ethanol in M1.

M2 and M3 Mark M2 and M3 independently.

Any two conditions in any order for M2 and M3 from

• (enzymes from) yeast or zymase

• 25 °C ≤ T ≤ 42 °C OR 298 K ≤ T ≤ 315 K

• anaerobic / no oxygen / no air OR neutral pH A lack of oxygen can mean either without oxygen or not having enough oxygen and does not ensure no oxygen, therefore only credit “lack of oxygen” if it is qualified.


Penalise ‘bacteria’, ‘phosphoric acid’, ‘high pressure’ using the list principle.

M4 (fractional) distillation or GLC Ignore reference to ‘aqueous’ or ‘water’ (ie not part of the list principle).

M5 Carbon-neutral in this context means

There is no net / overall (annual) carbon dioxide / CO2 emission to the atmosphere

OR

There is no change in the total amount / level of carbon dioxide / CO2 present in the atmosphere

For M5 – must be about CO2 and the atmosphere. The idea that the carbon dioxide / CO2 given out equals the carbon dioxide / CO2 that was taken in from the atmosphere.

5

(b) M1 q = m c ∆T (this mark for correct mathematical formula) Full marks for M1, M2 and M3 for the correct answer. In M1, do not penalise incorrect cases in the formula.

M2 = (75 × 4.18 × 5.5)

1724 (J) OR 1.724 (kJ) OR 1.72 (kJ) OR 1.7 (kJ)

(also scores M1) Ignore incorrect units in M2.

M3 Using 0.0024 mol

therefore ∆H = − 718 (kJ mol−1)

(Accept a range from −708 to −719 but do not penalise more than 3 significant figures)

Penalise M3 ONLY if correct numerical answer but sign is incorrect. Therefore +718 gains two marks. If units are quoted in M3 they must be correct. If ∆T = 278.5, CE for the calculation and penalise M2 and M3.

M4 and M5 in any order

Any two from

• incomplete combustion

• heat loss

• heat capacity of Cu not included

• some ethanol lost by evaporation


• not all of the (2.40 × 10−3 mol) ethanol is burned / reaction is incomplete If c = 4.81 (leads to 1984) penalise M2 ONLY and mark on for M3 = − 827

5

(c) (i) M1 enthalpy / heat / energy change (at constant pressure) or enthalpy / heat / energy needed in breaking / dissociating (a) covalent bond(s)

Ignore bond making.

M2 averaged for that type of bond over different / a range of molecules / compounds

Ignore reference to moles. 2

(ii) M1

∑ B(reactants) − ∑ B(products) = ∆H

OR

Sum of bonds broken − Sum of bonds formed = ∆H

OR

B(C-C) + B(C-O) + B(O-H) + 5B(C-H) + 3B(O=O) – 4B(C=O) – 6B(O–H) = ∆H = −1279

Correct answer gains full marks. Credit 1 mark for − 496 (kJ mol−1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2). If no AE, check for a correct method; this requires either a correct cycle with 2CO2 and 3H2O OR a clear statement of M1 which could be in words and scores only M1.

M2 (also scores M1) 348+360+463+5(412)+ 3B(O=O)

(3231) (or 2768 if O–H cancelled) − 4(805) − 6(463) = ∆H = − 1279

(5998) (or 5535 if O–H cancelled)

3B(O=O) = 1488 (kJ mol−1) Credit a maximum of one mark if the only scoring point is bonds formed adds up to 5998 (or 5535) OR bonds broken includes the calculated value of 3231 (or 2768).

M3


B(O=O) = 496 (kJ mol−1)

Award 1 mark for −496

Students may use a cycle and gain full marks 3

[15]

M28.(a) 3-methylbutan-2-ol 1

(b)

Allow (CH3)2CHCOCH3

1

(c) Elimination 1

(d)

Allow (CH3)2C=CHCH3

1

Allow (CH3)2CHCH=CH2

1


(e) Position 1

(f) C B A 1

(g)

Allow (CH3)2C(OH)CH2CH3

1

(h)

Allow (CH3)3CCH2OH

1 [9]

M29.(a) A mixture of liquids is heated to boiling point for a prolonged time 1

Vapour is formed which escapes from the liquid mixture, is changed back into liquid and returned to the liquid mixture

1

Any ethanal and ethanol that initially evaporates can then be oxidised 1

(b) CH3CH2OH + H2O CH3COOH + 4H+ + 4e–

1


(c) Mixture heated in a suitable flask / container A labelled sketch illustrating these points scores the marks

1

With still head containing a thermometer 1

Water cooled condenser connected to the still head and suitable cooled collecting vessel

1

Collect sample at the boiling point of ethanal 1

Cooled collection vessel necessary to reduce evaporation of ethanal 1

(d) Hydrogen bonding in ethanol and ethanoic acid or no hydrogen bonding in ethanal

1

Intermolecular forces / dipole-dipole are weaker than hydrogen bonding 1

(e) Reagent to confirm the presence of ethanal:

Add Tollens’ reagent / ammoniacal silver nitrate / aqueous silver nitrate followed by 1 drop of aqueous sodium hydroxide, then enough aqueous ammonia to dissolve the precipitate formed

OR

Add Fehling’s solution 1

Warm M2 and M3 can only be awarded if M1 is given correctly


1

Result with Tollen’s reagent:

Silver mirror / black precipitate

OR

Result with Fehling’s solution:

Red precipitate / orange-red precipitate 1

Reagent to confirm the absence of ethanoic acid

Add sodium hydrogencarbonate or sodium carbonate 1

Result; no effervescence observed; hence no acid present 1

M5 can only be awarded if M4 is given correctly

OR

Reagent; add ethanol and concentrated sulfuric acid and warm

Result; no sweet smell / no oily drops on the surface of the liquid,

hence no acid present [16]

M30.(a) M1 acidified potassium dichromate or K2Cr2O7 / H2SO4

OR K2Cr2O7 / H+ OR acidified K2Cr2O7

M2 (orange to) green solution OR goes green

M3 (solution) remains orange or no reaction or no (observed) change If no reagent or incorrect reagent in M1, CE = 0 and no marks for M1, M2 or M3 If incomplete / inaccurate attempt at reagent e.g. “dichromate” or “dichromate(IV)” or incorrect formula or no acid, penalise M1 only and mark on For M2 ignore dichromate described as “yellow” or “red” For M3 ignore “nothing (happens)” or “no observation”


Alternative using KMnO4 / H2SO4

M1 acidified potassium manganate(VII) / potassium permanganate or KMnO4 / H2SO4

OR KMnO4 / H+ OR acidified KMnO4

M2 colourless solution OR goes colourless

M3 (solution) remains purple or no reaction or no (observed) change For M1 If incomplete / inaccurate attempt at reagent e.g. “manganate” or “manganate(IV)” or incorrect formula or no acid, penalise M1 only and mark on Credit alkaline KMnO4 for possible full marks but M2 gives brown precipitate or solution goes green

3

(b) M1 (Shake with) Br2 OR bromine (water) OR bromine (in CCl4 / organic solvent)

M2 (stays) orange / red / yellow / brown / the same

OR no reaction OR no (observed) change

M3 decolourised / goes colourless / loses its colour / orange to colourless If no reagent or incorrect reagent in M1, CE = 0 and no marks for M1, M2 or M3 If incomplete / inaccurate attempt at reagent (e.g. Br), penalise M1 only and mark on No credit for combustion observations; CE = 0 For M2 in every case Ignore “nothing (happens)” Ignore “no observation” Ignore “clear”

OR as alternatives

Use KMnO4 / H2SO4

M1 acidified potassium manganate(VII) / potassium permanganate OR KMnO4 / H2SO4

OR KMnO4 / H+ OR acidified KMnO4

M2 (stays) purple or no reaction or no (observed) change

M3 decolourised / goes colourless / loses its colour

Use iodine

M1 iodine or I2 / KI or iodine solution


M2 no change

M3 decolourised / goes colourless / loses its colour

Use concentrated sulfuric acid

M1 concentrated H2SO4

M2 no change

M3 brown For M1, it must be a whole reagent and / or correct formula For M1 penalise incorrect attempt at correct formula, but mark M2 and M3 With potassium manganate(VII) If incomplete / inaccurate attempt at reagent e.g. “manganate” or “manganate(IV)” or incorrect formula or no acid, penalise M1 only and mark on Credit alkaline / neutral KMnO4 for possible full marks but M3 gives brown precipitate or solution goes green Apply similar guidance for errors in the formula of iodine or concentrated sulfuric acid reagent as those used for other reagents.

3

(c) M1 Any soluble chloride including hydrochloric acid (ignore concentration)

M2 white precipitate or white solid / white suspension

M3 remains colourless or no reaction or no (observed) change or no precipitate or clear solution or it remains clear


M1 Any soluble iodide including HI

M2 yellow precipitate or yellow solid / yellow suspension



M1 Any soluble bromide including HBr

M2 cream precipitate or cream solid / cream suspension



M1 NaOH or KOH or any soluble carbonate


M2 brown precipitate or brown solid / brown suspension with NaOH / KOH (white precipitate / solid / suspension with carbonate)


If no reagent or incorrect reagent or insoluble chloride in M1, CE = 0 and no marks for M1, M2 or M3 Allow chlorine water If incomplete reagent (e.g. chloride ions) or inaccurate attempt at formula of chosen chloride, or chlorine, penalise M1 only and mark on For M2 require the word “white” and some reference to a solid. Ignore “cloudy solution” OR “suspension” (similarly for the alternatives) For M3 Ignore “nothing (happens)” Ignore “no observation” Ignore “clear” on its own Ignore “dissolves”

3

(d) M1 Any soluble sulfate including (dilute or aqueous) sulfuric acid


M3 white precipitate or white solid / white suspension If no reagent or incorrect reagent or insoluble sulfate in M1, CE = 0 and no marks for M1, M2 or M3 Accept MgSO4 and CaSO4 but not barium, lead or silver sulfates If concentrated sulfuric acid or incomplete reagent (e.g. sulfate ions) or inaccurate attempt at formula of chosen sulfate, penalise M1 only and mark on For M3 (or M2 in the alternative) require the word “white” and some reference to a solid. Ignore “cloudy solution” OR “suspension” For M2 (or M3 in the alternative) Ignore “nothing (happens)” Ignore “no observation” Ignore “clear” on its own Ignore “dissolves”


M1 NaOH or KOH

M2 white precipitate or white solid / white suspension



If incomplete reagent (e.g. hydroxide ions) or inaccurate attempt at formula of chosen hydroxide, penalise M1 only and mark on If M1 uses NH3 (dilute or concentrated) penalise M1 only and mark on

3 [12]

M31.A [1]

M32.(a)

1

(b) 1

(c) Stage 1: consider the groups joined to right hand carbon of the C=C bond Extended response Maximum of 5 marks for answers which do not show a sustained line of reasoning which is coherent, relevant, substantiated and logically structured.

Consider the atomic number of the atoms attached M1 can be scored in stage 1 or stage 2

1

C has a higher atomic number than H, so CH2OH takes priority 1

Stage 2: consider the groups joined to LH carbon of the C=C bond

Both groups contain C atoms, so consider atoms one bond further away 1


C, (H and H) from ethyl group has higher atomic number than H, (H and H) from methyl group, so ethyl takes priority

1

Stage 3: conclusion

The highest priority groups, ethyl and CH2OH are on same side of the C=C bond so the isomer is Z

Allow M5 for correct ECF conclusion using either or both wrong priorities deduced in stages 1 and 2

1

The rest of the IUPAC name is 3-methylpent-2-en-1-ol 1

(d) Moles of maleic acid = 10.0 / 116.0 = 8.62 × 10–2

AND mass of organic product expected = (8.62 × 10–2) × 98.0 = 8.45 g

Or moles of organic product formed = 6.53 / 98.0 = 6.66 × 10–2

1

% yield = 100 × 6.53 / 8.45

OR = 100 × (6.66 × 10–2) / (8.62 × 10–2)

= 77.294 = 77.3%

AND statement that the student was NOT correct 1

[10]

M33.(a) Percentage of oxygen by mass = 100 – 40.9 – 4.5 = 54.6 1

C H O

% Divide by Ar


= 3.41 = 4.5 = 3.41

1

Divide by smallest =

Nearest whole number ratio = 1 × 3 1.32 × 3 1 × 3

= 3 : 3.96 : 3

Nearest integer ratio = 3 : 4 : 3 1

Empirical formula C3H4O3

Empirical formula mass = 88 = molecular formula mass

Therefore, molecular formula is same as the empirical formula - C3H4O3

1

(b) C6H12O6 2C2H5OH + 2CO2

1

(c) Advantage – ethanol is produced at a faster rate 1

Disadvantage – more energy is used / required in the reaction 1

(d) Air gets in / oxidation occurs 1

(e) Alcohol OH absorption in different place (3230–3550 cm–1) from acid OH absorption (2500–3000 cm–1)

1

The C=O in acids has an absorption at 1680–1750 cm–1


1 [10]

M34.D [1]

M35.(a) Electrophilic addition 1

M2 = curly arrow from C=C towards H of H−O on ‘their’ sulfuric acid M3 = curly arrow to break H−O Penalise incorrect dipole/full charges M4 = intermediate M5 = correct anion, lone pair on correct O and curly arrow from that lone pair to C+ on their carbocation IGNORE position of minus sign unless displayed structure IGNORE product

1 1 1 1

Major product/propan-2-ol formed via most stable carbocation/carbonium ion secondary carbocation/carbonium ion more stable (than primary) or reverse argument

M6 for idea of carbocation stability This statement gets M6 and M7 NOT stability of alcohols

1 1

(b) Hot/High T (and High P) ALLOW 200-450 C/473-723 K (Quoted)

1

(SiO2 coated in) phosphoric acid (catalyst)


NOT (aq) 1

advantages of fermentation

• Low(er) T and P / lower energy use

• Less use of non-renewable fossil fuels/renewable/sustainable (resources)

• Low(er) equipment/plant/capital costs IGNORE carbon neutral max 2

1 1

Disadvantages of fermentation

• Slow(er) reaction

• Low atom economy

• Impure product/extra purification/distillation required

• Batch process/labour intensive/difficult to automate

• Land used for sugar crops (so not available for food crops) IGNORE low yield Max 2

1 1

[13]

M36.(a) OH AND alcohol IGNORE hydroxy(l)

1

(b) A = butan-2-ol / CH3CH(OH)CH2CH3

If formulae given then must be unambiguous If both formula and name given then formula must match name for mark to be awarded

1 B = butan-1-ol / CH3CH2CH2CH2OH

1 Product from A / P is a ketone AND Product from B / Q is an aldehyde

Penalise reference to incorrect class of alcohol 1


(c) Type of Bond: C=C 1

Must show all bonds in Isomer C including O–H bond

1 Reagent: conc. H2SO4 / conc. H3PO4

If incorrect attempt at correct reagent, mark on Apply list principle for reagents and conditions marks Conc required - may appear on conditions line NOT (aq) For M3 even if seen on conditions line ALLOW Reagent = Al2O3

Condition = ‘passing vapour over hot solid’ owtte 1

Conditions: 180 °C / High temp / Hot / Reflux / ALLOW stated temp in range 100-300 °C/373-573 K IGNORE ‘heat’ M4 dependent on correct reagent in M3

1

(d) (i) S = aldehyde/CHO AND T = carboxylic/COOH/CO2H 1

T forms hydrogen bonds 1

(Which are) stronger than / need more energy to break than forces between molecules/IMFs in S ora (or reverse argument)

If implication of breaking covalent bonds max M1 only 1

(ii) (No oxidation has occurred as..)

(Still) contains peak at 3230−3550 cm-1 due to O−H/alcohol

Does not contain peak at 2500−3000 cm-1 due to O−H/carboxylic acid

Does not contain peak at 1680−1750 cm-1 due to C=O Must have wavenumber range (or value within range) and bond or functional group to score each mark.

Any 2


[13]

of 69

Alkanes exam pack

Name: ________________________

Class: ________________________

Date: ________________________

Time: 285 minutes

Marks: 266 marks

Comments:

of 69

Q1. When alkanes are burned in an excess of oxygen they produce carbon dioxide and water.

(a) Write an equation for the complete combustion of propane in oxygen.

___________________________________________________________________ (1)

(b) An expression can be derived using bond enthalpy data to estimate the enthalpy of combustion (ΔcH) of an alkane.

For an alkane with n carbon atoms: ΔcH = − (496n + 202) kJ mol−1

The enthalpy of combustion of an alkane was calculated to be −6650 kJ mol−1 using this expression.

Deduce the molecular formula of this alkane.

Show your working.

Molecular formula of alkane _________________________________________ (2)

(c) Suggest one reason, other than the use of mean bond enthalpies, why a value for the enthalpy of combustion of a liquid alkane is different from the value obtained using the expression in part (b)

___________________________________________________________________

___________________________________________________________________ (1)

(d) Values of the enthalpy change for combustion of 1 g of some alkanes are shown in the table.

methane ethane propane butane pentane

Enthalpy change in kJ for combustion of 1 g

−55.6 −52.0 −49.6 −48.7

Plot the enthalpy change for the combustion of 1 g against the number of carbon atoms in the alkanes in the table.

Draw a best fit line and use this to estimate the enthalpy change for combustion of 1 g of propane.

of 69

Write your answer in the table.

(3)

(e) Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in cars.

When isooctane is burned, the enthalpy change is −47.8 kJ g−1

Isooctane is a liquid at room temperature with a density of 0.692 g cm−3

Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in excess oxygen.

Give your answer to the appropriate number of significant figures.

of 69

Heat energy released ____________________ kJ (2)

(Total 9 marks)

Q2. Which equation is a propagation step in the conversion of trichloromethane into tetrachloromethane by reaction with chlorine in the presence of ultraviolet light?

A CHCl3 + Cl2 ⟶ CCl4 + HCl

B ●CCl3 + ●Cl ⟶ CCl4

C CHCl3 + ●Cl ⟶ CCl4 + ●H

D ●CCl3 + Cl2 ⟶ CCl4 + ●Cl (Total 1 mark)

Q3. The table shows possible conditions and products for the cracking of alkanes.

Which row is correct?

Type of cracking Conditions Products

A Thermal High pressure High temperature

Mainly alkanes

B Thermal Slight pressure High temperature

Mainly alkenes

C Catalytic Slight pressure High temperature

Mainly branched alkanes and aromatics

D Catalytic High pressure High temperature

Mainly branched alkanes and aromatics

(Total 1 mark)

Q4. Avgas is an aviation fuel used in the internal combustion engines of helicopters. It consists of a large number of hydrocarbons, including a high proportion of hexane, which can exist as several isomers.

(a) Draw the skeletal formulae of two branched isomers of hexane.

of 69

(1)

(b) State the type of isomerism shown by these branched isomers.

___________________________________________________________________ (1)

(c) Safety signs on the fuselage of the helicopter state that the air inlets to the engine need to be cleaned out regularly.

Write an equation for the combustion of hexane that would happen in the helicopter engine if the air inlets were partially blocked with debris.

___________________________________________________________________ (2)

(d) Suggest how this partial blockage might affect the performance of the helicopter engine.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(Total 5 marks)

Q5. Which catalyst is used in the catalytic cracking of alkanes?

A Concentrated phosphoric acid

B Iron

C Nickel

D Zeolite (Total 1 mark)

Q6. Which correctly represents an incomplete combustion of pentane?

A C5H12 + 8O2 ⟶ 5CO2 + 6H2O

B C5H12 + 8O2 ⟶ 4CO + CO2 + 6H2O

C C5H12 + 6O2 ⟶ 4CO + CO2 + 6H2O

D C5H12 + 5O2 ⟶ 4CO + CO2 + 4H2O + 2H2

(Total 1 mark)

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Q7. Which species is produced in a propagation step during the reaction of propane with an excess of chlorine in the presence of UV light?

A H•

B C3H5Cl

C C3H6CL2

D C6H14

(Total 1 mark)

Q8. Dodecane (C12H26) is a hydrocarbon found in the naphtha fraction of crude oil. Dodecane can be used as a starting material to produce a wide variety of useful products. The scheme below shows how one such product, polymer Y, can be produced from dodecane.

(a) Name the homologous series that both C2H4 and C4H8 belong to. Draw a functional group isomer of C4H8 that does not belong to this homologous series.

Name _____________________________________________________________

Functional group isomer

(2)

(b) Identify compound X.

___________________________________________________________________ (1)

(c) Name polymer Y.

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___________________________________________________________________ (1)

(d) Reaction 1 is an example of thermal cracking and is carried out at a temperature of 750 °C.

State one other reaction condition needed.

___________________________________________________________________ (1)

(e) Reaction 2 is exothermic. A typical compromise temperature of 200 °C is used industrially for this reaction.

Explain the effect of a change of temperature on both the position of equilibrium and the rate of reaction, and justify why a compromise temperature is used industrially.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(Total 11 marks)

Q9. Which of these substances does not contribute to the greenhouse effect?

A Unburned hydrocarbons.

B Carbon dioxide.

C Water vapour.

D Nitrogen. (Total 1 mark)

Q10. Which molecule is not produced when ethane reacts with bromine in the presence of

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ultraviolet light?

A C2H4Br2

B HBr

C H2

D C4H10

(Total 1 mark)

Q11. (a) Alite must be made at temperatures above 1250 ºC. This means that Portland

cement manufacture is a very energy-intensive process.

In the 1950s, heavy fuel oil was used. A typical heavy fuel oil contains compounds with the molecular formula C20H42. This kind of fuel requires pre-heating before it can be burned. The equation for the complete combustion of C20H42 is

2C20H42(g) + 61O2(g) → 40CO2(g) + 42H2O(g)

(i) Suggest why combustion of the fuel oil is likely to be incomplete.

______________________________________________________________ (1)

(ii) The large volume of exhaust gases can cause dust to be blown out of the kiln. The amount of dust can be decreased by passing the exhaust gases through electrostatic precipitators. These can produce sparks because of the high voltage.

Identify a gas that may be present because of incomplete combustion. Suggest why the use of electrostatic precipitators could be a hazard if this gas were present.

Identity of gas __________________________________________________

Reason _______________________________________________________ (2)

(iii) Cold air is blown over the alite at the end of the process so that it is cooled as quickly as possible.

Suggest how the resulting air can be used to improve the economy of the whole process.

______________________________________________________________

______________________________________________________________ (1)

(b) Cement kilns were once one of the largest contributors to global pollution by nitrogen oxides.

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(i) State how nitrogen oxides could be formed during the manufacture of Portland cement.

______________________________________________________________

______________________________________________________________ (1)

(ii) Sulfur dioxide is formed by the oxidation of sulfur compounds in the fuel used to heat the kiln. Sulfur dioxide can be removed by the minerals in the kiln. Suggest why a kiln with a very fast air flow is likely to emit more sulfur dioxide than one with a slower air flow but otherwise operating under the same conditions.

______________________________________________________________

______________________________________________________________ (1)

(Total 6 marks)

Q12. Octane and isooctane are structural isomers with the molecular formula C8H18. The displayed formulas and boiling points of octane and isooctane are shown in Figure 1.

Figure 1

(a) Give the IUPAC name for isooctane.

___________________________________________________________________ (1)

(b) Octane and isooctane can be separated in the laboratory.

Name a laboratory technique that could be used to separate isooctane from a mixture of octane and isooctane.

Outline how this technique separates isooctane from octane.

Name _____________________________________________________________

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Outline ____________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) Isooctane is added to petrol to increase its octane rating. Some high-performance engines require fuel with a higher octane rating.

Write an equation for the complete combustion of isooctane. Use the molecular formula (C8H18) of isooctane in your equation.

___________________________________________________________________ (1)

(d) Explain, in general terms, how a catalyst works.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(e) Carbon monoxide is produced when incomplete combustion takes place in engines. Nitrogen monoxide is another pollutant produced in car engines.

Write an equation to show how these pollutants react together in a catalytic converter.

___________________________________________________________________ (1)

(f) Platinum, palladium and rhodium are metals used inside catalytic converters. A very thin layer of the metals is used on a honeycomb ceramic support.

Explain why a thin layer is used in this way.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(g) Oleic acid (C18H34O2) is a straight-chain fatty acid obtained from plant oils. Isooctane can be made from oleic acid. The skeletal formula of oleic acid is shown in Figure 2.

Figure 2

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Identify a reagent that could be used in a chemical test to show that oleic acid is unsaturated.

State what would be observed in this test.

Reagent ___________________________________________________________

Observation _________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q13. Sulfur dioxide (SO2) is produced when some fossil fuels are burned.

Which of the following statements is true?

A Sulfur dioxide can be removed from waste gases in a power station by an acid-base reaction with calcium oxide.

B Sulfur dioxide is insoluble in water.

C Sulfur dioxide is a basic oxide.

D Sulfur dioxide is an ionic compound. (Total 1 mark)

Q14. Tetradecane (C14H30) is an alkane found in crude oil. When tetradecane is heated to a high temperature, one molecule of tetradecane decomposes to form one molecule of hexane and three more molecules.

Which of the following could represent this reaction?

A C14H30 → C6H14 + C4H8 + 2C2H4

B C14H30 → C6H14 + C6H12 + C2H4

C C14H30 → C5H12 + 3C3H6

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D C14H30 → C6H14 + C2H6 + 2C3H6

(Total 1 mark)

Q15. (a) Octane (C8H18) is an important compound in petrol.

(i) Identify the homologous series to which octane belongs.

______________________________________________________________ (1)

(ii) Write an equation to show the complete combustion of C8H18

______________________________________________________________ (1)

(iii) An isomer of octane used to improve the performance of car engines is shown.

Give the IUPAC name of this isomer.

______________________________________________________________ (1)

(b) Compound X is produced when an alkane is cracked.

(i) Give the IUPAC name for compound X.

______________________________________________________________ (1)

(ii) One molecule of an alkane is cracked to produce one molecule of compound X, one molecule of octane and one molecule of ethene.


______________________________________________________________ (1)

(iii) Name the type of cracking that produces a high yield of compound X. Give two conditions required for this process.

Type of cracking ________________________________________________

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Conditions _____________________________________________________

______________________________________________________________ (2)

(iv) Compound X has several isomers. The structure of X is repeated here.

Draw the displayed formula of a chain isomer, a position isomer and a functional group isomer of compound X.

Type of isomer Displayed formula of isomer of compound X

Chain

Position

Functional group


Q16. Haloalkanes are used as refrigerants, solvents and anaesthetics.

(a) Trichloromethane (CHCl3) is a haloalkane that can be formed by heating a mixture of chloromethane (CH3Cl) and chlorine.

(i) Write an overall equation for the formation of trichloromethane by the reaction of chloromethane with chlorine.

______________________________________________________________ (1)

(ii) Name the mechanism for this formation of trichloromethane.

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______________________________________________________________ (1)

(iii) Dichloromethane (CH2Cl2) is an intermediate in this formation of trichloromethane.

Write an equation for each of the following steps in the mechanism for the reaction of dichloromethane with chlorine.

Initiation step

______________________________________________________________


______________________________________________________________


______________________________________________________________

A termination step leading to the formation of a compound with formula C2H2Cl4

______________________________________________________________ (4)

(b) Chlorotrifluoromethane (CClF3) is used as a refrigerant, but is being phased out due to concerns about ozone depletion in the upper atmosphere. In the upper atmosphere, CClF3 decomposes in the presence of UV light forming a reactive intermediate that catalyses the decomposition of ozone.

(i) Write an equation to show how CClF3 decomposes to form the reactive intermediate.

______________________________________________________________ (1)

(ii) Write two equations to show how this reactive intermediate is involved in catalysing the decomposition of ozone.

1. ____________________________________________________________

2. ____________________________________________________________ (2)

(Total 9 marks)

Q17. Central heating fuel, obtained by the fractional distillation of crude oil, contains saturated hydrocarbons with the molecular formula C16H34

(a) Give the meaning of the terms saturated and hydrocarbon as applied to saturated hydrocarbons.

Saturated __________________________________________________________

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___________________________________________________________________

Hydrocarbon ________________________________________________________

___________________________________________________________________ (2)

(b) If the boiler for a central heating system is faulty, a poisonous gas may be produced during the combustion of C16H34

Write an equation for the reaction that forms this poisonous gas and one other product only.

___________________________________________________________________ (1)

(c) Explain why the sulfur compounds found in crude oil should be removed from the fractions before they are used for central heating fuel.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) A hydrocarbon C16H34 can be cracked to form C8H18, ethene and propene.

(i) Write an equation to show this cracking reaction.

______________________________________________________________ (1)

(ii) Suggest one important substance manufactured on a large scale from propene.

______________________________________________________________ (1)

(iii) Draw the displayed formula of the functional group isomer of propene.

(1)

(e) There are many structural isomers with the molecular formula C8H18

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Draw the structure of 2,3,3-trimethylpentane.

(1)

(f) A compound C8H18 reacts with chlorine to give several haloalkanes.

Give the IUPAC name of the following haloalkane.

___________________________________________________________________ (1)

(Total 10 marks)

Q18. Trifluoromethane (CHF3) can be used to make the refrigerant chlorotrifluoromethane(CClF3).

(a) Chlorotrifluoromethane is formed when trifluoromethane reacts with chlorine.

CHF3 + Cl2 CClF3 + HCl

The reaction is a free-radical substitution reaction similar to the reaction of methane with chlorine.

(i) Write an equation for each of the following steps in the mechanism for the reaction of CHF3 with Cl2

Initiation step

______________________________________________________________


______________________________________________________________

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______________________________________________________________

Termination step to form hexafluoroethane

______________________________________________________________ (4)

(ii) Give one essential condition for this reaction.

______________________________________________________________ (1)

(b) In some refrigeration systems, CHF3 has replaced CClF3 because of concerns about ozone depletion.

(i) Identify the species formed from CClF3 that is responsible for the catalytic decomposition of ozone in the upper atmosphere.

______________________________________________________________ (1)

(ii) Write an overall equation to represent the decomposition of ozone into oxygen.

______________________________________________________________ (1)

(Total 7 marks)

Q19. Chlorine can be used to make chlorinated alkanes such as dichloromethane.

(a) Write an equation for each of the following steps in the mechanism for the reaction of chloromethane (CH3Cl) with chlorine to form dichloromethane (CH2Cl2).

Initiation step

___________________________________________________________________


___________________________________________________________________


___________________________________________________________________

The termination step that forms a compound with empirical formula CH2Cl.

___________________________________________________________________

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(4)

(b) When chlorinated alkanes enter the upper atmosphere, carbon-chlorine bonds are broken. This process produces a reactive intermediate that catalyses the decomposition of ozone. The overall equation for this decomposition is

2O3 3O2

(i) Name the type of reactive intermediate that acts as a catalyst in this reaction.

______________________________________________________________ (1)

(ii) Write two equations to show how this intermediate is involved as a catalyst in them decomposition of ozone.

Equation 1 ____________________________________________________

Equation 2 ____________________________________________________ (2)

(Total 7 marks)

Q20. The following table shows the boiling points of some straight-chain alkanes.

CH4 C2H6 C3H8 C4H10 C5H12

Boiling point / °C −162 −88 −42 −1 36

(a) State a process used to separate an alkane from a mixture of these alkanes.

___________________________________________________________________ (1)

(b) Both C3H8 and C4H10 can be liquefied and used as fuels for camping stoves.

Suggest, with a reason, which of these two fuels is liquefied more easily.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(c) Write an equation for the complete combustion of C4H10

___________________________________________________________________ (1)

(d) Explain why the complete combustion of C4H10 may contribute to environmental problems.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (1)

(e) Balance the following equation that shows how butane is used to make the compound called maleic anhydride.

..........CH3CH2CH2CH3 + .......... O2 ..........C2H2(CO)2O + .......... H2O (1)

(f) Ethanethiol (C2H5SH), a compound with an unpleasant smell, is added to gas to enable leaks from gas pipes to be more easily detected.

(i) Write an equation for the combustion of ethanethiol to form carbon dioxide, water and sulfur dioxide.

______________________________________________________________ (1)

(ii) Identify a compound that is used to react with the sulfur dioxide in the products of combustion before they enter the atmosphere.

Give one reason why this compound reacts with sulfur dioxide.

Substance ____________________________________________________

Reason _______________________________________________________

______________________________________________________________ (2)

(iii) Ethanethiol and ethanol molecules have similar shapes.

Explain why ethanol has the higher boiling point.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(g) The following compound X is an isomer of one of the alkanes in the table on above.

(i) Give the IUPAC name of X.

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______________________________________________________________ (1)

(ii) X has a boiling point of 9.5 °C.

Explain why the boiling point of X is lower than that of its straight-chain isomer.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(iii) The following compound Y is produced when X reacts with chlorine.

Deduce how many other position isomers of Y can be formed. Write the number of other position isomers in this box.

(1)

(h) Cracking of one molecule of an alkane Z produces one molecule of ethane, one molecule of propene and two molecules of ethene.

(i) Deduce the molecular formula of Z.

______________________________________________________________ (1)

(ii) State the type of cracking that produces a high proportion of ethene and propene. Give the two conditions for this cracking process.

Type of cracking ________________________________________________

Conditions _____________________________________________________

______________________________________________________________ (2)

(Total 17 marks)

Q21. Compound X is shown below. It is a member of a homologous series of hydrocarbons.

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(a) (i) Deduce the general formula of the homologous series that contains X.

______________________________________________________________ (1)

(ii) Name a process used to obtain a sample of X from a mixture containing other members of the same homologous series.

______________________________________________________________ (1)

(b) There are several isomers of X.

(i) Give the IUPAC name of the position isomer of X.

______________________________________________________________ (1)

(ii) Draw the structure of a functional group isomer of X.

(1)

(c) At high temperatures, one molecule of C15H32 can be converted into two molecules of X and one molecule of another compound.

(i) Write an equation for this reaction.

______________________________________________________________ (1)

(ii) State the name of the process used to obtain a high yield of X from C15H32 Give one reason why this process is used in industry.

Name _________________________________________________________

Reason _______________________________________________________

______________________________________________________________ (2)

(iii) State why high temperatures are needed for this process.

______________________________________________________________

______________________________________________________________

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(1)

(d) Compound X can be converted into compound Y. Compound Y is shown below.

(i) Suggest the formula of a reagent that could be added to X in order to convert it into Y.

______________________________________________________________ (1)

(ii) Give one use of Y.

______________________________________________________________ (1)

(iii) Write an equation to show the reaction of Y in a limited supply of air to produce a solid and water only.

______________________________________________________________ (1)

(iv) When a sample of Y, contaminated with CH3SH, is burned completely in air, a toxic gas is formed. Identify this toxic gas and suggest a compound that could be used to remove the toxic gas from the products of combustion.

Toxic gas ______________________________________________________

Compound used to remove toxic gas ________________________________

______________________________________________________________ (2)

(v) Suggest the name of the process that occurs when the toxic gas in part (d)(iv) is removed.

______________________________________________________________ (1)

(e) Explain why the boiling points of X and Y are similar.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

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(Total 16 marks)

Q22. Hexane (C6H14) is a member of the homologous series of alkanes.

(a) (i) Name the raw material from which hexane is obtained.

______________________________________________________________ (1)

(ii) Name the process used to obtain hexane from this raw material.

______________________________________________________________ (1)

(b) C6H14 has structural isomers.

(i) Deduce the number of structural isomers with molecular formula C6H14

Write the number in this box.

(Space for working)

(1)

(ii) State one type of structural isomerism shown by the isomers of C6H14

______________________________________________________________ (1)

(c) One molecule of an alkane X can be cracked to form one molecule of hexane and two molecules of propene.

(i) Deduce the molecular formula of X.

______________________________________________________________

______________________________________________________________ (1)

(ii) State the type of cracking that produces a high percentage of alkenes. State the conditions needed for this type of cracking.

Type of cracking ________________________________________________

Conditions _____________________________________________________

______________________________________________________________ (2)

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(iii) Explain the main economic reason why alkanes are cracked.

______________________________________________________________

______________________________________________________________ (1)

(d) Hexane can react with chlorine under certain conditions as shown in the following equation.

C6H14 + Cl2 C6H13Cl + HCl

(i) Both the products are hazardous. The organic product would be labelled ‘flammable'. Suggest the most suitable hazard warning for the other product.

______________________________________________________________ (1)

(ii) Calculate the percentage atom economy for the formation of C6H13Cl (Mr = 120.5) in this reaction.

______________________________________________________________

______________________________________________________________ (1)

(e) A different chlorinated compound is shown below. Name this compound and state its empirical formula.

Name ____________________________________________________________

Empirical formula ___________________________________________________ (2)

(Total 12 marks)

Q23. (a) There is a risk of gas explosions in coal mines. This risk is mainly due to the

presence of methane. If the percentage of coal-mine methane (CMM) in the air in the mine is greater than 15%, the explosion risk is much lower. CMM slowly escapes from the mine into the atmosphere.

Write an equation to show the complete combustion of methane.

Suggest one reason why there is a much lower risk of an explosion if the percentage of CMM is greater than 15%.

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State why it is beneficial to the environment to collect the CMM rather than allowing it to escape into the atmosphere.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) _______________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Methane can be obtained from crude oil. Some of this crude oil contains an impurity called methanethiol (CH3SH). This impurity causes environmental problems when burned.

Write an equation to show the complete combustion of methanethiol.

State why calcium oxide can be used to remove the sulfur-containing product of this combustion reaction.

State one pollution problem that is caused by the release of this sulfur-containing product into the atmosphere.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 6 marks)

Q24. Alkanes are used as fuels. A student burned some octane (C8H18) in air and found that the combustion was incomplete.

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(a) (i) Write an equation for the incomplete combustion of octane to produce carbon monoxide as the only carbon-containing product.

______________________________________________________________ (1)

(ii) Suggest one reason why the combustion was incomplete.

______________________________________________________________

______________________________________________________________ (1)

(b) Catalytic converters are used to remove the toxic gases NO and CO that are produced when alkane fuels are burned in petrol engines.

(i) Write an equation for a reaction between these two toxic gases that occurs in a catalytic converter when these gases are removed.

______________________________________________________________ (1)

(ii) Identify a metal used as a catalyst in a catalytic converter. Suggest one reason, other than cost, why the catalyst is coated on a ceramic honeycomb.

Metal _________________________________________________________

Reason _______________________________________________________

______________________________________________________________ (2)

(c) If a sample of fuel for a power station is contaminated with an organic sulfur compound, a toxic gas is formed by complete combustion of this sulfur compound.

(i) State one environmental problem that can be caused by the release of this gas.

______________________________________________________________

______________________________________________________________ (1)

(ii) Identify one substance that could be used to remove this gas. Suggest one reason, other than cost, why this substance is used.

Substance _____________________________________________________

Reason why used _______________________________________________

______________________________________________________________ (2)

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(Total 8 marks)

Q25. Pentane is a member of the alkane homologous series.

(a) Give the general formula for the homologous series of alkanes.

___________________________________________________________________ (1)

(b) One of the structural isomers of pentane is 2,2-dimethylpropane.

Draw the displayed formula of 2,2-dimethylpropane.

State the type of structural isomerism shown.

___________________________________________________________________ (2)

(c) A molecule of hydrocarbon Y can be thermally cracked to form one molecule of pentane and two molecules of ethene only.

Deduce the molecular formula of Y.

State why high temperatures are necessary for cracking reactions to occur.

Give one reason why thermal cracking reactions are carried out in industry.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) _______________________________________________________

___________________________________________________________________

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___________________________________________________________________ (3)

(d) Write an equation for the incomplete combustion of pentane to form a solid pollutant.

Suggest why this solid pollutant is an environmental problem.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) _______________________________________________________

___________________________________________________________________ (2)

(e) Pentane can react with chlorine as shown in the following equation.

C5H12 + Cl2 → C5H11Cl + HCl

Calculate the percentage atom economy for the formation of C5H11Cl

Deduce how many straight-chain isomers of C5H11Cl could be formed.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(f) Consider the following compound.

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Name this compound.

Deduce the empirical formula of this compound.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 13 marks)

Q26. Halogens are used to make halogenated organic compounds.

(a) The refrigerant used in air conditioners is a mixture of fluorinated alkanes. These compounds are made by fluorination reactions. The mechanism for the reaction of fluorine with an alkane or with a fluoroalkane is a free-radical substitution similar to the reaction of chlorine with methane.

(i) Write the overall equation for the reaction of fluorine with methane to form trifluoromethane (CHF3).

______________________________________________________________ (1)

(ii) Write equations for the following steps in the mechanism for the reaction of fluorine with trifluoromethane (CHF3) to form tetrafluoromethane (CF4).

Initiation step

______________________________________________________________


______________________________________________________________


______________________________________________________________

A termination step leading to the formation of hexafluoroethane.

______________________________________________________________ (4)

(b) Chlorofluorocarbons (CFCs) were used as refrigerants. In the upper atmosphere, ultra-violet radiation breaks bonds in the CFCs to produce a reactive intermediate that catalyses the decomposition of ozone.

(i) An example of a CFC is 1,1,1-trichloro-2,2-difluoroethane. Draw the displayed formula of this CFC.

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(1)

(ii) Identify a bond in a CFC that is broken by ultra-violet radiation to produce a reactive intermediate. Give the name of this reactive intermediate that catalyses the decomposition of ozone. Write an overall equation for this decomposition of ozone.

Bond broken ____________________________________________________

Name of the reactive intermediate ___________________________________

Overall equation

______________________________________________________________ (3)

(Total 9 marks)

Q27. There are several oxides of nitrogen.

(a) An oxide of nitrogen contains 25.9% by mass of nitrogen. Determine the empirical formula of this oxide.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Give one reason why the oxide NO is a pollutant gas.

___________________________________________________________________

___________________________________________________________________ (1)

(c) The oxide NO reacts with oxygen to form nitrogen dioxide. Write an equation for this reaction.

___________________________________________________________________ (1)

(d) Explain how NO is produced in the engine of a motor vehicle.

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(e) Write an equation to show how NO is removed from the exhaust gases in motor vehicles using a catalytic converter.

___________________________________________________________________ (1)

(Total 8 marks)

Q28. The alkane butane is used as a fuel.

(a) (i) Write an equation for the complete combustion of butane.

______________________________________________________________ (1)

(ii) State a condition which may cause carbon to be formed as a product in the combustion of butane.

______________________________________________________________ (1)

(b) Butane obtained from crude oil may contain trace amounts of an impurity. When this impurity burns it produces a toxic gas that can be removed by reacting it with calcium oxide coated on a mesh.

(i) Suggest the identity of the toxic gas.

______________________________________________________________ (1)

(ii) Suggest why calcium oxide reacts with the toxic gas.

______________________________________________________________ (1)

(iii) Suggest why the calcium oxide is coated on a mesh.

______________________________________________________________ (1)

(Total 5 marks)

Q29. Pent-1-ene is a member of the alkene homologous series.

(a) Pent-1-ene can be separated from other alkenes.

State the physical property of alkenes that allows them to be separated from a

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mixture by fractional distillation.

___________________________________________________________________ (1)

(b) (i) State the meaning of the term structural isomerism.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) Name the branched chain isomer of pent-1-ene shown below.

______________________________________________________________ (1)

(iii) Draw the structure of a functional group isomer of pent-1-ene.

(1)

(c) The cracking of one molecule of compound X produces pent-1-ene, ethene and butane in a 1:2:1 mol ratio. Deduce the molecular formula of X and state a use for the ethene formed.

Molecular formula of X ________________________________________________

___________________________________________________________________

Use of ethene _______________________________________________________ (2)

(Total 7 marks)

Q30. Alkanes are saturated hydrocarbons which can be obtained from crude oil. Pentane is an example of an alkane. A molecule of pentane contains five carbon atoms.

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(a) (i) State the meaning of the term saturated and of the term hydrocarbon as applied to alkanes.

Saturated ______________________________________________________

______________________________________________________________

Hydrocarbon ___________________________________________________

______________________________________________________________ (2)

(ii) Give the general formula for the alkanes.

______________________________________________________________ (1)

(b) Pentane burns completely in oxygen.


______________________________________________________________ (1)

(ii) State how the products of this reaction may affect the environment.

______________________________________________________________

______________________________________________________________ (1)

(c) Give the name of a solid pollutant which may form when pentane burns incompletely in air.

___________________________________________________________________ (1)

(d) One molecule of C9H20 can be cracked to form one molecule of pentane and one other product.

(i) Write an equation for this cracking reaction.

______________________________________________________________ (1)

(ii) Suggest a type of compound that can be manufactured from the other product of this cracking reaction.

______________________________________________________________

______________________________________________________________

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(1)

(iii) State why a high temperature is needed for cracking reactions to occur.

______________________________________________________________

______________________________________________________________ (1)

(e) Pentane can react to form the following haloalkane Q.

(i) Name Q.

______________________________________________________________ (1)

(ii) State the type of structural isomerism shown by Q and the haloalkane shown below.

______________________________________________________________ (1)

(Total 11 marks)

Q31. Petrol contains saturated hydrocarbons. Some of the molecules in petrol have the molecular formula C8H18 and are referred to as octanes. These octanes can be obtained from crude oil by fractional distillation and by cracking suitable heavier fractions.

Petrol burns completely in a plentiful supply of air but can undergo incomplete combustion in a car engine.

(a) State the meaning of both the words saturated and hydrocarbon as applied to the term saturated hydrocarbon.

Name the homologous series to which C8H18 belongs.

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(c) C8H18 is obtained by the catalytic cracking of suitable heavy fractions. State what is meant by the term cracking and name the catalyst used in catalytic cracking.

Write an equation to show how one molecule of C14H30 is cracked to form one molecule of C8H18 and one molecule of another hydrocarbon.

Explain why oil companies need to crack ‘suitable heavy fractions’.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(d) Write an equation for the incomplete combustion of C8H18 to form carbon monoxide and water only.

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A catalytic converter is used to remove carbon monoxide from the exhaust gases in a car. Identify a catalyst used in the catalytic converter.

Write an equation to show how carbon monoxide is removed in a catalytic converter.

State why the water produced in the exhaust gases may contribute to global warming.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(e) When some petrol was accidentally contaminated in 2007, the sensors in the affected cars caused a decrease in the supply of petrol to the engine.

Suggest the effect that the contaminated fuel would have on the performance of the cars.

State how the oil company might have recognised the problem before the petrol was sold.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(f) The molecular formula C8H18 represents several structural isomers.

State what is meant by the term structural isomers.

Name the following structural isomer of C8H18

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 20 marks)

Q32. (a) Hexane (C6H14) is a hydrocarbon which is a component of LPG (liquid petroleum

gas), used as a fuel for heating. When burning fuels in boilers it is important to ensure complete combustion.

(i) Give two reasons why boilers are designed to ensure complete combustion.

Reason 1 ______________________________________________________

______________________________________________________________

Reason 2 ______________________________________________________

______________________________________________________________

(ii) Write an equation for the incomplete combustion of hexane.

______________________________________________________________

(iii) Suggest how an engineer or a chemist could demonstrate that the combustion of hexane in a faulty boiler was incomplete.

______________________________________________________________ (5)

(b) Branched chain alkanes are often preferred as fuels. Draw the structure of two branched chain isomers of hexane and name the first isomer.

Isomer 1 Isomer 2

Name of isomer 1 ____________________________________________________ (3)

(c) Hexane can be cracked in the presence of a catalyst to produce another hydrocarbon, Z, and methane.

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(i) Draw a possible structure for Z.

(ii) Give a suitable catalyst for this reaction.

______________________________________________________________

(iii) Suggest why the product Z has more commercial value than hexane.

______________________________________________________________

______________________________________________________________ (3)

(d) The overall equation for the production of dichloromethane from methane and chlorine is shown below.

CH4 + 2Cl2 → CH2Cl2 + 2HCl

(i) Calculate the % atom economy for the formation of CH2Cl2 in this reaction.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(ii) Give one reason why this atom economy of less than 100% is an important consideration for the commercial success of this process and predict how a chemical company would maximise profits from this process.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(Total 14 marks)

Q33. The fractions obtained from petroleum contain saturated hydrocarbons that belong to the homologous series of alkanes.

(a) Any homologous series can be represented by a general formula.

(i) State two other characteristics of homologous series.

Characteristic 1 _________________________________________________

______________________________________________________________

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Characteristic 2 _________________________________________________

______________________________________________________________

(ii) Name the process which is used to obtain the fractions from petroleum.

______________________________________________________________

(iii) State what is meant by the term saturated, as applied to hydrocarbons.

______________________________________________________________

______________________________________________________________ (4)

(b) Decane has the molecular formula C10H22

(i) State what is meant by the term molecular formula.

______________________________________________________________

______________________________________________________________

(ii) Give the molecular formula of the alkane which contains 14 carbon atoms.

______________________________________________________________

(iii) Write an equation for the incomplete combustion of decane, C10H22, to produce carbon and water only.

______________________________________________________________ (3)

(c) When petrol is burned in an internal combustion engine, some nitrogen monoxide, NO, is formed. This pollutant is removed from the exhaust gases by means of a reaction in a catalytic converter.

(i) Write an equation for the reaction between nitrogen and oxygen to form nitrogen monoxide.

______________________________________________________________

(ii) Identify a catalyst used in a catalytic converter.

______________________________________________________________

(iii) Write an equation to show how nitrogen monoxide is removed from the exhaust gases as they pass through a catalytic converter.

______________________________________________________________ (3)

(Total 10 marks)

Q34. Chlorination of ethane follows a free-radical substitution mechanism. This mechanism is similar to that which occurs when methane is chlorinated. The overall equation for the

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reaction of ethane to form chloroethane is given below.

C2H6 + Cl2 C2H5Cl + HCl

State the conditions and outline a mechanism for this reaction. Show how butane can be formed in this reaction.

(Total 5 marks)

Q35. (a) Dichloromethane, CH2Cl2, is one of the products formed when chloromethane,

CH3Cl, reacts with chlorine.

(i) Name the type of mechanism involved in this reaction and write an equation for each of the steps named below.

Name of type of mechanism _______________________________________

Initiation step

______________________________________________________________


______________________________________________________________


______________________________________________________________

(ii) Write an overall equation for the formation of dichloromethane from chloromethane.

______________________________________________________________ (5)

(b) A compound contains 10.1% carbon and 89.9% chlorine by mass. Calculate the molecular formula of this compound, given that its relative molecular mass (Mr) is 237.0

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) Suggest the formulae of two bromine-containing organic compounds formed when dibromomethane, CH2Br2, reacts with bromine.

Compound 1 _________________________________________________________

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Compound 2 _________________________________________________________


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Mark schemes

Q1. (a) C3H8 + 5O2 ⟶ 3CO2 + 4H2O

allow fractions / multiples allow any correct structural representation of molecules ignore state symbols

1

(b) M1 working that leads to n = 13 e.g. −6650 = −(496n + 202) and/or 496n = 6650 − 202 and/or 496n = 6448 (n = 13)

1

M2 C13H28

C13H28 scores M1 and M2 if some correct working shown C13H28 with no working scores M2 only allow error carried forward for M2 for a correct formula of an alkane from the value of n worked out for M1 (but there must be some working shown leading to this incorrect value of n); for example, allow C14H30 if error in M1 stemming from error in rearranging equation

1

(c) Idea that • alkane is not gaseous or • equation relates to gaseous alkanes or • it takes energy to convert it into a gas or • that water / alkane / substances are gaseous in calculations using bond enthalpies

ignore references to heat loss, incomplete combustion, loss of evaporation, not being in standard conditions or that it is not standard state

1

(d) M1 plotting the four values correctly (allow one error where point is ±1 square out)

If plotted points for wrong number of C atoms for two or more compounds, cannot score M1 or M2, but could score M3 if read value off for 3C atoms

1 M2 smooth best fit curve

M2 best fit curve for their four points for the correct number of C atoms

1 M3 value from their best fit line for 3 C atoms (allow ± 1 square)

M3 need – sign (but ignore units); cannot score M3 unless there is a line on the graph

1

(e) M1 mass of isooctane = 692 (g)

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correct answer scores M1 and M2 1

M2 3.31 × 104 or 33100 (kJ) (3sf only) M2 correct value to incorrect number of sig figs is 1 mark; ignore sign ; no error carried forward for M2

1 [9]

Q2. D

[1]

Q3. C

[1]

Q4. (a) Any two of these isomers

1

(b) Chain isomerism Mark consequential to part (a)

1

(c) C6H14 + 6.5O2 ⟶ 6CO + 7H2O M1 Product is CO or C M2 Balanced equation

1

OR

C6H14 + 3.5O2 6C + 7H2O Allow equations containing CO2 as long as either C, CO or both are also present

1

(d) Less energy given out by the fuel / engine is less powerful / less efficient / needs to burn more fuel to get the same energy / increased costs due to need to use more fuel

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Do not allow answers linked to CO poisoning or incomplete combustion

1 [5]

Q5. D

[1]

Q6. C

[1]

Q7. C

[1]

Q8. (a) Alkenes

1

Correctly drawn molecule of cyclobutane or methyl cyclopropane, need not be displayed formula

1

(b) C6H14 (or correct alkane structure with 6 carbons) Allow hexane or any other correctly named alkane with 6 carbons

1

(c) Poly(but-2-ene) 1

(d) High pressure Allow pressure � MPa Mention of catalyst loses the mark

1

(e) This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question.

Level 3

All stages are covered and the explanation of each stage is generally correct

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and virtually complete.

Answer communicates the whole process coherently and shows a logical progression from stage 1 and stage 2 (in either order) to stage 3.

5–6 marks

Level 2

All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete.

Answer is mainly coherent and shows progression. Some steps in each stage may be out of order and incomplete.

3–4 marks

Level 1

Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete.

Answer includes isolated statements but these are not presented in a logical order or show confused reasoning.

1–2 marks

Level 0

Insufficient correct chemistry to gain a mark. 0 marks

Indicative chemistry content Stage 1: consider effect of higher temperature on yield (Or vice versa for lower temperature) • Le Chatelier’s principle predicts that equilibrium shifts to oppose any increase in temperature • Exothermic reaction, so equilibrium shifts in endothermic direction / to the left • So a Higher T will reduce yield Stage 2: consider effect of higher temperature on rate (Or vice versa for lower temperature) • At higher temperature, more high energy molecules • more collisions have E>Ea • So rate of reaction increases / time to reach equilibrium decreases Stage 3: conclusion Industrial conditions chosen to achieve (cost-effective) balance of suitable yield at reasonable rate

[11]

Q9. D

[1]

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Q10. C

[1]

Q11. (a) (i) Difficult to supply sufficient air / oxygen (for complete combustion)

Accept ratio of oxygen to fuel is very high. Ignore any references to temperature factors.

1

(ii) Carbon monoxide (or unburned fuel) 1

Flammable / explosion 1

(iii) Used to pre-heat fuel or air in the kiln Raise steam to generate electricity used in the process.

1

(b) (i) Nitrogen reacts with oxygen at high temperature 1

(ii) Less chance of reaction of SO2 if the flow is fast Increased oxygen supply so more sulfur (compounds) oxidized. Allow less contact time between SO2 and the minerals.

1 [6]

Q12. (a) 2,2,4-trimethylpentane

This answer only but ignore punctuation 1

(b) M1 (fractional or simple) distillation Incorrect process in M1 CE=0 If M1 blank, mark on for M2 and M3 (ignore boiling, condensing)

1

M2 idea that isooctane / the one with the lower boiling point boils (first) (or reaches top of column first)

Ignore reference to octane boiling and being collected at higher temperature If temperature referred to, should be between 99 and 124°C “it” refers to isooctane M2 – allow vaporises/evaporates first

1

M3 idea that isooctane condenses / liquefies and collected Penalise M2 and M3 if octane boils first In M2 and M3 – if no specific reference to individual alkanes,

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could score one mark for M2 + M3 combined if M2 and M3 both otherwise correct M2 and M3 must refer to a laboratory apparatus (not to an industrial process)

1

(c) C8H18 + 12½O2 → 8CO2 + 9H2O Accept multiples; ignore state symbols Accept any correct structural representation of isooctane

1

(d) M1 Alternative route/mechanism/pathway 1

M2 With lower activation energy Accept Ea for activation energy

1

(e) 2CO + 2NO → 2CO2 + N2

Accept multiples; ignore state symbols 1

(f) M1 to reduce amount of metals needed / small amount of metal needed Relates to low amount of metal

1

M2 Increase / maximise / produce large surface area or to give catalyst a larger surface area: volume ratio or so that high(er) proportion of atoms/metal is on surface

Is related to large surface area 1

(g) M1 bromine (water or in organic solvent or CCl4) / Br2 (aq) / Br2

No reagent or an incorrect reagent (e.g. bromide), CE=0; Penalise Br (or incorrect formula of other correct reagent) but mark on for M2 It must be a whole reagent and/or correct formula If oxidation state given in name, it must be correct If ‘manganate’ or ‘manganate(IV)’ or incorrect formula, penalise M1 but mark on Ignore ‘acidified’

1

M2 (orange/yellow to) colourless / decolourised / loses its colour Ignore goes clear Ignore brown/red, but penalise other incorrect colours

1

Alternatives: M1 = potassium manganate(VII), M2 = colourless M1 = conc sulfuric acid, M2 = brown M1 = iodine, M2 = colourless

[12]

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Q13. A

[1]

Q14. A

[1]

Q15. (a) (i) Alkane(s)

Ignore CnH2n+2 1

(ii) C8H18 + 12.5O2 → 8CO2 + 9H2O Allow multiples

1

(iii) 2, 2, 4-trimethylpentane 1

(b) (i) But-1-ene Ignore (E or Z)

1

(ii) C14H30 1

(iii) Thermal If catalytic CE = 0

1

High pressure / 7000kPa / 70 atms and High temperature/temperature in range 400-1000°C (673–1273K)

(Allow ≥1000 kPa or ≥10 atms – no upper value) Allow high temperature and pressure or high pressure and temperature If no units for temperature allow 673-1000 Must show unambiguous structure Penalise lack of displayed formula once only

1

(iv) 1

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1

1

[10]

Q16. (a) (i) CH3Cl + 2Cl2 → CHCl3 + 2HCl

IGNORE state symbols ALLOW multiples

1 (ii) (Free-)radical substitution

This answer only 1

(iii) Initiation: Cl2 → 2Cl•

Penalise absence of dot once only 1

1st Propagation step Cl• + CH2Cl2 → •CHCl2 + HCl

Penalise + and/or – charges every time 1

2nd Propagation step •CHCl2 + Cl2 → CHCl3 + Cl•

ALLOW • anywhere on •CHCl2 but, if drawn out as a structure, then • must be on C

1

Termination 2 •CHCl2 → C2H2Cl4

Mark independently

ALLOW •CH2Cl + •CCl3 → C2H2Cl4

IGNORE state symbols throughout 1

(b) (i) CClF3 → •CF3 +Cl• ALLOW • anywhere on •CF3 unless displayed

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1

(ii) Cl• + O3 → ClO• + O2

Equations can be in either order Penalise absence of • once only

1

ClO• + O3 → 2O2 + Cl• ALLOW • anywhere on •ClO NOT •O3

1 [9]

Q17. (a) Saturated − single bonds only / no double bonds

1

Hydrocarbon − contains carbon and hydrogen (atoms) only 1

(b) C16H34 + 16.5O2 16CO + 17H2O Allow multiples

1

(c) (On combustion) SO2 produced Allow equation to produce SO2. Ignore sulfur oxides.

1

Which causes acid rain If formula shown it must be correct M2 is dependent on M1. But if M1 is sulfur oxides, allow M2. For M2 allow consequence of acid rain or SO2.

Ignore greenhouse effect and toxic 1

(d) (i) C16H34 C8H18 + C2H4 + 2C3H6

Allow multiples 1

(ii) polypropene / propan(-1 or 2-)ol / propane(-1,2-)diol / isopropanol / propanone / propanal

Accept alternative names Ignore plastic and polymer

1

(iii)

1

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(e)

Allow any unambiguous representation

1

(f) 2,4-dichloro-2,4-dimethylhexane Only but ignore punctuation

1 [10]

Q18. (a) (i) M1 Initiation

Cl2 2Cl• Penalise absence of dot once only.

M2 First propagation

Cl• + CHF3 CF3• +HCl Penalise + or − charges every time.

M3 Second propagation

Cl2 + CF3• CClF3 + Cl• Credit CF3• with the radical dot above / below / to either side.

M4 Termination (must make C2F6)

2 CF3• C2F6 or CF3CF3

Mark independently. 4

(ii) ultra-violet / uv / sun light

OR (very) high temperature

OR 500 °C ≤ T ≤ 1000 °C

OR 773 K ≤ T ≤ 1273 K 1

(b) (i) Cl• OR chlorine atom / chlorine (free−) radical / Cl (atom) Not ‘chlorine’ alone. Credit ‘Cl’ alone on this occasion.

1

(ii) 2O3 3O2

Or multiples. Ignore state symbols.

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If the correct answer is on the line OR clearly identified below some working, then ignore any working.

1 [7]

Q19. (a) Initiation

Cl2 2Cl• Penalise absence of dot once only.

First propagation Cl• + CH3Cl •CH2Cl + HCl

Credit the dot anywhere on the radical.

Second propagation Cl2 + •CH2Cl CH2Cl2 + Cl•

Termination (must make 1,2-dichloroethane) 2 •CH2Cl CH2ClCH2Cl

Penalise C2H4Cl2 4

(b) (i) (chlorine free) radical Ignore formula.

1

(ii) M1 Cl• + O3 ClO• + O2

M2 ClO• + O3 Cl• + 2O2

M1 and M2 could be in either order. Credit the dot anywhere on the radical. Penalise absence of dot once only. Individual multiples acceptable but both need to be doubled if two marks are to be awarded.

2 [7]

Q20. (a) Fractional distillation / fractionation / GLC / gas liquid chromatography

1

(b) C4H10

Need C4H10 and the reason for the mark

Because it has a higher bp / has stronger IMF / larger molecule / longer chain / larger surface (area)

1

(c) C4H10 + 6½ O2 4CO2 + 5H2O Accept multiples Ignore state symbols

1

(d) CO2 or H2O evolved is a greenhouse gas / CO2 or H2O evolved contribute to

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global warming / the products are greenhouse gases Ignore climate change

1

(e) CH3CH2CH2CH3 + 3.5O2 C2H2(CO)2O + 4H2O Accept multiples Allow with or without a number 1 before the organic molecules

1

(f) (i) C2H5SH + 4.5O2 2CO2 + 3H2O + SO2

Accept multiples 1

(ii) Calcium oxide / calcium carbonate Allow any base or alkali Allow correct formulae

1

Neutralises the SO2 / acid base reaction / it is a base Can only score M2 if base or alkali used in M1 Allow M2 if blank in M1

1

(iii) Ethanol contains hydrogen bonding Breaking covalent bonds CE = 0 / 2

Which is stronger than IMF (VDW / dipole-dipole forces) in ethanethiol / (H bonding) is the strongest IMF

Only award M2 if M1 given, but allow IMF in ethanol are stronger than in ethanethiol for maximum 1 mark

1

(g) (i) (2,2-)dimethylpropane Ignore punctuation

1

(ii) Because molecule is smaller / less polarisable / has less surface (area) / is more spherical / molecules can’t get as close to one another (to feel the vdW forces)

Allow converse answers referring to straight chain isomers CE = 0 / 2 if breaking bonds

1

vdW intermolecular forces or vdW force between molecules are weaker or fewer

Need vdW rather than just IMF 1

(iii) 1 or one 1

(h) (i) C9H20

H20C9 1

(ii) Thermal (cracking)

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If not thermal cracking CE = 0 / 2 1

High pressure AND high temperature If blank mark on Allow high P and T

1

OR

Pressure of ≥ 10 atm, ≥ 1 MPa ≥ 1000 kPa

AND temp of 400 °C ≤ T ≤ 1000 °C or 650 K ≤ T≤ 1300 K Do not allow high heat If no units for T, then range must be 650 − 1000

1 [17]

Q21. (a) (i) CnH2n / CxH2x

1

(ii) Fractional distillation / GLC / gas liquid chromatography / fractionation Do not allow cracking / distillation

1

(b) (i) But-1-ene / but1ene Ignore hyphens and commas Do not allow butene-1 / but-2-ene / butane / butane /alkene / C4H8 / propene / straight-chain alkene

1

(ii) A structure of cyclobutane or methyl-cyclopropane

Allow skeletal formula. 1

(c) (i) C15H32 → 2C4H8 + C7H16

Do not accept multiples. 1

(ii) Thermal cracking Not catalytic cracking or cracking.

1

To produce products that are in greater demand / more valuable / more expensive / more profitable

The (unsaturated) alkene or the (unsaturated) molecule or X produced can be polymerised or can be made into plastics. Ignore more useful products.

1

(iii) Break (C–C or C–H) bonds Allow to overcome the activation energy. Allow to break the carbon chain.

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Penalise breaking wrong bonds. 1

(d) (i) H2

Only. 1

(ii) Fuel / LPG Allow camping gas, lighter fuel, propellant, refrigerant, cordless appliances. Do not allow petrol or motor fuel. Ignore natural gas.

1

(iii) C4H10 + 2.5O2 → 4C + 5H2O Accept multiples.

1

(iv) SO2 / sulfur dioxide If other sulfur oxides, mark on.

1

Calcium oxide / CaO / lime / quicklime Allow CaCO3 / allow Ca(OH)2 or names. Allow any solid base. M2 dependent on M1. Do not allow limewater.

1

(v) Neutralisation Allow acid-base reaction. Allow flue gas desulfurisation / FGD

1

(e) (Molecules) are similar sizes / have similar Mr / have similar number of electrons Chemical error CE = 0/2 if breaking bonds. Allow similar number of carbon and hydrogen atoms / similar surface area / similar chain length. Can accept same number of carbon atoms. Do not accept same number of H atoms / same number of bonds. Ignore similar amount of bonds.

1

Similar van der Waals forces between molecules / similar intermolecular forces (IMF)

Not similar incorrect IMF eg dipole-dipole 1

[16]

Q22. (a) (i) Crude oil / oil / petroleum

Do not allow ‘petrol’

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1

(ii) Fractional distillation / fractionation / fractionating Not distillation alone

1

(b) (i) 5 Allow five / V

1

(ii) Chain (isomerism) Allow branched chain / chain branched / side chain (isomerism) Ignore position (isomerism) Do not allow straight chain / geometric / branched / function

1

(c) (i) C12H26 / H26C12

Only 1

(ii) Thermal cracking If not thermal cracking, CE = 0/2 If blank mark on

1

High temperature Allow ‘high heat’ for ‘high temperature’

(400°C < T < 900°C) or (650 K < T < 1200 K) Not ‘heat’ alone If no T, units must be 650 – 900

and

High pressure (> 10 atm, > 1 MPa, >1000 kPa) 1

(iii) To produce substances which are (more) in demand / produce products with a high value / products worth more

Ignore ‘to make more useful substances’ 1

(d) (i) Corrosive or diagram to show this hazard symbol Ignore irritant, acidic, toxic, harmful

1

(ii) ( 120.5 × 100) (86 + 71 )

=76.75(%) or 76.8(%) Allow answers > 3 sig figs

1

(e) 2,2-dichloro-3–methylpentane Ignore punctuation

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Any order 1

C3H6Cl 1

[12]

Q23. (a) CH4 + 2O2 → CO2 + 2H2O

Accept multiples Ignore state symbols even if incorrect

1

Not enough oxygen / air 1

CMM / methane is a greenhouse gas / contributes to global warming

Do not allow formation of CO2 / CO2 is a greenhouse gas Apply list principle, eg CH4 is a greenhouse gas and toxic = 0 CH4 is a greenhouse gas and damages ozone = 0 Allow CH4 and CO2 are greenhouses gases Allow collect to use as a fuel so fossil fuels do not run out (as quickly)

1

(b) CH3SH + 3O2 → CO2 + 2H2O + SO2

Accept multiples Ignore state symbols even if incorrect

1

Calcium oxide is basic (and SO2 is acidic) /

CaO neutralises SO2 /

CaO reacts with SO2 to form gypsum / salt / solid / CaSO4 / CaSO3

Allow CaO + SO2 → CaSO3

M2 and M3 can only be scored if SO2 seen somewhere in the answer

1

Acid rain Allow consequence of acid rain eg increased rusting of iron / fish in lakes die / problems for asthmatics Apply list principle Ignore air pollution

1 [6]

Q24.

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(a) (i) C8H18 + 8 O2 → 8CO + 9H2O Accept multiples

1

(ii) Not enough oxygen or air (available for complete combustion) / lack of oxygen or air / too much octane

Ignore poor ventilation, low temp, poor mixing, incomplete combustion

1

(b) (i) 2CO + 2NO → 2CO2 + N2

Allow multiples 1

(ii) Pt / Pd / Rh / Ir or names Apply list principle

1

Big(ger) surface area / increased reaction rate / removes more of the gases / ensures complete reaction

Allow (ceramic) withstands high temperatures 1

(c) (i) Acid rain Allow consequence of acid rain Ignore greenhouse gas / global warming / ozone

1

(ii) CaO/ lime / CaCO3 /limestone Allow chemical names

1

Neutralises the gas or words to that effect/it is basic/ SO2 is acidic Allow ‘reacts with it’ or ‘it is alkaline’ Ignore ‘absorb’

1 [8]

Q25. (a) Cn H2n+2

Allow x in place of n 1

(b)

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Chain Must show every bond Allow branched chain

2

(c) C9H20

Only 1

To break the (C-C and/or C-H) bonds M2=0 if break C=C

1

To make products which are in greater demand / higher value / make alkenes

Not more useful products Allow specific answers relating to question

1

(d) C5H12 + 3O2 → 5C + 6H2O Allow other balanced equations which give C and CO/CO2

1

Causes global dimming / exacerbates asthma / causes breathing problems / makes visibility poor / smog

Apply list principle Ignore causes cancer / toxic

1

(e) (x 100) 1

74.48% Allow 74.5%

1

3 Only

1

(f) 2,3-dichloro-3-methylpentane Ignore punctuation

1

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C3H6Cl Only

1 [13]

Q26. (a) (i) CH4 + 3F2 → CHF3 + 3HF

1

(ii) M1 Initiation

F2 → 2F•

M2 First propagation

F• + CHF3 → •CF3 + HF

M3 Second propagation

F2 + •CF3 → CF4 + F•

M4 Termination (must make C2F6)

2•CF3 → C2F6 or CF3CF3

Penalise absence of dot once only. Radical dot on •CF3 can be anywhere but if the structure is drawn out, the dot must be on the carbon atom. Penalise this error once only. Penalise once only for a line and two dots to show a bond. Penalise each of “Fl” and lower case F, once only in this clip

4

(b) (i) Displayed formula

e.g.

All bonds must be drawn out. Ignore bond angles. Penalise “sticks”

1

(ii) M1 C–Cl bond OR carbon-chlorine bond

M2 chlorine atom OR chlorine (free) radical

M3 2O3 → 3O2

M1 NOT carbon-halogen

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Penalise incorrect spelling of chlorine once only in this clip M2 ignore formulae Ignore Cl2 or Cl• or ClO• balanced on both sides of the equation Ignore other equations leading to the overall equation

3 [9]

Q27. (a) O = 74.1%

1

If atomic numbers or molecular masses are used lose M2

1

1.85 4.63 1 2.5 N2O5

1

This ratio alone will not score the final mark. (It would get 2) Allow 3 marks for N2O5

(b) Toxic/poisonous/forms an acidic gas/forms NO2 which is acidic/ respiratory irritant/forms HNO3 when NO reacts with water and oxygen/ triggers asthma attacks/greenhouse gas/photochemical smog/ contributes to global warming/formation of acid rain

ignore NO is an acidic gas or NO is acidic in water Not references to ozone layer

1

(c) 2NO + O2 → 2NO2

Accept multiples or fractions of equation Ignore wrong state symbols

1

(d) Nitrogen/N2 and oxygen/O2 combine/react QWC (not N and O combine) Not nitrogen in fuel Allow N2 + O2 → 2NO for M1 only

1

spark/high temperature/2500-4000 °C 1

(e) 2NO + 2CO → N2 + 2CO2

OR

2NO → N2 + O2

Accept multiples or fractions of equation Ignore wrong state symbols Allow C8H18 + 25NO → 8CO2 + 12.5N2 + 9H2O

1

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[8]

Q28.

(a) (i) C4H10 + 6 O2 → 4CO2 + 5H2O Allow multiples

1

(ii) insufficient oxygen/low temperature/poor mixing of butane and air

Allow insufficient air Allow lack or oxygen/air Do not allow no oxygen Not incomplete combustion

1

(b) (i) Sulfur dioxide/SO2

Allow sulfur trioxide/SO3

(allow spelling of sulphur to be sulphur) 1

(ii) It is basic/the gas (SO2) is acidic Idea of neutralisation It = calcium oxide

1

(iii) bigger surface area to react Do not allow cheaper

1 [5]

Q29. (a) (Different) boiling points

Ignore mp’s, references to imf, different volatilities 1

(b) (i) Compound which have the same molecular formula Accept same no and type of atom for M1 But If same (chemical) formula M1 = 0 but allow M2 If empirical formula CE = 0/2

1

but different structures/different structural formulae/different displayed formulae

M2 dependent on M1 1

(ii) 3-methylbut-1-ene only ignore commas and hyphens

1

(iii)

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Allow any correct structure with a cyclic alkane

1

Do not allow

i.e with an H missing on one C

(c) C13H28

only 1

Making plastics/used to make polymers or polythene/used to make antifreeze/make ethanol/ripening fruit/any named additional polymer

not used as a plastic/polymer/antifreeze not just ‘polymers’ – we need to see that they are being made

1 [6]

Q30. (a) (i) single (C-C) bonds only/no double (C=C) bonds

1

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Allow all carbon atoms bonded to four other atoms Single C-H bonds only = 0 C=H CE

C and H (atoms) only/purely/solely/entirely Not consists or comprises Not completely filled with hydrogen CH molecules = CE Element containing C and H = CE

1

(ii) CnH2n+2

Formula only CxH2x+2

1

(b) (i) C5H12 + 8O2 → 5CO2 + 6H2O Accept multiples Ignore state symbols

1

(ii) gases produced are greenhouse gases/contribute to Global warming/effect of global warming/climate change

Allow CO2 or water is greenhouse gas/causes global warming Acid rain/ozone CE = 0

1

(c) carbon Allow C Allow soot

1

(d) (i) C9H20 → C5H12 + C4H8

OR

C9H20 → C5H12 + 2C2H4

Accept multiples 1

(ii) Plastics, polymers Accept any polyalkene/haloalkanes/alcohols

1

(iii) so the bonds break OR because the bonds are strong IMF mentioned = 0

1

(e) (i) 1,4-dibromo-1-chloropentane/1-chloro-1,4-dibromopentane Ignore punctuation

1

(ii) Chain/position/positional Not structural or branched alone

1 [11]

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Q31. (a) Single bonds only /no double or multiple bonds;

1

Contains carbon and hydrogen only; C and H only not C and H molecules

1

Alkanes; 1

(b) (1) Fractions or hydrocarbons or compounds have different boiling points/ separation depends on bp;

Ignore mp and vdw 1

(2) bp depends on size/ Mr/ chain length; If refer to bond breaking/cracking/ blast furnace/oxygen/air 2 max

1

(3) Temp gradient in tower or column / cooler at top of column or vice versa;

QWC 1

(4) Higher bp / larger or heavier molecules at bottom (of column) or vice versa;

Not increasing size of fraction Not gases at top

1

(c) Large molecules or compounds or long chain hydrocarbons (broken) into smaller molecules or compounds or smaller chain hydrocarbons;

QWC 1

Zeolite or aluminosilicate (catalyst); 1

C14H30 → C8H18 + C6H12; Only

1

Smaller chain molecules are in more demand or have higher value or vice versa;

Insufficient to say more useful/have more uses 1

(d) C8H18 + 8½ O2 → 8CO + 9H2O; Allow multiples

1

Rh/ Pd/Pt/lr or in words; Penalise contradiction of name and symbol

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1

2CO + 2NO → 2CO2 + N2 / 2CO + O2 → 2CO2; Allow multiples

1

Greenhouse gas/ absorbs infrared radiation; 1

(e) car less powerful/ car stops/ reduced performance/ won’t run smoothly/ can’t accelerate;

Not incomplete combustion or bad effect on engine Not doesn’t go as far.

1

Test it (before sale) /Quality control etc; 1

(f) (compounds with) same molecular formula / same no and type of atoms; Not atoms/elements with same molecular formula. If same chemical formula, can allow M2

1

And different structure/ structural formula; M2 consequential on M1 Allow displayed formula for M2

1

2,2,4-trimethylpentane; Only (but allow numbers in any order)

1 [20]

Q32. (a) (i) Prevents release of toxic CO

More energy efficient (releases more energy on combustion) 1

(ii) C6H14 + 6.5O2 → 6CO + 7H2O 1

Suitable product eg CO or C 1

Balanced equation 1

(iii) Detect CO gas or C (soot or particles) in exhaust gases 1

(b) CH3CH2CH2CH(CH3)2 1

2-methylpentane 1

CH3CH2CH(CH3)CH2CH3 etc 1

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(c) (i) CH3CH2CH2CH=CH2 1

(ii) Alumino silicate etc 1

(iii) Can be made into polymers (or alcohols etc) 1

(d) (i) % atom economy = mass CH2Cl2/total mass reactants = 85 × 100/158

1

= 53.8% 1

(ii) Because expensive chlorine is not incorperated into desired product Raise money by selling HCl

1 [14]

Q33. (a) (i) any two from:

show a gradation/trend/gradual change in physical properties/ a specified property differ by CH2

chemically similar or react in the same way have the same functional group

(penalise ‘same molecular formula’) (penalise ‘same empirical formula’)

2

(ii) fractional distillation or fractionation 1

(iii) contains only single bonds or has no double bonds (credit ‘every carbon is bonded to four other atoms’ provided it does not contradict by suggesting that this will always be H)

1

(b) (i) the molecular formula gives the actual number of atoms of each element/type in a molecule/hydrocarbon/compound/formula

(penalise ‘amount of atoms’) (penalise ‘ratio of atoms’)

1

(ii) C14H30 only (penalise as a contradiction if correct answer is accompanied by other structural formulae)

1

(iii) C10H22 + 5½O2 → 10C + 11H2O (or double this equation)

1

(c) (i) ½N2 + ½O2 → NO

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(or double this equation) 1

(ii) Platinum or palladium or rhodium 1

(iii) 2CO + 2NO → 2CO2 + N2 or

2NO → N2 + O2 or (ignore extra O2 molecules provided the equation balances)

C + 2NO → CO2 + N2

(or half of each of these equations)

C8H18 + 25NO → 8CO2 + 12½N2 + 9H2O (or double this equation)

1 [10]

Q34. M1: uv light/sunlight

OR

T = 450 °C to 1000 °C; (do not credit “high temperature”) (ignore references to pressure or catalyst) (penalise M1 if aqueous chlorine OR chlorine water) (credit M1 if the condition appears over the arrow of the initiation step)

1

M2: Cl2 → 2Cl.; (credit correct half arrows, but penalise (once in the question) the use of double headed arrows)

1

M3: C2H6 + Cl. → CH3CH2. + HCl; (credit CH3CH3 for ethane and C2H5- for the ethyl radical)

1

M4: CH3CH2. + Cl2 → C2H5Cl + Cl.; 1

M5: CH3CH2. + CH3CH2. → C4H10; (penalise the absence of dots once only in this question) (penalise subsequent ionic reactions as contradictions for each reaction contradicted)

(if neither M3 nor M4 scored, allow CH3CH2. + Cl. → C2H5Cl for one mark)

1 [5]

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Q35. (a) (i) (free–) radical substitution

(both words required for the mark) 1

initiation Cl2 → 2Cl· (credit correct half arrows, but penalise double headed arrows)

1

first propagation CH3Cl + Cl· → ·CH2Cl + HCl 1

second propagation ·CH2Cl + Cl2 → CH2Cl2 + Cl (penalise the absence of dots on radicals once only) (penalise radical dot on Cl of CH2Cl once only)

1

(ii) CH3Cl + Cl2 → CH2Cl2 + HCl (penalise if any radicals appear in this equation)

1

(b) M1: mol C = 10.1/12.0 and mol Cl = 89.9/35.5 1

M2: Ratio 0.842 : 2.53 OR 1: 3 OR CCl3 1

M3: 237.0/Mr of CCl3 = 237.0/118.5 = 2 Therefore C2Cl6

(correct answer gains full credit) 1

OR

M1: 237.0 × 10.1/100 and 237 × 89.9/100 1

M2: Ratio 23.9/12.0 : 213/35.5 OR 2 : 6 1

M3: C2Cl6

(correct answer gains full credit) 1

(c) any two from CHBr3 or CBr4 or C2H2Br4 (or CHBr2CHBr2) or C2Br6 (or CBr3CBr3)

(ignore HBr or H2) (ignore equations and ignore names when given in addition to formulae) (penalise names alone)

2 [10]

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Alkenes exam pack

Name: ________________________

Class: ________________________

Date: ________________________

Time: 320 minutes

Marks: 303 marks

Comments:

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Q1. Concentrated sulfuric acid reacts with alkenes, alcohols and sodium halides.

(a) Name the mechanism for the reaction of concentrated sulfuric acid with an alkene.

___________________________________________________________________ (1)

(b) Outline the mechanism for the reaction of concentrated sulfuric acid with propene to show the formation of the major product.

(4)

(c) Draw the structure of the minor product of the reaction between concentrated sulfuric acid and propene.

(1)

(d) Explain why the product shown in your answer to part (b) is the major product.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(e) Butan-2-ol reacts with concentrated sulfuric acid to form a mixture of three isomeric alkenes. Two of the alkenes are stereoisomers.

Draw the skeletal formula of each of the three isomeric alkenes formed by the reaction of butan-2-ol with concentrated sulfuric acid.

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Give the full IUPAC name of each isomer.

Skeletal formula Name

(3)

(f) A by-product of the reaction of butan-2-ol with concentrated sulfuric acid has the molecular formula C4H8O

Name this by-product, identify the role of the sulfuric acid in its formation and suggest the name of a method that could be used to separate the products of this reaction.

By-product __________________________________________________________

___________________________________________________________________

Role of sulfuric acid ___________________________________________________

___________________________________________________________________

Name of separation method

___________________________________________________________________ (3)

(g) Concentrated sulfuric acid reacts with solid sodium chloride.

Give the observation you would make in this reaction.

State the role of the sulfuric acid.

Observation with sodium chloride ________________________________________

___________________________________________________________________

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Role of sulfuric acid ___________________________________________________

___________________________________________________________________ (2)

(h) Concentrated sulfuric acid reacts with solid sodium iodide, to produce several products.

Observations made during this reaction include the formation of a black solid, a yellow solid and a gas with the smell of bad eggs.

Identify the product responsible for each observation.

Black solid _________________________________________________________

Yellow solid _________________________________________________________

Gas _______________________________________________________________ (3)

(Total 19 marks)

Q2. This structure shows a section of a polymer chain formed from the random polymerisation of two different monomers.

Which pair of monomers could produce this polymer?

A CH2=CHF and CH2=CHCF3

B CH2=CH2 and CHF=CHCF3

C CH2=CH2 and CH2=CHCF3

D CH2=CHF and CHCF3=CHF (Total 1 mark)

Q3. 2-Methyl but-2-ene reacts with concentrated sulfuric acid to form two different products.

(a) Outline a mechanism for this reaction to show the formation of the major product.

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(4)

(b) Draw the structure of the minor product of this reaction.

(1)

(c) Explain why the two products are formed in different amounts.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 7 marks)

Q4. What is the empirical formula of 4-hydroxypent-2-ene?

A C5H12O

B C5H10O

C CH2O

D C5H9OH (Total 1 mark)

Q5. Z-Retinal, shown in the diagram, is a component in vitamin A.

Which of the double bonds, labelled A, B, C or D, is responsible for the letter Z in the name?

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A

B

C

D (Total 1 mark)

Q6. This question is about halogenoalkanes.

(a) Chlorine atoms are formed in the upper atmosphere when ultraviolet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break.

Write two equations to show how chlorine atoms catalyse the decomposition of ozone.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

___________________________________________________________________ (2)

(b) Chloroethane reacts with potassium hydroxide in the presence of propan-1-ol to form ethene.

State the role of potassium hydroxide and the role of propan-1-ol in the reaction.

Role of potassium hydroxide ___________________________________________

Role of propan-1-ol ___________________________________________________ (2)

(c) Name and outline a mechanism for the reaction in part (b) between chloroethane and potassium hydroxide to produce ethene.

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Name of mechanism __________________________________________________

Mechanism

(4)

(d) The structure of polymer A is shown.

Draw the structure of the monomer used to form polymer A. (1)

(e) Chemical analysis shows that a chlorofluoroalkane, B, contains by mass 51.6% fluorine, 32.1% chlorine and no hydrogen.

Chlorine exists as two isotopes, 35Cl and 337Cl, in the ratio 3:1 Fluorine only exists as one isotope, 19F.

A mass spectrum of B is obtained using electron impact ionisation. The mass spectrum shows three molecular ion peaks at m/z = 220, 222 and 224.

Determine the formula of each of the three molecular ions of B.

Predict and explain the ratio of the relative abundancies of each of the three molecular ion peaks at m/z = 220, 222 and 224.

To gain full marks you must show all your working. (6)

(Total 15 marks)


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Name _____________________________________________________________


(2)


___________________________________________________________________ (1)

(c) Name polymer Y.

___________________________________________________________________ (1)



___________________________________________________________________ (1)



___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(Total 11 marks)

Q8. A student carried out an experiment to determine the number of C=C double bonds in a molecule of a cooking oil by measuring the volume of bromine water decolourised.

The student followed these instructions:

• Use a dropping pipette to add 5 drops of oil to 5.0 cm3 of inert organic solvent in a conical flask.

• Use a funnel to fill a burette with bromine water. • Add bromine water from a burette to the solution in the conical flask and swirl the

flask after each addition to measure the volume of bromine water that is decolourised.

The student’s results are shown in the table below.

Experiment Volume of bromine water / cm3

1 39.40

2 43.50

3 41.20

(a) In a trial experiment, the student failed to fill the burette correctly so that the gap between the tap and the tip of the burette still contained air.

Suggest what effect this would have on the measured volume of bromine water in this trial. Explain your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________ (2)

(b) Other than incorrect use of the burette, suggest a reason for the inconsistency in the student’s results.

___________________________________________________________________ (1)

(c) Outline how the student could improve this practical procedure to determine the number of C=C double bonds in a molecule of the oil so that more consistent results are obtained.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(d) The oil has a density of 0.92 g cm–3 and each of the 5 drops of oil has a volume of 5.0 × 10–2 cm3. The approximate Mr of the oil is 885. The concentration of bromine water used was 2.0 × 10–2 mol dm–3.

Use these data and the results from experiment 1 to deduce the number of C=C double bonds in a molecule of the oil. Show your working.

(5)

(Total 12 marks)

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Q9. Which statement about ethene is correct?

A It has no geometric isomers because there is free rotation around the C=C bond.

B It reacts with HBr in a nucleophilic addition reaction.

C It burns in excess oxygen to produce carbon dioxide and water.

D The C=C bond is twice as strong as the C–C bond in ethane.

(Total 1 mark)

Q10. Repeating units of two polymers, P and Q, are shown in the figure below.

(a) Draw the structure of the monomer used to form polymer P. Name the type of polymerisation involved.

Monomer

Type of polymerisation ___________________________________________________________________

(2)

(b) Draw the structures of two compounds that react together to form polymer Q.

Structure of compound 1

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Structure of compound 2

(2)

(c) Suggest an environmental advantage of polymer Q over polymer P. Justify your answer.

Advantage __________________________________________________________

Justification _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 7 marks)

Q11. But-1-ene reacts with a reagent of the form HY to form a saturated compound.

(a) Suggest a reagent of the form HY which reacts with but-1-ene.

___________________________________________________________________ (1)

(b) Name and draw a mechanism for the reaction in part (a).


Mechanism

(5)

(c) Explain how three isomeric products are formed when HY reacts with but-1-ene.

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 9 marks)

Q12. What is the major product of the reaction between but-1-ene and DBr? (D is deuterium and represents 2H)

A CH2DCH2CH2CH2Br

B CH2DCH2CHBrCH3

C CH3CH2CHBrCH2D

C CH3CH2CHDCH2Br (Total 1 mark)

Q13. The repeating unit of a polymer is

Which of the following molecules would form a polymer containing this repeating unit?

A But-1-ene

B E-but-2-ene

C Z-but-2-ene

D Methylpropene (Total 1 mark)

Q14.

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The alkene 3-methylpent-2-ene (CH3CH=C(CH3)CH2CH3) reacts with hydrogen bromide to form a mixture of 3-bromo-3-methylpentane and 2-bromo-3-methylpentane.

(a) The alkene 3-methylpent-2-ene (CH3CH=C(CH3)CH2CH3) exists as E and Z stereoisomers.

Draw the structure of Z-3-methylpent-2-ene.

(1)

(b) Name and outline the mechanism for the formation of 3-bromo-3-methylpentane from this reaction of 3-methylpent-2-ene with hydrogen bromide.

Explain why more 3-bromo-3-methylpentane is formed in this reaction than 2-bromo-3-methylpentane.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (7)

(Total 8 marks)

Q15. Compound X (ClCH2COCl) is used as a reagent in organic synthesis.

(a) One important reaction of X is in the preparation of compound P as shown.

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(i) Draw the structure of the electrophile formed by the reaction of X with AlCl3.

(1)

(ii) Outline the mechanism for the reaction of the electrophile from part (a)(i) with benzene in the preparation of P.

(3)

(b) Compound Q is an alternative product that could be formed when X reacts with benzene.

Describe how you could distinguish between P and Q by a test-tube reaction. Give the reagent used and the observation with each compound.

Reagent _________________________________________________________

Observation with P _________________________________________________

Observation with Q _________________________________________________ (3)

(c) X is also used to make the compound HOCH2COOH. This compound is polymerised to form the polymer known as PGA. PGA is used in surgical sutures (stitches).

(i) Draw the repeating unit of PGA.

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(1)

(ii) Production of PGA occurs via a cyclic compound. Two HOCH2COOH molecules react together to form the cyclic compound and two molecules of water.

Draw the structure of this cyclic compound.

(1)

(d) Poly(propene) is also used in surgical sutures.

(i) Draw the repeating unit of poly(propene).

(1)

(ii) Suggest an advantage of surgical sutures made from PGA rather than from poly(propene). Explain your answer.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(Total 12 marks)

Q16. Consider the following scheme of reactions.

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(a) Give the IUPAC name for compound P and that for compound Q.

P _________________________________________________________________

Q _________________________________________________________________ (2)

(b) The conversion of P into Q in Reaction 1 uses HCl

Name and outline a mechanism for this reaction.

___________________________________________________________________ (5)

(c) The conversion of Q into R in Reaction 2 uses NH3

Name and outline a mechanism for this reaction.

___________________________________________________________________ (5)

(d) State the type of reaction shown by Reaction 3.

Identify a reagent for this reaction.

Give one condition necessary for a high yield of product when Q is converted into P.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

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(e) Hydrogen bromide (HBr) could be used in the overall conversion of P into R, instead of using HCl Hydrogen bromide is made by the reaction of NaBr with concentrated phosphoric acid. Concentrated sulfuric acid is not used to make HBr from NaBr

Write an equation for the reaction of NaBr with H3PO4 to produce HBr and Na3PO4 only.

Identify two toxic gases that are formed, together with HBr, when NaBr reacts with concentrated H2SO4

State the role of H2SO4 in the formation of these two toxic gases.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 19 marks)

Q17. The following table gives the names and structures of some structural isomers with the molecular formula C5H10.

Name of isomer Structure

Isomer 1 pent-2-ene CH3CH = CHCH2CH3

Isomer 2 cyclopentane

Isomer 3 3-methylbut-1-ene (CH3)2CHCH = CH2

Isomer 4 2-methylbut-2-ene (CH3)2C = CHCH3

Isomer 5 2-methylbut-1-ene H2C = C(CH3)CH2CH3

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(a) Isomer 1 exists as E and Z stereoisomers.

(i) State the meaning of the term stereoisomers.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) Draw the structure of the E stereoisomer of Isomer 1.

(1)

(b) A chemical test can be used to distinguish between separate samples of Isomer 1 and Isomer 2.

Identify a suitable reagent for the test. State what you would observe with Isomer 1 and with Isomer 2.

Reagent ___________________________________________________________

Observation with Isomer 1 _____________________________________________

___________________________________________________________________

Observation with Isomer 2 _____________________________________________

___________________________________________________________________ (3)

(c) Use Table A on the Data Sheet when answering this question. Isomer 3 and Isomer 4 have similar structures.

(i) State the infrared absorption range that shows that Isomer 3 and Isomer 4 contain the same functional group.

______________________________________________________________

______________________________________________________________ (1)

(ii) State one way that the infrared spectrum of Isomer 3 is different from the infrared spectrum of Isomer 4.

______________________________________________________________

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______________________________________________________________

______________________________________________________________ (1)

(d) Two alcohols are formed by the hydration of Isomer 4.

Draw the displayed formula for the alcohol formed that is oxidised readily by acidified potassium dichromate(VI).

(1)

(e) Isomer 4 reacts with hydrogen bromide to give two structurally isomeric bromoalkanes.

(i) Name and outline a mechanism for the reaction of Isomer 4 with hydrogen bromide to give 2-bromo-2-methylbutane as the major product.

(CH3)2C = CHCH3 + HBr (CH3)2CBrCH2CH3

Name of mechanism ____________________________________________

Mechanism

(5)

(ii) The minor product in this reaction mixture is 2-bromo-3-methylbutane.

Explain why this bromoalkane is formed as a minor product.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(f) Name and outline a mechanism for the following reaction to form Isomer 5. State the role of the hydroxide ion in this reaction.

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(CH3)2CBrCH2CH3 + KOH H2C = C(CH3)CH2CH3 + KBr + H2O


Mechanism

Role of hydroxide ion _________________________________________________ (5)

(Total 21 marks)

Q18. Sulfuric acid is manufactured by the Contact Process.

(a) In this process, sulfur dioxide reacts with oxygen. The equation for the equilibrium that is established is

SO2(g) + O2(g) SO3(g) ΔH = −98 kJ mol−1

(i) State and explain the effect of a decrease in temperature on the equilibrium yield of SO3.

Effect of a decrease in temperature on yield ___________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(ii) Give two features of a reaction at equilibrium.

Feature 1 ______________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

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Feature 2 ______________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(b) Write an equation for the reaction of concentrated sulfuric acid with potassium bromide to form potassium hydrogensulfate and hydrogen bromide.

___________________________________________________________________ (1)

(c) Bromine is one of the products formed when concentrated sulfuric acid reacts with hydrogen bromide.

Write an equation for this reaction. State the role of sulfuric acid in this reaction.

Equation

___________________________________________________________________

Role of sulfuric acid ___________________________________________________ (3)

(d) Concentrated sulfuric acid is used in a two-stage process to convert 2-methylpropene into 2-methylpropan-2-ol.

Stage 1 (CH3)2C=CH2 + H2SO4 (CH3)2C(OSO2OH)CH3

Stage 2 (CH3)2C(OSO2OH)CH3 + H2O (CH3)2C(OH)CH3 + H2SO4

(i) Name and outline a mechanism for Stage 1 of this conversion.

Name of mechanism ____________________________________________

Mechanism

(5)

(ii) Deduce the type of reaction in Stage 2 of this conversion.

______________________________________________________________ (1)

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(iii) State the overall role of sulfuric acid in this conversion.

______________________________________________________________ (1)

(Total 16 marks)

Q19. In each of the following questions, you should draw the structure of the compound in the space provided.

(a) Draw the structure of the alkene that would form 1,2-dibromo-3-methylbutane when reacted with bromine.

(1)

(b) Draw the structure of the alcohol with molecular formula C4H10O that is resistant to oxidation by acidified potassium dichromate(VI).

(1)

(c) Draw the structure of the alkene that has a peak, due to its molecular ion, at m/z = 42 in its mass spectrum.

(1)

(d) Draw the structure of the organic product with Mr = 73, made from the reaction between 2-bromobutane and ammonia.

(1)

(Total 4 marks)

Q20. The alkene (E)-but-2-enenitrile is used to make acrylic plastics. The structure of (E)-but-2-enenitrile is

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(a) (i) Draw the structure of (Z)-but-2-enenitrile.

(1)

(ii) Identify the feature of the double bond in the E and Z isomers that causes them to be stereoisomers.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(b) Draw the repeating unit of the polyalkene formed by addition polymerisation of (E)-but-2-enenitrile.

(1)

(c) Consider the infrared spectrum of (E)-but-2-enenitrile.

Wavenumber / cm−1

Identify two features of the infrared spectrum that support the fact that this is the infrared spectrum for but-2-enenitrile. You may find it helpful to refer to Table 1 on the Data Sheet.

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Feature 1 ___________________________________________________________

___________________________________________________________________

___________________________________________________________________

Feature 2 ___________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 5 marks)

Q21. Consider the following reactions.

(a) Name and outline a mechanism for Reaction 1.

Name of mechanism _________________________________________________

Mechanism

(5)

(b) Name and outline a mechanism for Reaction 2.

Name of mechanism _________________________________________________

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Mechanism

(5)

(c) State the type of reaction in Reaction 3. Give the name of substance X.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) The haloalkane produced in Reaction 1 can be converted back into propene in an elimination reaction using ethanolic potassium hydroxide.

CH3CHBrCH3 H2C=CHCH3

Outline a mechanism for this conversion.

(3)

(Total 15 marks)

Q22. It is possible to convert but-1-ene into its structural isomer but-2-ene.

(a) State the type of structural isomerism shown by but-1-ene and but-2-ene.

___________________________________________________________________

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(1)

(b) The first stage in this conversion involves the reaction of hydrogen bromide with but-1-ene.

CH3CH2CH=CH2 + HBr CH3CH2CHBrCH3

Outline a mechanism for this reaction.

(4)

(c) The second stage is to convert 2-bromobutane into but-2-ene.

CH3CH2CHBrCHCH3 + KOH CH3CH=CHCH3 + KBr + H2O

Outline a mechanism for this reaction.

(3)

(Total 8 marks)

Q23. Items softened with plasticisers have become an essential part of our modern society.

Compound S, shown below, is commonly known as phthalic acid.

Esters of phthalic acid are called phthalates and are used as plasticisers to soften polymers such as PVC, poly(chloroethene).

(a) Give the IUPAC name for phthalic acid.

___________________________________________________________________ (1)

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(b) Draw the displayed formula of the repeating unit of poly(chloroethene).

(1)

(c) The ester diethyl phthalate (DEP) is used in food packaging and in cosmetics.

(i) Complete the following equation showing the formation of DEP from phthalic anhydride.

(2)

(ii) Deduce the number of peaks in the 13C n.m.r. spectrum of DEP.

______________________________________________________________ (1)

(iii) One of the peaks in the 13C n.m.r. spectrum of DEP is at δ = 62 ppm.

Table 3 on the Data Sheet can be used to identify a type of carbon atom responsible for this peak.

Draw a circle around one carbon atom of this type in the structure below.

(1)

(d) The mass spectrum of DEP includes major peaks at m/z = 222 (the molecular ion) and at m/z = 177

Write an equation to show the fragmentation of the molecular ion to form the fragment that causes the peak at m/z = 177

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___________________________________________________________________ (2)

(e) Because of their many uses, phthalates have been tested for possible adverse effects to humans and to the environment.

An organisation that represents the manufacturers of plasticisers asserts that experimental evidence and research findings show that phthalates do not pose a risk to human health because they biodegrade in a short time scale.

According to the organization’s research, phthalates do not represent a risk for humans or for the environment and they are biodegradable.

(i) Hydrolysis of DEP in an excess of water was found to follow first order kinetics.

Write a rate equation for this hydrolysis reaction using DEP to represent the ester.

______________________________________________________________ (1)

(ii) Suggest what needs to be done so that the public could feel confident that the research discussed above is reliable.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(Total 11 marks)

Q24. Fibres are made from natural and from synthetic polymers. Both types of polymer have advantages and disadvantages.

(a) Amino acids are the building blocks of naturally-occurring polymers called proteins.

Consider the following amino acid.

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(i) Draw the structure of the amino acid species present in a solution at pH 12.

(ii) Use your understanding of amino acid chemistry to deduce the structure of the dipeptide formed from two molecules of this amino acid and illustrate your answer with a sketch showing the structure of the dipeptide.

(iii) Protein chains are often arranged in the shape of a helix. Name the type of interaction that is responsible for holding the protein chain in this shape.

______________________________________________________________ (3)

(b) Alkenes are the building blocks of synthetic addition polymers.

Consider the hydrocarbon G, (CH3)2C=CHCH3, which can be polymerised.

(i) Draw the repeating unit of the polymer.

(ii) Draw the structure of an isomer of G which shows E-Z isomerism.

(iii) Draw the structure of an isomer of G which does not react with bromine water.

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(3)

(c) Draw the repeating unit of the polymer formed by the reaction between butanedioic acid and hexane-1,6-diamine.

(2)

(d) Two plastic objects were manufactured, one from the polyalkene represented by the repeating unit in part (b)(i) and the other from the polyamide represented by the repeating unit in part (c).

After use it was suggested that both objects be disposed of as landfill.

(i) Describe an experiment in which you could compare the biodegradability of these two objects.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Describe an advantage or a disadvantage of a different method of disposal of such objects compared with landfill.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(Total 14 marks)

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Q25. Which one of the following is not a correct statement about vitamin C, shown below?

A It is a cyclic ester.

B It can form a carboxylic acid on oxidation.

C It decolourises a solution of bromine in water.

D It is a planar molecule. (Total 1 mark)

Q26. Which one of the following reactions will produce an organic compound that has optical isomers?

A dehydration of butan-2-ol by heating with concentrated sulphuric acid

B reduction of pentan-3-one by warming with NaBH4

C addition of Br2 to 3-bromopropene

D reduction of 2,3-dimethylpent-2-ene with H2 in the presence of a nickel catalyst (Total 1 mark)

Q27. Glucose can be used as a source of ethanol. Ethanol can be burned as a fuel or can be converted into ethene.

C6H12O6 → CH3CH2OH → H2C=CH2

glucose ethanol ethene

(a) Name the types of reaction illustrated by the two reactions above.

Glucose to ethanol __________________________________________________

Ethanol to ethene ___________________________________________________ (2)

(b) (i) State what must be added to an aqueous solution of glucose so that ethanol is formed.

______________________________________________________________

(ii) Identify a suitable catalyst for the conversion of ethanol into ethene.

______________________________________________________________ (2)

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(c) (i) State the class of alcohols to which ethanol belongs.

______________________________________________________________

(ii) Give one advantage of using ethanol as a fuel compared with using a petroleum fraction.

______________________________________________________________ (2)

(d) Most of the ethene used by industry is produced when ethane is heated to 900°C in the absence of air. Write an equation for this reaction.

___________________________________________________________________ (1)

(e) Name the type of polymerisation which occurs when ethene is converted into poly(ethene).

___________________________________________________________________ (1)

(Total 8 marks)

Q28. Tetrafluoroethene, C2F4, is obtained from chlorodifluoromethane, CHClF2, according to the equation:

2CHClF2(g) C2F4(g) + 2HCl(g) ΔHο = +128kJ mol–1

(a) A 1.0 mol sample of CHClF2 is placed in a container of volume 18.5 dm3 and heated.

When equilibrium is reached, the mixture contains 0.20 mol of CHClF2

(i) Calculate the number of moles of C2F4 and the number of moles of HCl present at equilibrium.

Number of moles of C2F4 _________________________________________

Number of moles of HCl __________________________________________

(ii) Write an expression for Kc for the equilibrium.

______________________________________________________________

(iii) Calculate a value for Kc and give its units.

Calculation ____________________________________________________

______________________________________________________________

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______________________________________________________________

______________________________________________________________

Units _________________________________________________________ (6)

(b) (i) State how the temperature should be changed at constant pressure to increase the equilibrium yield of C2F4

______________________________________________________________

(ii) State how the total pressure should be changed at constant temperature to increase the equilibrium yield of C2F4

______________________________________________________________ (2)

(c) C2F4 is used to manufacture the polymer polytetrafluoroethene, PTFE. Name the type of polymerisation involved in the formation of PTFE.

___________________________________________________________________ (1)

(Total 9 marks)

Q29. (a) Addition reactions to both alkenes and carbonyl compounds can result in the

formation of isomeric compounds.

(i) Choose an alkene with molecular formula C4H8 which reacts with HBr to form two structural isomers. Give the structures of these two isomers and name the type of structural isomerism shown.

Outline a mechanism for the formation of the major product.

(ii) Using HCN and a suitable carbonyl compound with molecular formula C3H6O, outline a mechanism for an addition reaction in which two isomers are produced. Give the structures of the two isomers formed and state the type of isomerism shown.

(14)

(b) Explain why ethanoyl chloride reacts readily with nucleophiles. Write an equation for one nucleophilic addition–elimination reaction of ethanoyl chloride. (A mechanism is not required.)


Q30. Consider the following reaction scheme.

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(a) (i) Name the mechanism for Reaction 1.

______________________________________________________________

(ii) Explain why 1-bromopropane is only a minor product in Reaction 1.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(b) Give a suitable reagent and state the essential conditions required for Reaction 3.

Reagent ___________________________________________________________

Conditions _________________________________________________________ (2)

(c) The reagent used for Reaction 3 can also be used to convert 2-bromopropane into propene. State the different conditions needed for this reaction.

___________________________________________________________________ (1)

(d) Reaction 2 proceeds in two stages.

Stage 1 CH3CH=CH2 + H2SO4 → CH3CH(OSO2OH)CH3

Stage 2 CH3CH(OSO2OH)CH3 + H2O → CH3CH(OH)CH3 + H2SO4

(i) Name the class of alcohols to which propan-2-ol belongs.

______________________________________________________________

(ii) Outline a mechanism for Stage 1 of Reaction 2, using concentrated sulphuric acid.

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(iii) State the overall role of the sulphuric acid in Reaction 2.

______________________________________________________________ (6)

(Total 12 marks)

Q31. For this question refer to the reaction scheme below.

Which one of the following statements is not correct?

A Reaction of W with sodium cyanide followed by hydrolysis of the resulting product gives propanoic acid.

B Mild oxidation of Z produces a compound that reacts with Tollens’ reagent, forming a silver mirror.

C Z reacts with ethanoic acid to produce the ester propyl ethanoate.

C W undergoes addition polymerisation to form poly(propene). (Total 1 mark)

Q32. For this question refer to the reaction scheme below.

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Which one of the following reagents would not bring about the reaction indicated?

A Step 1 : alcoholic KOH

B Step 2 : aqueous Br2

C Step 3 : aqueous NaOH

C Step 4 : concentrated H2SO4

(Total 1 mark)

Q33. (a) Compounds with double bonds between carbon atoms can exhibit geometrical

isomerism.

(i) Draw structures for the two geometrical isomers of 1,2-dichloroethene.

Isomer 1 Isomer 2

(ii) What feature of the double bond prevents isomer 1 from changing into isomer 2?

______________________________________________________________ (3)

(b) When 2-chloropropane reacts with sodium hydroxide, two different reactions occur. Each reaction produces a different organic product.

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(i) Outline a mechanism for Reaction 1 and state the role of the hydroxide ion in this reaction.

Mechanism

Role of the hydroxide ion __________________________________________

(ii) Outline a mechanism for Reaction 2 and state the role of the hydroxide ion in this reaction.

Mechanism

Role of the hydroxide ion __________________________________________ (7)

(Total 10 marks)

Q34. (a) Propene reacts with hydrogen bromide by an electrophilic addition mechanism

forming 2-bromopropane as the major product.

The equation for this reaction is shown below.

(i) Outline the mechanism for this reaction, showing the structure of the intermediate carbocation formed.

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(ii) Give the structure of the alternative carbocation which could be formed in the reaction between propene and hydrogen bromide.

(5)

(b) A substitution reaction occurs when 2-bromopropane reacts with aqueous sodium hydroxide.

(i) Draw the structure of the organic product of this reaction and give its name.

Structure

Name _________________________________________________________

(ii) Name and outline the mechanism for this reaction.

Name of mechanism _____________________________________________

Mechanism

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(5)

(c) Under different conditions, 2-bromopropane reacts with sodium hydroxide to produce propene.

(i) Name the mechanism for this reaction.

______________________________________________________________

(ii) State the role of sodium hydroxide in this reaction.

______________________________________________________________ (2)

(Total 12 marks)

Q35. The reaction scheme below shows the conversion of compound A, 2-methylbut-1-ene, into compound B and then into compound C.

(a) The structure of A is shown below. Circle those carbon atoms which must lie in the same plane.

(1)

(b) Outline a mechanism for the reaction in Step 1.

(4)

(c) State the reagent and condition used in Step 2. Name compound C.

Reagent ___________________________________________________________

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Condition __________________________________________________________

Name of compound C ________________________________________________ (3)

(d) When compound A is converted into compound C, a second alcohol, D, is also formed. Alcohol D is isomeric with C but is formed as a minor product. Identify alcohol D and explain why it is formed as the minor product.

Identity of alcohol D __________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 11 marks)

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Mark schemes

Q1. (a) electrophilic addition

ALLOW phonetic e.g. electrophylic, electrophillic 1

(b)

M1: must show an arrow from = of C=C towards the H atom of the H–O bond or

HO that is part of H–O–S–… on a compound with molecular formula H2SO4

M1 could have arrow to H+ in which case M2 would be for an independent H–O bond break on a compoundwith formula H2SO4

ALLOW CH3–C+ etc for carbocation No need for hydrogensulfate to be displayed If H2O used as electrophile – max M3 ONLY

M2: must use an arrow to show the breaking of the H–O bond M2 ignore partial charges unless wrong

M3: is for the correct carbocation structure NOT M3 if primary carbocation shown.

M4: must show an arrow from a lone pair of electrons on the correct oxygen of the negatively charged ion towards the positively charged carbon atom

M4 NOT HSO4

credit as shown (or −:OSO2OH) or as :OSO3H – in which case negative charge can be shown anywhere ecf from H2SO3 in M1

NB: The arrows are double-headed IGNORE subsequent use of water to hydrolyse hydrogensulfate

4

(c) minor product = CH3CH2CH2OSO3H ecf from 1° in (b) for CH3CH(OSO3H)CH3

ecf from alcohol as product in (b) ecf from side chain such as –OHSO3 or –HSO4 in (b)

1

(d) (major) product formed via more stable carbocation OR secondary carbocation more stable (than primary)

1

Due to electron-releasing character / (positive) inductive effect of two alkyl / methyl groups (as opposed to one)

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1

ALLOW ‘more’ alkyl groups in place of ‘two’ alkyl groups

(e)

matching name and formula for each mark One ‘salvage’ mark available for 3 correct structures or 3 correct names if no other mark awarded use of trans and cis can score 1/2 for the two but-2-ene structures

3

(f) butanone ALLOW butan-2-one

1

oxidising agent ALLOW electron acceptor but NOT electron pair acceptor

1

(fractional) distillation ALLOW gas chromatography

1

(g) white / misty / steamy fumes NOT gas evolved / effervescence

1

acid/proton donor 1

(h) iodine / I2

IGNORE state symbols 1

sulfur / S / S8

If name and formula given they must both be right 1

hydrogen sulfide / H2S 1

[19]

Q2. A

[1]

Q3. (a)

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M1, M2 and M4 are awarded for the three curly arrows shown on the mechanism (1 mark for each correct)

M3 is for the structure of the carbocation intermediate 4

(b)

Correct answers include: • the displayed formula • structural formulae such as CH3CH(CH3)CH(OSO3H)CH3

• skeletal formulae such as

1

(c) The major product is formed via a tertiary carbocation intermediate and the minor product is formed via a secondary carbocation intermediate

1

The tertiary carbocation is more stable than the secondary carbocation 1

[7]

Q4. B

[1]

Q5. C

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[1]

Q6. (a) Cl• + O3 ⟶ ClO• + O2

Allow dot in free-radical on either O or Cl. 1

ClO• + O3 ⟶ 2O2 + Cl• 1

(b) (KOH acts as a) base 1

(propan-1-ol acts as a) solvent. Allow product of reaction between KOH and propan-1-ol / CH3CH2CH2O− acts as base.

1

(c) (Name of mechanism) Elimination 1

mechanism: 3 arrows (1 mark each).

3

(d)

1


Level 3

All stages are covered & the explanation of each stage is generally correct and virtually complete. Stages 1 and 2 are supported by correct data. Answer communicates the whole process coherently and shows a logical progression from stage 1 to stage 2 and then stage 3.

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Steps in stage 3 are in logical order and working is shown. If there is no working for ratio or statement of ratio then full marks cannot be awarded.

If the formulae of the three molecular ions are not correct (2d) then the student can’t access Level 3 (any incorrect chemistry drops the student to the bottom mark within the level they have achieved).

5-6 marks

Level 2

Stage 2 is attempted (2a-2c do not need to be explicitly stated) but the calculation may contain inaccuracies OR the explanation may be incomplete OR first two stages are covered and the explanations are generally correct and virtually complete. Answer is mainly coherent and shows a progression through the first two stages. Some steps in each stage may be incomplete.

If percentage of carbon is missing or incorrect (1a) then student can’t access Level 2.

3-4 marks

Level 1

Stage 1 needs to be attempted but may contain inaccuracies.

OR

Stage 3 attempted but may contain inaccuracies / molecular formula not determined.

Answer includes some isolated statements, but these are not presented in a logical order or show confused reasoning.

1-2 marks

Level 0

Insufficient correct chemistry to warrant a mark. 0 marks

Indicative Chemistry content Stage 1 (determines empirical formula) 1a 16.3% carbon 1b Divide by Ar

1c Divide by smallest (0.904) 1d Convert ratio in simplest integer (x 2)

C Cl F

= 1.358 = 0.904 = 2.716

3 2 6

Stage 2 (determines formulae of three molecular ions) 2a For E.F. Mr (corresponds to the molecule) = 221

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2b since Mr = 221 lies within molecular ion range 220–224 2c Thus empirical formula = molecular formula 2d Three correct formulae 2e Correct Mr for each of three molecules

220 222 224

Stage 3 (explains the ratio of 3 molecular ion peaks) 3a Working 2b Correct (simplified) ratio 9:6:1 Note: 9:3:1 will be a common incorrect answer (max 5).

Working:

220 222 224

and

[15]

Q7. (a) Alkenes

1


1


1


(d) High pressure Allow pressure � MPa

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Mention of catalyst loses the mark 1


Level 3

All stages are covered and the explanation of each stage is generally correct and virtually complete.


5–6 marks

Level 2



3–4 marks

Level 1



1–2 marks

Level 0


Indicative chemistry content Stage 1: consider effect of higher temperature on yield (Or vice versa for lower temperature) • Le Chatelier’s principle predicts that equilibrium shifts to oppose any increase in temperature • Exothermic reaction, so equilibrium shifts in endothermic direction / to the left • So a Higher T will reduce yield Stage 2: consider effect of higher temperature on rate (Or vice versa for lower temperature) • At higher temperature, more high energy molecules • more collisions have E>Ea • So rate of reaction increases / time to reach equilibrium decreases Stage 3: conclusion Industrial conditions chosen to achieve (cost-effective)

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balance of suitable yield at reasonable rate [11]

Q8. (a) Measured volume would be greater

1

Level in burette falls as tap is filled before any liquid is delivered 1

(b) Drop sizes vary Allow percentage error for amount of oil will be large as the amount used is so small

1

(c) Use a larger single volume of oil 1

Dissolve this oil in the organic solvent 1

Transfer to a conical flask and make up to 250 cm3 with more solvent 1

Titrate (25 cm3) samples from the flask 1

(d) Stage 1

Mass of oil = 0.92 × (5.0 × 10–2 × 5) = 0.23 (g) 1

Mol of oil = 0.23 / 885 = 2.6 × 10–4

1

Extended response calculation To gain 4 or 5 marks, students must show a logical progression from stage 1 and stage 2 (in either order) to stage 3

Stage 2

Mol bromine = 2.0 × 10–2 × 39.4 / 1000 = 7.9 × 10–4

1

Stage 3

Ratio oil : bromine

2.6 × 10–4 : 7.9 × 10–4

Simplest ratio = 2.6 × 10–4 / 2.6 × 10-4 : 7.9 × 10–4 / 2.6 × 10–4

= 1 : 3 1

Hence, 3 C=C bonds M5 cannot be awarded unless working for M4 is shown

1

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[12]

Q9. C

[1]

Q10. (a)

1

Addition 1

(b)

1

1

(c) Q is biodegradable 1

Polar C=O group or δ+ C in Q (but not in P) 1

Therefore, can be attacked by nucleophiles (leading to breakdown) 1

[7]

Q11. (a) HBr OR HCl OR H2SO4

Allow HI or HY 1

(b) Electrophilic addition 1

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Allow consequential marking on acid in 12.1 and allow use of HY

4

(c) The major product exists as a pair of enantiomers 1

The third isomer is 1-bromobutane (minor product) 1

Because it is obtained via primary carbocation 1

[9]

Q12. C

[1]

Q13. D

[1]

Q14.

(a) Must show all 4 groups bonded to C=C Allow CH3− for methyl group; allow C2H5 for ethyl group Allow correct structure of the style

Allow correct skeletal structure

1

(b) M1 electrophilic addition

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NB the arrows here are double-headed 1

M2 must show an arrow from the double bond towards the H atom of the H-Br molecule

1

M3 must show the breaking of the H-Br bond 1

M4 is for the structure of the tertiary carbocation 1

M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged atom (of either a secondary or) of a tertiary carbocation

1

M6 3-bromo-3-methylpentane is formed from 3y carbocation OR 2-bromo-3-methylpentane is formed from 2y carbocation

1

M7 3y carbocation more stable than 2y

1

M2-M5 Penalise one mark from their total if half-headed arrows are used M2 Ignore partial negative charge on the double bond M3 Penalise incorrect partial charges on H-Br bond and penalise formal charges Penalise M4 if there is a bond drawn to the positive charge Penalise only once in any part of the mechanism for a line and two dots to show a bond Max 3 of any 4 marks (M2-5) for wrong organic reactant or wrong organic product (if shown) or secondary carbocation Max 2 of any 4 marks in the mechanism for use of bromine Do not penalise the “correct” use of “sticks” For M5, credit attack on a partially positively charged carbocation structure but penalise M4 M6 is high demand and must refer to product being

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formed from/via correct class of carbocation M7 is high demand and must be clear answer refers to stability of carbocations (intermediates) not products Candidate that states that products are carbocations would lose M6 and M7 M6,7 allow carbonium ion in place of carbocation; or a description of carbocation in terms of alkyl groups/ number of carbon atoms joined to a positive C

When asked to outline a mechanism, candidates are expected to draw a mechanism with curly arrows (specification 3.3.1.2). On this occasion only we would allow a detailed description as shown. M2 must describe the movement of a pair of electrons / curly arrow from the C=C towards the H atom of the H-Br molecule M3 must describe the breaking of the H-Br bond with the bonding pair of electrons moving to the Br / curly arrow from H-Br bond to Br M4 is for the structure of the tertiary carbocation (i.e. positive C bonded to one methyl and two ethyl groups) M5 must describe the movement of a pair of electrons from the Br− ion to the positive C atom of the carbocation / curly arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged C atom (of either a secondary or) of a tertiary carbocation

[8]

Q15.

(a) (i) Allow [ClCH2CO]+

1

(ii) M1 for arrow from inside hexagon to C or + on C on correct electrophile M2 for structure of intermediate • Horseshoe centred on C1; • + in intermediate not too close to C1 (allow on or “below” a line from C2 to C6) M3 for Arrow from bond to H into ring • Allow M3 arrow independent of M2 structure • + on H in intermediate loses M2 not M3 • Ignore Cl- removing H+

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1 1 1

(b) Reagent

Water

(Aqueous) silver nitrate

NaOH followed by acidified silver nitrate

(Water +) named indicator Named alcohol Na2CO3 or NaHCO3

Ammonia 1

P

No reaction

No reaction (or slow formation of ppt)

No reaction (or slow formation of ppt)

No colour change NVC NVC No reaction Do NOT award No observation

1

Q

Steamy /misty/ white fumes

White precipitate (immediately formed)

White precipitate (immediately formed)

Indicator turns to correct acid colour Fruity or sweet smell or misty fumes Fizzing or effervescence (not just gas produced) White smoke

1

(c) (i)

One unit only Must have trailing bonds

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Ignore n and brackets

allow 1

(i) Allow CO for C=O

1

(d) (i) One unit only Must have trailing bonds Ignore n and brackets

1

(ii) PGA sutures react/dissolve/break down/are biodegradable/ are hydrolysed / attacked by water or nucleophiles /no need to remove

OR Polypropene not biodegradeable/ not hydrolysed / not attacked by water/nucleophiles

1

(Ester links have) polar bonds polypropene contains non-polar bonds ignore intermolecular forces

1 [12]

Q16. (a) P 3,3−dimethylbut−1−ene

OR accept 3,3−dimethylbutene

Ignore absence of commas, hyphens and gaps Require correct spelling

Q 3−chloro−2,2−dimethylbutane OR

accept 2−chloro−3,3−dimethylbutane In Q, “chloro” must come before “dimethyl”

2

(b) M1 Electrophilic addition

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M2 must show an arrow from the double bond towards the H atom of HCl M3 must show the breaking of the H−Cl bond M4 is for the structure of the carbocation M5 must show an arrow from the lone pair of electrons on the negatively charged chloride ion towards the positively charged carbon atom on their carbocation.

NB The arrows here are double−headed M1 both words required For the mechanism M3 Penalise incorrect partial charge on H−Cl bond and penalise formal charges Ignore partial negative charge on the double bond. Maximum 3 of 4 marks for a correct mechanism using HBr or the wrong organic reactant or wrong organic product (if shown) or a primary carbocation Penalise once only in any part of the mechanism for a line and two dots to show a bond Credit the correct use of “sticks” For M5, credit attack on a partially positively charged carbocation structure, but penalise M4

5

(c) M1 Nucleophilic substitution For M1, both words required. Accept phonetic spelling

M2 must show an arrow from the lone pair of electrons on the nitrogen atom of an ammonia molecule to the correct C atom M3 must show the movement of a pair of electrons from the C− Cl bond to the Cl atom. Mark M3 independently provided it is from their original molecule M4 is for the structure of the alkylammonium ion, which could be a condensed formula. A positive charge must be shown on, or close to, the N atom. M5 is for an arrow from the N−H bond to the N atom Award full marks for an SN1 mechanism in which M2 is the attack of the ammonia on the intermediate carbocation

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NB These are double-headed arrows For the mechanism Penalise M2 if NH3 is negatively charged. Penalise M3 for formal charge on C of the C−Cl or incorrect partial charges on C−Cl Penalise M3 for an additional arrow from the Cl to something else The second mole of ammonia is not essential for M5; therefore ignore any species here Penalise once only for a line and two dots to show a bond Maximum 3 of 4 marks for the mechanism for wrong organic reactant OR wrong organic product if shown Accept the correct use of “sticks”

5

(d) M1 (base) elimination M1 Dehydrohalogenation

M2 KOH OR NaOH M3 Must be consequential on a correct reagent in M2, but if incomplete or inaccurate attempt at reagent (e.g. hydroxide ion), penalise M2 only and mark on

Any one from • high temperature OR hot OR heat / boil under reflux • concentrated • alcohol / ethanol (as a solvent) / (ethanolic conditions)

M3 not “reflux” alone M3 if a temperature is stated it must be in the range 78C to 200 °C Ignore “pressure”

3

(e) M1 3NaBr + H3PO4 3HBr + Na3PO4

M1 Credit correct ionic species in the equation

M2 and M3 SO2 and Br2 identified M4 Concentrated sulfuric acid • is an oxidising agent • oxidises the bromide (ion) or Br− or NaBr or HBr • is an electron acceptor

In M2 and M3 the two gases need to be identified. If equations are used using sulfuric acid and the toxic gases are not identified clearly, allow one mark for the formulas of SO2 and Br2

• apply the list principle as appropriate but ignore any reference to HBr • the marks are for identifying the two gases either by name or formula

4 [19]

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Q17. (a) (i) M1 (Compounds / molecules with) the same structural formula

Penalise M1 if ‘same structure’ or ‘different structural / displayed formula’.

M2 with atoms / bonds / groups arranged differently in space

OR atoms / bonds / groups with different spatial arrangements / different orientation

Ignore references to ‘same molecular formula’ or ‘same empirical formula’. Mark independently.

2

(ii)

Credit C–H3C Credit C2H5

Penalise C–CH3CH2 1

(b) M1 Br2 OR bromine (water) OR bromine (in CCl4 / organic solvent) If M1, has no reagent or an incorrect reagent, CE=0. Ignore ‘acidified’.

M2 Isomer 1: decolourised / goes colourless / loses its colour For M1 penalise Br (or incorrect formula of other correct reagent), but mark on.

M3 Isomer 2: remains orange / red / yellow / brown / the same OR no reaction / no (observable) change OR reference to colour going to the cyclopentane layer

For M1, it must be a whole reagent and / or correct formula. If oxidation state given in name, it must be correct. If ‘manganate’ OR ‘manganate(IV)’ or incorrect formula, penalise M1, but mark on.

Alternatives : potassium manganate(VII)

M1 KMnO4 in acid M2 colourless M3 purple

M1 KMnO4 in alkali / neutral M2 brown solid M3 purple

Credit for the use of iodine

M1 iodine (solution / in KI) M2 colourless M3 (brown) to purple (credit no change)

Credit for the use of concentrated H2SO4

M1 concentrated H2SO4 M2 brown M3 no change / colourless Ignore ‘goes clear’.

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Ignore ‘nothing (happens)’. Ignore ‘no observation’. No credit for combustion observations.

3

(c) (i) (Both infrared spectra show an absorption in range) 1620 to 1680 (cm−1) Ignore reference to other ranges (eg for C–H or C–C).

1

(ii) The fingerprint (region) / below 1500 cm−1 will be different or its fingerprinting will be different

OR

different absorptions / peaks are seen (in the region) below 1500 cm−1 (or a specified region within the fingerprint range)

Allow the words ‘dip’ OR ‘spike’ OR ‘low transmittance’ as alternatives for absorption. QoL

1

(d)

All bonds must be drawn. Ignore bond angles.

1

(e) (i) M1 Electrophilic addition M1 both words needed.

Penalise one mark from their total if half-headed arrows are used.

M2 must show an arrow from the double bond towards the H atom of the H–Br molecule

M2 Ignore partial negative charge on the double bond.

M3 must show the breaking of the H–Br bond M3 Penalise incorrect partial charges on H–Br bond and penalise formal charges.

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M4 is for the structure of the tertiary carbocation Penalise M4 if there is a bond drawn to the positive charge. Penalise once only in any part of the mechanism for a line and two dots to show a bond.

M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged carbon atom of either a secondary or a tertiary carbocation

For M5, credit attack on a partially positively charged carbocation structure but penalise M4. Max 3 of any 4 marks in the mechanism for wrong organic reactant or wrong organic product (if shown) or secondary carbocation. Max 2 of any 4 marks in the mechanism for use of bromine. Do not penalise the correct use of 'sticks”.


(ii) M1 Reaction goes via intermediate carbocations / carbonium ions M1 is a lower demand mark for knowledge that carbocations are involved.

M2 (scores both marks and depends on M1)

Tertiary carbocation / carbonium ion is more stable (than the secondary carbocation / carbonium ion)

OR

Secondary carbocation / carbonium ion is less stable (than the tertiary carbocation / carbonium ion)

M2 is of higher demand and requires the idea that the secondary carbocation is less stable or the tertiary carbocation is more stable. Reference to incorrect chemistry is penalised. A carbocation may be defined in terms of alkyl groups / number of carbon atoms, rather than formally stated.

2

(f) M1 Elimination M1 credit ‘base elimination’ but no other qualifying prefix.

Penalise one mark from their total if half-headed arrows are used.

M2 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to a correct H atom

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Penalise M2 if covalent KOH

M3 must show an arrow from a correct C–H bond adjacent to the C–Br bond to a correct C–C bond. Only award if an arrow is shown attacking the H atom of a correct adjacent C–H bond (in M2)

M4 is independent provided it is from their original molecule BUT penalise M2, M3 and M4 if nucleophilic substitution shown

Award full marks for an E1 mechanism in which M2 is on the correct carbocation

NB The arrows here are double-headed Penalise M4 for formal charge on C or Br of the C–Br bond or incorrect partial charges on C–Br. Penalise M4 if an additional arrow is drawn from the Br of the C–Br bond to, for example, K+. Ignore other partial charges. Penalise once only in any part of the mechanism for a line and two dots to show a bond. Max 2 of any 3 marks in the mechanism for wrong reactant or wrong organic product (if shown) or a correct mechanism that leads to the alkene 2-methylbut-2-ene. Credit the correct use of “sticks” for the molecule except for the C–H being attacked.

M5 hydroxide ion behaves as a base / proton acceptor / electron pair donor / lone pair donor

Penalise M5 if ‘nucleophile’. 5

[21]

Q18. (a) (i) M1 (Yield) increases / goes up / gets more

If M1 is blank, mark on and seek to credit the correct information in the explanation. If M1 is incorrect CE=0 for the clip.

M2 The (forward) reaction / to the right is exothermic or gives out / releases heat OR The reverse reaction / to the left is endothermic or takes in / absorbs heat M3 depends on a correct statement for M2

M3 depends on correct M2 and must refer to temperature / heat The (position of ) equilibrium shifts / moves left to right to oppose the decrease in temperature For M3, the equilibrium shifts / moves to release heat OR to raise the temperature OR to heat up the reaction.

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3

(ii) M1 Concentration(s) (of reactants and products) remain or stay constant / the same

For M1 credit [ ] for concentration.

M2 Forward rate = reverse / backward rate Not “equal concentrations”. Not “concentrations is / are the same”. Not “amount”. Ignore “dynamic” and ignore “speed”. Ignore “closed system”. It is possible to score both marks under the heading of a single feature.

2

(b) KBr + H2SO4 KHSO4 + HBr Credit this equation in its ionic form. Ignore state symbols. Credit multiples.

1

(c) M1 SO2 identified

M2 correctly balanced equation (would also gain M1) Credit M2 equation in its ionic form. Ignore state symbols.

2HBr + H2SO4 Br2 + SO2 + 2H2O Credit multiples. Not H2SO3 on the right-hand side.

Mark M3 independently M3 Oxidising agent OR electron acceptor OR oxidant OR to oxidise the bromide (ion) / HBr

M3 Not “electron pair acceptor”. 3

(d) (i) M1 Electrophilic addition

M1 both words required. For the mechanism M3 Penalise incorrect partial charges on O − H bond and penalise formal charges

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Ignore partial negative charge on the double bond. M5 Not HSO4

–

For M5, credit as shown or −:OSO3H ONLY with the negative charge anywhere on this ion OR correctly drawn out with the negative charge placed correctly on oxygen.

M2 must show an arrow from the double bond towards the H atom of the H − O bond / HO on a compound with molecular formula for H2SO4

M2 could be to an H+ ion and M3 an independent O − H bond break on a compound with molecular formula for H2SO4

Max any 3 of 4 marks for a correct mechanism using the wrong organic reactant or wrong organic product (if shown) or a primary carbocation.

M3 must show the breaking of the O − H bond on H2SO4

Penalise once only in any part of the mechanism for a line and two dots to show a bond.

M5 must show an arrow from the lone pair of electrons on the correct oxygen of the negatively charged ion towards the positively charged carbon atom on their carbocation

Credit the correct use of “sticks”. For M5, credit attack on a partially positively charged carbocation structure, but penalise M4


(ii) Hydrolysis Credit “(nucleophilic) substitution” but do not accept any other prefix. Credit phonetic spelling.

1

(iii) Catalyst 1

[16]

Q19. (a) Structure for 3-methylbut-1-ene

H2C=CHCH(CH3)2


1

(b) Structure for 2-methylpropan-2-ol

(CH3)3COH Any correct structural representation. Credit “sticks”.

1

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(c) Structure for propene

H2C=CHCH3


1

(d) Structure for 2-aminobutane

CH3CH2CH(NH2)CH 3

Any correct structural representation. Credit “sticks”.

1 [4]

Q20. (a) (i) Structure of (Z)-but-2-enenitrile with or without either or both of the CH3 and

the CN groups displayed

Penalise C−NC Do not penalise C−H3C Ignore bond angles.

1

(ii) Restricted rotation / no (free) rotation about the double bond / about the C=C OR does not rotate (about the double bond)

Must use the word rotate / rotation. 1

(b) Repeating unit of polyalkene

All the bonds relevant to the unit must be drawn out including those on either side of the unit. There is no need to expand either the CH3 or the CN Penalise C−NC Penalise “sticks”. Ignore brackets. Penalise “n”

1

(c) Feature 1 Absorption / peak in the range 2220 to 2260 cm−1 or specified value in this range or marked correctly on spectrum

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and (characteristic absorption / peak for) C≡N / CN group / nitrile / cyanide group

Allow the words “dip” OR “spike” OR “trough” OR “low transmittance” as alternatives for absorption. Allow a peak at 2200 cm−1 to 2220 cm−1 in this case.

Feature 2 Absorption / peak in the range 1620 to 1680 cm−1 or specified value in this range or marked correctly on spectrum and (characteristic absorption / peak for) C=C group / alkene / carbon-carbon double bond

Ignore reference to other absorptions eg C-H Either order.

2 [5]

Q21. (a) M1 electrophilic addition

For M1, both words required Accept phonetic spelling

For the mechanism M2 Ignore partial negative charge on the double bond


M3 Penalise partial charges on H–Br bond if wrong way and penalise formal charges

M3 must show the breaking of the H–Br bond Penalise once only in any part of the mechanism for a line and two dots to show a bond

M5 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the correct (positively charged) carbon atom

Maximum any 3 of 4 marks for the mechanism for wrong (organic) reactant OR wrong organic product (if shown) OR primary carbocation Accept the correct use of sticks

NB These are double-headed arrows 5

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(b) M1 Nucleophilic substitution For M1, both words required Accept phonetic spelling

For the mechanism Penalise M2 if NH3 is negatively charged

M2 must show an arrow from the lone pair of electrons on the nitrogen atom of an ammonia molecule to the correct C atom

Penalise M3 for formal charge on C of the C−Br or incorrect partial charges on C−Br Penalise M3 for an additional arrow from the Br to something else

M3 must show the movement of a pair of electrons from the C–Br bond to the Br atom. Mark M3 independently provided it is from their original molecule

The second mole of ammonia is not essential for M5; therefore ignore any species here

M4 is for the structure of the alkylammonium ion, which could be a condensed formula. A positive charge must be shown on / or close to, the N atom

Penalise once only for a line and two dots to show a bond

M5 is for an arrow from the N–H bond to the N atom Maximum any 3 of 4 marks for the mechanism for wrong organic reactant OR wrong organic product if shown

Award full marks for an SN1 mechanism in which M2 is the attack of the ammonia on the intermediate carbocation

Accept the correct use of “sticks”


(c) M1 (addition) polymerisation OR poly-addition Ignore “additional” Credit polyprop-1-ene and polypropylene

M2 poly(propene) / polypropene Penalise “condensation polymerisation”

2

(d)

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M1 must show an arrow from the lone pair on the oxygen of a negatively charged hydroxide ion to a correct H atom

Penalise M3 for formal charge on C of C–Br or incorrect partial charges on C−Br.

M2 must show an arrow from a correct C–H bond adjacent to the C–Br bond to the appropriate C–C bond. Only award if an arrow is shown attacking the H atom of a correct C−H bond in M1

Ignore other partial charges Penalise once only in any part of the mechanism for a line and two dots to show a bond

M3 is independent provided it is from their original molecule, but CE=0 if nucleophilic substitution

Maximum any 2 of 3 marks for wrong organic reactant

Award full marks for an E1 mechanism in which M3 is on the correct carbocation.

Accept the correct use of “sticks” for the molecule except for the C–H being attacked


[15]

Q22. (a) Position(al) (isomerism)

1

(b)

Penalise one mark from their total if half-headed arrows are used


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M1 Ignore partial negative charge on the double bond.

M2 must show the breaking of the H–Br bond. M2 Penalise partial charges on H–Br bond if wrong way and penalise formal charges

M3 is for the structure of the secondary carbocation. Penalise M3 if there is a bond drawn to the positive charge

M4 must show an arrow from the lone pair of electrons on the negatively charged bromide ion towards the positively charged carbon atom of either a primary or secondary carbocation.

Penalise once only in any part of the mechanism for a line and two dots to show a bond Maximum any 3 of 4 marks for wrong reactant or primary carbocation. If Br2 is used, maximum 2 marks for their mechanism Do not penalise the use of “sticks”


(c)

Penalise one mark from their total if half-headed arrows are used

M1 must show an arrow from the lone pair on oxygen of a negatively charged hydroxide ion to a correct H atom


M2 must show an arrow from a C–H bond adjacent to the C–Br bond towards the appropriate C–C bond. Only award if an arrow is shown attacking the H atom of an adjacent C–H (in M1)

M3 is independent provided it is from their original molecule. Penalise M3 for formal charge on C of the C–Br or incorrect partial charges on C–Br Penalise M3 if an extra arrow is drawn from the Br of the C–Br bond to, for example, K+

Ignore other partial charges Penalise once only in any part of the mechanism for a line and two dots to show a bond. Maximum any 2 of 3 marks for wrong reactant or wrong product (if shown) or a mechanism that leads to but-1-ene

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Accept the correct use of “sticks” for the molecule except for the C–H being attacked

Award full marks for an E1 mechanism in which M2 is on the correct carbocation.


[8]

Q23. (a) Benzene-1,2-dicarboxylic acid

Allow 1,2-benzenedicarboxylic acid 1

(b)

Must show all bonds including trailing bonds Ignore n

1

(c) (i) 2 C2H5OH NB Two ethanols

1

H2O but only one water

1

(ii) 6 or six 1

(iii)

Ignore overlap with O to the left or H to the right, but must only include this one carbon. either or allow both (as they are identical)

1

(d)

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Allow + on C or O in 1

Dot must be on O in radical 1

(e) (i) Rate = k[DEP] Must have brackets but can be ( )

1

(ii) Any two of

• experiment repeated/continued over a long period

• repeated by independent body/other scientists/avoiding bias

• investigate breakdown products

• results made public Not just repetition Ignore animal testing

2 max [11]

Q24. (a) (i)

1

(ii)

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1

(iii) hydrogen bonding (do not allow H-bonding) QWC do not penalise any error twice.

1

(b) (i)

1

(ii)

1

(iii) Isomer must be saturated or must not contain a double bond 1

(c)

2

(d) (i) heat/reflux with aqu NaOH 1

poly(alkene) is inert/ no reaction 1

polyamide is hydrolysed (or undergoes hydrolysis) to form acid salt and alcohol QWC

1

(ii) e.g combustion 1

heat energy produced 1

toxic gases produced 1

[14]

Q25.

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D [1]

Q26. D

[1]

Q27. (a) M1 fermentation

1

M2 dehydration or elimination 1

(b) (i) yeast OR zymase OR an enzyme 1

(ii) concentrated sulphuric or phosphoric acid (penalise aqueous or dilute as a contradiction)

1

(c) (i) primary or 1° 1

(ii) sugar or glucose or ethanol is renewable OR ethanol does not contain sulphur-containing impurities OR ethanol produces less pollution or is less smoky or less CO/C

(the objective is a positive statement about ethanol) (penalise the idea that ethanol is an infinite source or vague statements that ethanol has less impurities) (penalise the idea that ethanol produces no pollution)

1

(d) C2H6 → C2H4 + H2 1

(e) Addition (ignore self or chain as a preface to “addition “) (penalise additional)

1 [8]

Q28. (a) (i) moles of C2F2 = 0.40 mark independently from HC1

1

moles of HC1 = 0.80 not consequential 1

(ii)

wrong Kc means they can only

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score for units in (iii) consequ

on their Kc 1

(iii) 1

= 0.35 1

mol dm–3

1

(b) (i) increase 1

(ii) decrease 1

(c) addition or radical 1

[9]

Q29. (a) (i) An appropriate alkene; CH3CH2CHCH2 or (CH3)2CCH2

1

Isomer 1 1

Isomer 2 1

Position isomerism 1

Mechanism

electrophilic attack and electron shift to Br (Unless H+ used) 1

carbocation 1

reaction with carbocation [Allow mechanism marks for the alkene CH3CHCHCH3] [Allow one mark if mechanism for minor product given]

1

(ii) An appropriate carbonyl; CH3CH2CHO 1

Mechanism nucleophilic attack and electron shift to O 1

anion intermediate

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1

reaction with anion [Allow mechanism marks for the carbonyl (CH3)2CO]

1

Isomer 1 1

Isomer 2 1

Optical isomerism NB Isomer structures must be tetrahedral NB Penalise “stick” structures once in part (a)

1

(b) QoL Large charge on carbonyl carbon atom due to bonding to O and Cl

1

Nucleophiles have electron pairs which can be donated 1

Equation Species 1

Balanced 1

[18]

Q30. (a) (i) Electrophilic addition

(Both words required) 1

(ii) M1 the reaction to form 1-bromopropane goes via the primary carbocation OR 1o carbocation

OR via

M2 primary carbocations are less stable than secondary carbocations (Credit converse arguments for M1 and M2 i.e. the reaction to form 2-bromopropane goes via the secondary carbocation , M1, and secondary carbocations are more stable than primary carbocations, M2) (Accept the use of “carbonium ions” as an alternative to carbocation)

1

(b) M1 NaOH OR KOH OR correct name 1

M2 aqueous or solution in water (ignore heat, reflux etc.) (Penalise M1 for hydroxide ion alone, but mark on and credit

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M2) (Credit M2 ONLY for H2O as reagent and heat / warm / T=50 to 100oC) (NaOH(aq) scores M1 and M2 provided it is not contradicted) (Penalise M2 if NaOH(aq) followed by concentrated or ethanol) (Penalise M1 and M2 if followed by acid)

1

(c) Ethanolic OR alcoholic OR CH3CH2OH / CH3OH solvent OR aqueous ethanol/alcohol OR higher temperature (must be comparative)

(Ignore heat or heat under reflux) (Credit part (c) independently from part (b)) (Penalise “ethanoic”)

1

(d) (i) Secondary OR 2o

1

(ii)

M1 arrow from double bond to H of H – O bond M2 arrow from bond to oxygen atom to show H – O bond breakage M4 arrow from lone pair of electrons to carbon atom of carbocation

(Penalise M1 if arrow goes to H2SO4 or to formal positive charge on H, but ignore partial charges on sulphuric acid unless wrong) (Credit M2 for H+ ion) (For M4, accept negative charge anywhere on the ion)

4

(iii) Catalyst ONLY (Ignore homogeneous, heterogeneous)

1 [12]

Q31. A

[1]

Q32. B

[1]

Q33. (a) (i)

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(ii) restricted rotation OR no rotation OR cannot rotate (1) 3

(b) (i) Mechanism:

M1 and M2 independent Curly arrows must be from a bond or a lone pair Do not penalise sticks

Penalise M1 if precedes (penalise this once) Penalise incorrect δ+ δ– for M2 Penalise + on C atom for M2 Only allow M1 for incorrect haloalkane

Role of the hydroxide ion: nucleophile (1) electron pair donor lone pair donor

NOT nucleophilic substitution

(ii) Mechanism:

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Only allow M1 and M2 for incorrect haloalkane unless RE on (i) + charge on H on molecule, penalise M1 M3 independent M2 must be to correct C–C M1 must be correct H atom Credit M1 and M2 via carbocation mechanism

No marks after any attack of C by OH–

Role of the hydroxide ion: base (1) proton acceptor accepts H+

7 [10]

Q34. (a) (i)

If wrong carbocation, lose structure mark If wrong alkene, lose structure mark Can still score ¾ i.e. penalise M3 Penalise M2 if polarity included incorrectly no bond between H and Br bond is shown as or

(ii) credit secondary carbocation here if primary carbocation has been used in (i)

Ignore attack on this carbocation by 5

(b) (i) Structure:

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No credit for propan-1-ol even when named correctly Credit propane-2-ol

Name: propan-2-ol (1) Not 2-hydroxypropane

(ii) Name of mechanism: nucleophilic substitution (1) (both words) (NOT SN1 orSN2)

Mechanism:

penalise incorrect polarity on C‑Br (M1) Credit the arrows even if incorrect haloalkane If SN1, both marks possible

5

(c) (i) elimination (1) Ignore nucleophylic elimination Penalise electrophilic elimination

(ii) base (1) OR proton acceptor NOT nucleophile (base)

2 [12]

Q35.

(a) May circle 4 C’s separately

1

(b)

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Ignore δ+ and δ- unless wrong

4

(c) Reagent: H2O or water OR steam, Or dilute sulphuric acid (1) Condition: heat, or warm, or boil or reflux [50-100°C] (1) Name of compound C: 2-methylbutan-2-ol (1)

Allow 2-methylbutane-2-ol Penalise hydroxy-2-methylbutane and 2-methylbut-2-ol once only in the paper

3

(d) Identity of alcohol D: 2-methylbutan-1-ol (1), OR its structure, could describe structure

Explanation: C formed via t-carbocation; D via p-carbocation, (1) tertiary more stable than primary (1)

If have wrong carbocation can still score stability mark 3

[11]

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Amount of substance exam pack 1 new spec

Name: ________________________

Class: ________________________

Date: ________________________

Time: 122 minutes

Marks: 96 marks

Comments:

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Q1. The diagram shows some compounds made from a halogenoalkane.

(a) Draw the displayed formula of compound J.

(1)

(b) Name the mechanism for Reaction 2 and give an essential condition used to ensure that CH3CH2CH2NH2 is the major product.


Condition ___________________________________________________________ (2)

(c) Calculate the mass, in grams, of CH3CH2CH2NH2 produced from 25.2 g of CH3CH2CH2Br in Reaction 2 assuming a 75.0% yield.


Mass ____________________ g (3)

(d) When Reaction 2 is carried out under different conditions, a compound with molecular formula C9H21N is produced.

Draw the skeletal formula of the compound.

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Identify the functional group in the compound including its classification.

Skeletal formula

Functional group including classification ____________________ (2)

(e) Identify the reagent and conditions used in Reaction 3.

___________________________________________________________________ (1)

(f) Name and outline a mechanism for Reaction 3.


Mechanism


Q2. Which of these contains the greatest number of atoms?

A 127 mg of iodine

B 1.54 × 10−4 kg of phosphorus

C 81.0 mg of carbon dioxide

D 1.70 × 10−4 kg of ammonia (Total 1 mark)

Q3. Two sealed flasks with the same volume are left side by side.

Flask A contains 4.0 × 10−3 mol of methane.

Flask B contains 340 mg of a different gas.

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Both gases are at the same temperature and pressure.

Which gas could be in Flask B?

A CH2Cl2

B HBr

C Kr

D PF3

(Total 1 mark)

Q4. A sample of 2.0 mol dm−3 acid has a volume of 100 cm3

What volume of water, in cm3, should be added to this acid to dilute the sample to a concentration of 1.5 mol dm−3?

A 25

B 33.3

C 50

D 66.7 (Total 1 mark)

Q5. Which sample contains the most molecules?

The Avogadro constant, L = 6.022 x 1023 mol−1

A 2.10 × 1022 molecules of methane, CH4

B 1.00 g of oxygen, O2

C 65.0 mg of hydrogen, H2

D 0.0300 mol of ethane, C2H6

(Total 1 mark)

Q6. A volumetric flask was used to prepare 250 cm3 of a solution.

The solute was added from a plastic weighing container.

Mass

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/ g

Weighing container with solute 10.13

Weighing container after solute added to volumetric flask 4.48

Each reading from the balance has an uncertainty of ±0.005 g

What is the percentage uncertainty in the mass of the solute used?

A 0.09%

B 0.11%

C 0.18%

D 0.22% (Total 1 mark)

Q7. What is the burette reading for this transparent liquid?

A 24.10 cm3

B 24.30 cm3

C 25.70 cm3

D 25.90 cm3

(Total 1 mark)

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Q8. An experiment was carried out to determine the relative molecular mass (Mr) of a volatile hydrocarbon X that is a liquid at room temperature.

A known mass of X was vaporised at a known temperature and pressure and the volume of the gas produced was measured in a gas syringe.

Data from this experiment are shown in the table.

Mass of X 194 mg

Temperature 373 K

Pressure 102 kPa

Volume 72 cm3

(a) Calculate the relative molecular mass of X.

Show your working.


The gas constant, R = 8.31 J K−1 mol−1

Relative molecular mass _________________________________________ (5)

(b) Analysis of a different hydrocarbon Y shows that it contains 83.7% by mass of carbon.

Calculate the empirical formula of Y.

Use this empirical formula and the relative molecular mass of Y (Mr = 86.0) to calculate the molecular formula of Y.

Empirical formula ____________________________________________________

Molecular formula ____________________________________________________ (4)

(Total 9 marks)

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Q9. Ethanedioic acid (H2C2O4) is a diprotic acid. Beekeepers use a solution of this acid as a pesticide.

A student carried out a titration with sodium hydroxide solution to determine the mass of the acid in the solution. The student repeated the titration until concordant titres were obtained.

H2C2O4(aq) + 2NaOH(aq) ⟶ Na2C2O4(aq) + 2H2O(l)

(a) The student found that 25.0 cm3 of the ethanedioic acid solution reacted completely with 25.30 cm3 of 0.500 mol dm−3 sodium hydroxide solution.

Calculate the mass, in mg, of the acid in 25.0 cm3 of this solution.

Mass of acid = ____________________ mg (4)

(b) The student used a wash bottle containing deionised water when approaching the end-point to rinse the inside of the conical flask.

Explain why this improved the accuracy of the titration.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(c) Give the meaning of the term concordant titres.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(Total 6 marks)

Q10. What is the empirical formula of an oxide of nitrogen that contains 26% nitrogen by mass?

A NO2

B N2O3

C N2O5

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D N4O5

(Total 1 mark)

Q11. A 20.0 cm3 sample of a 0.400 mol dm−3 aqueous solution of a metal bromide (MBrn) reacts exactly with 160 cm3 of 0.100 mol dm−3 aqueous silver nitrate.

What is the formula of the metal bromide?

A MBr

B MBr2

C MBr3

D MBr4

(Total 1 mark)

Q12. What is the mass, in mg, of carbon formed when 3.0 × 10−3 mol of propene undergoes incomplete combustion?

2C3H6 + 3O2 ⟶ 6C + 6H2O

A 9.0 × 10−3

B 3.6 × 10−2

C 1.08 × 102

D 2.16 × 102

(Total 1 mark)

Q13. What is the empirical formula of 4-hydroxypent-2-ene?

A C5H12O

B C5H10O

C CH2O

D C5H9OH (Total 1 mark)

Q14.

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25.0 cm3 samples of NaOH solution were taken by pipette from a beaker. These were then titrated with an aqueous solution of ethanoic acid. The concentration of ethanoic acid calculated from the experimental results was found to be lower than the actual value.

Which of these could explain the difference?

A Rinsing the pipette with distilled water before filling with NaOH

B Rinsing the burette with distilled water before filling with ethanoic acid

C Rinsing the walls of the conical flask with distilled water during the titration

D Rinsing the beaker with distilled water before filling with NaOH (Total 1 mark)

Q15. The equation for the hydrogenation of ethyne is

C2H2 + 2H2 ⟶ C2H6

The experimental yield is 65.0%.

What is the mass in grams of ethane that can be produced from 16.20 g of hydrogen?

A 42.53 g

B 78.98 g

C 121.5 g

D 527.7 g (Total 1 mark)

Q16. Which of these contains the most molecules?

A 0.0311 kg of carbon dioxide, CO2

B 29.6 g of carbon monoxide, CO

C 2.22 × 104 mg of oxygen, O2

D 13.3 g of ozone, O3

(Total 1 mark)

Q17. The maximum uncertainty when weighing 0.250 g on a balance was 0.001 g.

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What is the percentage uncertainty?

A 4.0%

B 0.4%

C 0.8%

D 250% (Total 1 mark)

Q18. This question is about reactions of calcium compounds.

(a) A pure solid is thought to be calcium hydroxide. The solid can be identified from its relative formula mass.

The relative formula mass can be determined experimentally by reacting a measured mass of the pure solid with an excess of hydrochloric acid. The equation for this reaction is

Ca(OH)2 + 2HCl CaCl2 + 2H2O

The unreacted acid can then be determined by titration with a standard sodium hydroxide solution.

You are provided with 50.0 cm3 of 0.200 mol dm−3 hydrochloric acid. Outline, giving brief practical details, how you would conduct an experiment to calculate accurately the relative formula mass of the solid using this method.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (8)

(b) A 3.56 g sample of calcium chloride was dissolved in water and reacted with an excess of sulfuric acid to form a precipitate of calcium sulfate.

The percentage yield of calcium sulfate was 83.4%.

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Calculate the mass of calcium sulfate formed. Give your answer to an appropriate number of significant figures.

Mass of calcium sulfate formed = ____________ g (3)

(Total 11 marks)

Q19. After reaction of some zinc metal with excess sulfuric acid, a student collected 40.8 g of ZnSO4.7H2O crystals. The yield of crystals was 70.0%.

What was the original mass of zinc used?

A 9.28 g

B 13.3 g

C 23.6 g


Q20. Which of the following contains the most chloride ions?

A 15 cm3 of 3.40 × 10−2 mol dm−3 aluminium chloride solution

B 30 cm3 of 5.50 × 10−2 mol dm−3 calcium chloride solution

C 40 cm3 of 2.30 × 10−2 mol dm−3 hydrochloric acid

D 45 cm3 of 2.20 × 10−2 mol dm−3 sodium chloride solution (Total 1 mark)

Q21. 2.40 g of an explosive, J, contains 0.473 g of nitrogen. J also contains 33.8% carbon and 1.41% hydrogen by mass. The remainder of J is oxygen.

What is the empirical formula of J?

A C4HNO2

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B CH2N2O

C C2HNO2

D CHNO (Total 1 mark)

Q22. What is the number of atoms in 0.0100 mol of NH3? (The Avogadro constant L = 6.022 × 1023 mol−1)

A 6.02 × 1025

B 1.20 × 1023

C 1.81 × 1022

D 2.41 × 1022

(Total 1 mark)

Q23. A 4.85 g sample of anhydrous sodium sulfate is dissolved in water and the solution made up to 250 cm3 in a volumetric flask.

What is the concentration in mol dm−3 of sodium sulfate in the solution?

A 0.0341

B 0.137

C 0.163


Q24. What is the volume of 0.200 mol dm−3 Ba(OH)2 (aq) required to neutralise exactly 30.0 cm3 of 0.100 mol dm−3 HCl(aq)?

A 150.0 cm3

B 75.0 cm3

C 15.0 cm3

D 7.50 cm3

(Total 1 mark)

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Q25. Which reaction has the largest atom economy for the production of hydrogen?

A C + H2O ⟶ CO + H2

B Zn + 2HCl ⟶ ZnCl2 + H2

C CH4 + H2O ⟶ CO + 3H2

D CO + H2O ⟶ CO2 + H2

(Total 1 mark)

Q26. This question is about a toxic chloroalkane, X, that has a boiling point of 40 °C.

A student carried out an experiment to determine the Mr of X by injecting a sample of X from a hypodermic syringe into a gas syringe in an oven at 97 °C and 100 kPa. The student’s results are set out in Table 1 and Table 2.

Table 1

Mass of hypodermic syringe filled with X before injection / g 10.340

Mass of hypodermic syringe with left over X after injection / g 10.070

Mass of X injected / g

Table 2

Volume reading on gas syringe before injection of X / cm3 0.0

Volume of X in gas syringe after injection of X / cm3 105.0

Volume of X / cm3

(a) Complete Table 1 and Table 2 by calculating the mass and volume of X. (1)

(b) X is known to be one of the following chloroalkanes: CCl4CHCl3CH2Cl2 or CH3Cl

Justify this statement by calculating a value for the Mr of X and use your answer to suggest the most likely identity of X from this list.

Give your answer for the Mr of X to an appropriate precision. (The gas constant R = 8.31 J K−1 mol−1)

Mr of X

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Mr of X = ______________________

Identity of X (If you have been unable to calculate a value for Mr, you may assume that the Mr value is 52. This is not the correct value).

Identity of X = __________________ (5)

(c) Suggest a reason, other than apparatus inaccuracy, why the Mr value determined from the experimental results differs from the actual Mr. Explain your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) Suggest, with a reason, an appropriate safety precaution that the student should take when using the toxic chloroalkane, X, in the experiment.

Safety precaution ____________________________________________________

___________________________________________________________________

Reason ____________________________________________________________

___________________________________________________________________ (2)

(Total 10 marks)

Q27. A measuring cylinder has an uncertainty of ±5 cm3.

What is the minimum volume of liquid that can be measured if the percentage error in the volume is to be less than 0.20%?

A 0.025 dm3

B 0.25 dm3

C 2.5 dm3

D 25 dm3

(Total 1 mark)

Q28. 130 cm3 of oxygen and 40 cm3 of nitrogen, each at 298 K and 100 kPa, were placed into an evacuated flask of volume 0.50 dm3.

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What is the pressure of the gas mixture in the flask at 298 K?

A 294 kPa

B 68.0 kPa

C 34.0 kPa

D 13.7 kPa (Total 1 mark)

Q29. A student is provided with 5.00 cm3 of 1.00 mol dm−3 ammonia solution. The student was asked to prepare an ammonia solution with a concentration of 0.050 mol dm−3

What volume of water should the student add?

A 45.0 cm3

B 95.0 cm3

C 100 cm3

D 995 cm3

(Total 1 mark)

Q30. Phenylethanone can be prepared by the reaction between ethanoyl chloride and benzene.

In a preparation, with an excess of benzene, the mass of ethanoyl chloride (Mr = 78.5) used was 5.7 × 10−2 kg.

The percentage yield of phenylethanone was 62%.

What mass, in grams, of phenylethanone was produced?

A 35 g

B 54 g

C 87 g

D 102 g (Total 1 mark)

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Q31. A 385 cm3 sample of carbon dioxide at 100 kPa and 25 °C was mixed with 2.89 × 10−2 mol of argon. The gas constant, R = 8.31 J K−1 mol−1

What is the mole fraction of carbon dioxide in the mixture?

A 0.35

B 0.46

C 0.54


Q32. A solution of lead(ll) chloride (Mr = 278.2) contains 1.08 g of PbCl2 in 100 cm3 of solution. In this solution, the lead(ll) chloride is fully dissociated into ions.

What is the concentration of chloride ions in this solution?

A 3.88 × 10−3 mol dm−3

B 7.76 × 10−3 mol dm−3

C 3.88 × 10−2 mol dm−3

D 7.76 × 10−2 mol dm−3

(Total 1 mark)

Q33. The equation for the reaction between zinc and hydrochloric acid is

Zn + 2HCl ⟶ ZnCl2 + H2

What is the minimum mass, in mg, of zinc (Ar = 65.4) needed to react with 50.0 cm3 of 1.68 mol dm−3 hydrochloric acid?

A 2.75

B 5.49

C 2.75 × 103

D 5.49 × 103

(Total 1 mark)

Q34. Copper can be produced from rock that contains CuFeS2

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(a) Balance the equations for the two stages in this process.

.....CuFeS2 + .....O2 + .....SiO2 ⟶ .....Cu2S + .....Cu2O + .....SO2 + .....FeSiO3

.....Cu2S + .....Cu2O ⟶ .....Cu + .....SO2

(2)

(b) Suggest two reasons why the sulfur dioxide by-product of this process is removed from the exhaust gases.

Reason 1 ___________________________________________________________

___________________________________________________________________

___________________________________________________________________

Reason 2 ___________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) A passenger jet contains 4050 kg of copper wiring.

A rock sample contains 1.25% CuFeS2 by mass.

Calculate the mass, in tonnes, of rock needed to produce enough copper wire for a passenger jet. (1 tonne = 1000 kg)

Mass of rock ____________________ tonnes (4)

(d) Copper can also be produced by the reaction of carbon with copper(II) oxide according to the equation

2CuO + C ⟶ 2Cu + CO2

Calculate the percentage atom economy for the production of copper by this process.


Percentage atom economy ____________________

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Q35. This question is about atomic structure.

(a) Write the full electron configuration for each of the following species.

Cl−________________________________________________________________

Fe2+_______________________________________________________________ (2)

(b) Write an equation, including state symbols, to represent the process that occurs when the third ionisation energy of manganese is measured.

___________________________________________________________________

___________________________________________________________________ (1)

(c) State which of the elements magnesium and aluminium has the lower first ionisation energy.

Explain your answer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(d) A sample of nickel was analysed in a time of flight (TOF) mass spectrometer. The sample was ionised by electron impact ionisation. The spectrum produced showed three peaks with abundances as set out in the table.

m/z Abundance / %

58 61.0

60 29.1

61 9.9

Give the symbol, including mass number, of the ion that would reach the detector first in the sample.

Calculate the relative atomic mass of the nickel in the sample.

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Give your answer to one decimal place.

Symbol of ion _______________________________________________________

Relative atomic mass _________________________________________________ (3)

(Total 9 marks)

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Mark schemes

Q1. (a)

Must be displayed

1

(b) Nucleophilic substitution 1

Excess NH3

Ignore aqueous, alcoholic, conc, dil, temp, heat, pressure 1

(c) Amount of CH3CH2CH2Br 25.2/122.9 (=0.205) (mol) M1

Amount of CH3CH2CH2NH2 M1 × 0.75 (= 0.154) (mol) M2

Mass CH3CH2CH2NH2 M2 × 59.0 = 9.07g Must be 3sf M3

If either Mr incorrect or used incorrectly then only award 1 mark for 75% yield calculation (ignore rounding to 123 for CH3CH2CH2Br)

OR Max mass amine = M1 × 59.0 (= 12.1) (g) Actual mass = M2 × 0.75 = 9.07g Must be 3sf

Allow 9.09 but if 9.08 check for AE 18.9 scores 1 for 75%

(d)

Must be skeletal Ignore lone pair

1

tertiary amine or 3° amine (only award if a tertiary amine shown) 1

(e) NaOH/ ethanol or KOH / ethanol (both required) NOT aqueous Ignore heat, temp, conc., dil,

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Accept alcoholic for ethanol 1

(f) (Basic) Elimination

Also credit E1 mechanism

1

M1 arrow from lone pair on O of hydroxide to correct H (or to space mid way between hydroxide O and H)

M2 arrow from C-H bond to C-C bond following attack by OH− on the correct H

M3 arrow from C-Br bond to Br

If nucleophilic substitution shown then allow M3 only in mechanism

If wrong haloalkane used then Max 2 for mechanism M3 curly arrow for loss of Br− & structure of carbocation M1 arrow from lone pair on O of hydroxide to H (or to space mid way between hydroxide O and H) (same as E2) M2 arrow from C-H bond to C-C bond (same as E2)

3 [13]

Q2. D

[1]

Q3. A

[1]

Q4. B

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[1]

Q5. A

[1]

Q6. C

[1]

Q7. B

[1]

Q8. (a) Stage 1

M1 1

M2 1

M3 = 0.0024 / 0.00237 / 0.002369 / 0.0023693 .. 1

Stage 2

M4 1

M5 = 82 (2sf only) 1

As this is an extended response question, each separate step of correct working is required in M1–M5 Correct answer with no working scores 2 marks M1 – If expression not written out, M1 could score from a correct expression for M2 (even if unit conversions are not correct for M2) M2 – allow an expression that gives correct value for M3 M3 should be at least 2sf (do not allow 0.0023 but do allow 0.00236) M4 must show 0.194 or 194 × 10−3 in working to score M5 must be 2sf ECF: • No ECF within either stage 1 or stage 2 (except for

transcription errors) • Allow ECF from stage 1 into stage 2, i.e for M4 and M5

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based on incorrect M3, (but if expression for M4 is inverted, cannot score M5)

• (Note that if 72 × 10−3 used in M2, then M3 = 2.4, M5 = 0.082)

Ignore units for M3 and M5 Note that if T = 273 + 373 = 646, M5 = 140 (2sf)

(b) M1 dividing %s by relative atomic masses C = 83.7/12(.0), H = 16.3/1(.0)

1 M2 converting (C : H 6.975 : 16.3) to 3 : 7

1 M3 empirical formula = C3H7

1 M4 molecular formula = C6H14

1

M1 & M2 are for working M3 for C3H7 only, marked independently M4 for C6H14 only, marked independently (ignore additional correct structures) Formulae with no working cannot score M1 or M2

Alternative method: M1 working that shows 83.7% of 86 is 72 M2 idea of 72/12 gives 6 C atoms

Alternative method: working that shows that C6H14 (or C3H7) contains 83.7% C scores M1 & M2

[9]

Q9. (a) M1 Amount NaOH = 0.02530 × 0.500 = 0.01265 mol

567‑590 = 4 marks 0.567‑0.590 = 3 marks

1 M2 Amount acid = 0.006325 mol (i.e. M1 ÷ 2)

Allow ECF at each stage 1

M3 Mr = 90(.0) M3 can be scored from use of value of 90(.0) within working

1 M4 mass acid = 569 (mg) (allow 567 to 576) (i.e. M2 × M3 in mg)

M4 should be to at least 2sf. Any individual marks for M1/2/3 should be to at least 2sf (or 90 for M3)

1

1134‑1180 = 3 marks (due to not dividing moles of NaOH by 2) 1.134‑1.180 = 2 marks (due to not dividing moles of NaOH by 2 and not converting to mg)

(b) Idea that it ensures all ethanedioic acid / acid / sodium hydroxide / alkali / reactants are in the mixture / solution / reaction or the idea that some of the ethanedioic acid / acid / sodium hydroxide / alkali / reactants would be on the sides of the flask

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the idea that it is the transfer of all the acid/alkali alone is not enough

1

(c) Titres that are within 0.1 cm3 of each other Units are needed Allow 0.05‑0.15 cm3

Do not allow idea of identical results Allow answers that refer to titres that are within the uncertainty of the burette/apparatus of each other

1 [6]

Q10. C

[1]

Q11. B

[1]

Q12. C

[1]

Q13. B

[1]

Q14. B

[1]

Q15. B

[1]

Q16. B

[1]

Q17. B

[1]

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Q18. (a) Stage 1: appreciation that the acid must be in excess and calculation of amount of

solid that permits this

Statement that there must be an excess of acid 1

Moles of acid = 50.0 × 0.200 / 1000 = 1.00 × 10–2 mol 1

2 mol of acid react with 1 mol of calcium hydroxide therefore moles of solid weighed out must be less than half the moles of acid = 0.5 × 1.00 × 10–2 = 5.00 × 10–3 mol

1

Mass of solid must be –3 × 74.1 = 1

Stage 2: Experimental method

Measure out 50 cm3 of acid using a pipette and add the weighed amount of solid in a conical flask

1

Titrate against 0.100 (or 0.200) mol dm–3 NaOH added from a burette and record the volume (v) when an added indicator changes colour

1

Stage 3: How to calculate Mr from the experimental data

Moles of calcium hydroxide = 5.00 × 10–3 – (v/2 × conc NaOH) / 1000 = z mol 1

Mr = mass of solid / z 1

Extended response Maximum of 7 marks for answers which do not show a sustained line of reasoning which is coherent, relevant, substantiated and logically structured.

(b) Moles of calcium chloride = 3.56 / 111.1 = 3.204 × 10–2

1

Moles of calcium sulfate = 3.204 × 10–2 × 83.4 / 100 = 2.672 × 10–2

1

Mass of calcium sulfate = 2.672 × 10–2 × 136.2 = 3.6398 = 3.64 (g) Answer must be to 3 significant figures

1 [11]

Q19. B

[1]

Q20. B

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[1]

Q21. C

[1]

Q22. D

[1]

Q23. B

[1]

Q24. D

[1]

Q25. C

[1]

Q26. (a) Mass of X = 0.270

Volume of X = 105.0 Both must be correct

1

(b) pV = nRT

1

n = 3.41 × 10−3

1

Mr = or 1

Mr = 79.1 1

Identity of X = CH2Cl2

If Mr = 52 used, allow CH3Cl 1

(c) M1 The volume of the gas in the syringe (V) is greater than the true volume (because

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some air leaked into the syringe) If the Mr value of 52 is used and CH3Cl is identified in 01.2:

1

M2 Mr = m/n = m × RT/PV so if V is too large, Mr is too small

OR

M1 The temperature measured (T) is less than the temperature of the gas in the syringe (because the syringe heated faster than the oven and the oven temperature was not constant)

M2 Mr = m/n = m × RT/PV so if T is too small, Mr is too small

OR

M1 The measured mass of liquid transferred to the syringe (m) is less than the actual mass transferred

M2 Mr = m/n = m × RT/PV so if m is too small, Mr is too small M1 The volume of the gas in the syringe (V) is less than the true volume (because not all the liquid vaporised in the syringe) M2 Mr = m/n = m × RT/PV so if V is too small, Mr is too large OR M1 The temperature measured (T) is greater than the temperature of the gas in the syringe (because the syringe heated more slowly than the thermometer and the oven temperature was not constant) M2 Mr = m/n = m × RT/PV so if T is too large, Mr is too large OR M1 The measured mass of liquid transferred to the syringe (m) is greater than the actual mass transferred M2 Mr = m/n = m × RT/PV so if m is too large, Mr is too large

1

(d) Carry out in a fume cupboard Do not allow safety glasses / labcoat

1

To avoid toxic vapour 1

[10]

Q27. C

[1]

Q28. C

[1]

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Q29. B

[1]

Q30. B

[1]

Q31. A

[1]

Q32. D

[1]

Q33. C

[1]

Q34. (a) 4CuFeS2 + 9 O2 + 4SiO2 ⟶ Cu2S + Cu2O + 7SO2 + 4FeSiO3

Allow multiples 1

Cu2S + 2Cu2O ⟶ 6Cu + SO2 1

(b) ANY TWO • Prevents acid rain (which damages buidlings / ecology) • Toxic OR causes breathing problems • Reduces waste product OR makes use of the waste OR improves atom

economy OR Reduces need for sulfur mining OR used to produce sulfuric acid OR any named products

2

(c) M1, M2, M3 are process marks

M1 Mol Cu = (= 63780) 1

M2 Mass CuFeS2 = (63780) × 183.5 (= 1.17 × 107g) 1

M3 Mass ore = (1.17 × 107) × 1

M4 Mass ore = 936 tonnes (Allow 936 –937) 1

Alternative method M1 % of Cu in CuFeS2 = (63.5/183.5) × 100 = 34.6% M2 % of Cu in the rock = (34.6/100) × 1.25 = 0.4325% M3 mass of rock = 4050 × 100/0.4325 = 936416kg

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M4 mass of rock in tonnes = 936 tonnes

Notes M1 Ar Cu must be used M2 Mr CuFeS2 to have been used M3 Grossing up for the mass of rock M4 Final answer correct in tonnes

(d) % atom economy = × 100 1

= 74.3% must be 3sf 1

[10]

Q35. (a) Cl− 1s22s22p63s23p6

1 Fe2+1s22s22p63s23p63d6

1

If [Ne] or [Ar] used then Max 1if both correct Ignore 4s0

Allow subscripts

(b) Mn2+ (g) ⟶ Mn3+ (g) + e−

1

States symbols are required Allow Mn2+ (g) − e− ⟶ Mn3+ (g) Negative charge needed on electron

(c) Al Mg then CE = 0

1 (Outer) electron in (3)p sublevel / orbital

Not just level or shell 1

Higher in energy / further from the nucleus so easier to remove OWTTE

Both required for M3 1

Ignore shielding

(d) 58Ni+

M1 needs mass and charge – allow subscripts 1

Ar= [(58 × 61.0) + (60 × 29.1) + (61 × 9.9)] / 100 1

Ar= 58.9 must be to 1dp 1

[9]

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Amount of substance exam pack 2 new spec

Name: ________________________

Class: ________________________

Date: ________________________

Time: 208 minutes

Marks: 158 marks

Comments:

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Q1. Compounds containing Cu2+, OH– and CO32− ions are sometimes described as basic copper carbonates.

(a) Solid Cu2(OH)2CO3 is added to an excess of dilute hydrochloric acid. A solution of copper(II) chloride is formed, together with two other products.

(i) Write an equation for the reaction.

______________________________________________________________ (2)

(ii) Suggest one observation that could be made during the reaction.

______________________________________________________________

______________________________________________________________ (1)

(b) A 5.000 g sample of a different basic copper carbonate contains 0.348 g of carbon, 0.029 g of hydrogen and 1.858 g of oxygen.

(i) State what is meant by the term empirical formula.

______________________________________________________________

______________________________________________________________ (1)

(ii) Calculate the empirical formula of this basic copper carbonate. Show your working.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(Total 7 marks)

Q2. When heated, iron(III) nitrate (Mr = 241.8) is converted into iron(III) oxide, nitrogen dioxide and oxygen.

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4Fe(NO3)3(s) 2Fe2O3(s) + 12NO2(g) + 3O2(g)

A 2.16 g sample of iron(III) nitrate was completely converted into the products shown.

(a) (i) Calculate the amount, in moles, of iron(III) nitrate in the 2.16 g sample. Give your answer to 3 significant figures.

______________________________________________________________

______________________________________________________________ (1)

(ii) Calculate the amount, in moles, of oxygen gas produced in this reaction.

______________________________________________________________

______________________________________________________________ (1)

(iii) Calculate the volume, in m3, of nitrogen dioxide gas at 293 °C and 100 kPa produced from 2.16 g of iron(III) nitrate. The gas constant is R = 8.31 JK–1 mol–1.

(If you have been unable to obtain an answer to part (i), you may assume the number of moles of iron(III) nitrate is 0.00642. This is not the correct answer.)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (4)

(b) Suggest a name for this type of reaction that iron(III) nitrate undergoes.

___________________________________________________________________ (1)

(c) Suggest why the iron(III) oxide obtained is pure. Assume a complete reaction.

___________________________________________________________________

___________________________________________________________________

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(1) (Total 8 marks)

Q3. Some airbags in cars contain sodium azide (NaN3).

(a) Sodium azide is made by reacting dinitrogen monoxide gas with sodium amide (NaNH2) as shown by the equation.

2NaNH2 + N2O NaN3 + NaOH + NH3

Calculate the mass of sodium amide needed to obtain 550 g of sodium azide, assuming there is a 95.0% yield of sodium azide. Give your answer to 3 significant figures.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (5)

(b) If a car is involved in a serious collision, the sodium azide decomposes to form sodium and nitrogen as shown in the equation.

2NaN3(s) 2Na(s) + 3N2(g)

The nitrogen produced then inflates the airbag to a volume of 7.50 × 10−2 m3 at a pressure of 150 kPa and temperature of 35 °C.

Calculate the minimum mass of sodium azide that must decompose. (The gas constant R = 8.31 J K−1 mol−1)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (6)

(c) Sodium azide is toxic. It can be destroyed by reaction with an acidified solution of nitrous acid (HNO2) as shown in the equation.

2NaN3 + 2HNO2 + 2HCl 3N2 + 2NO + 2NaCl + 2H2O

(i) A 500 cm3 volume of the nitrous acid solution was used to destroy completely 150 g of the sodium azide.

Calculate the concentration, in mol dm−3, of the nitrous acid used.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Nitrous acid decomposes on heating.

Balance the following equation for this reaction.

........HNO2 .......HNO3 + .......NO + .......H2O (1)

(d) Sodium azide has a high melting point.

Predict the type of bonding in a crystal of sodium azide. Suggest why its melting point is high.

Type of bonding _____________________________________________________

Reason for high melting point ___________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(e) The azide ion has the formula N3−

(i) The azide ion can be represented as N N − N−

One of these bonds is a co−ordinate bond.

On the following diagram, draw an arrowhead on one of the bonds to represent

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the direction of donation of the lone pair in the co−ordinate bond.

N N − N− (1)

(ii) Give the formula of a molecule that has the same number of electrons as the azide ion.

______________________________________________________________ (1)

(iii) Which is the correct formula of magnesium azide?

Tick (✓) one box.

Mg3N

MgN

MgN6

Mg3N2


Q4. N-phenylethanamide is used as an inhibitor in hydrogen peroxide decomposition and also in the production of dyes.

N-phenylethanamide can be produced in a laboratory by the reaction between phenylammonium sulfate and an excess of ethanoic anhydride:

(a) A student carried out this preparation using 1.15 g of phenylammonium sulfate (Mr = 284.1) and excess ethanoic anhydride.

(i) Calculate the maximum theoretical yield of N−phenylethanamide that could be produced in the reaction. Record your answer to an appropriate precision.

Show your working.

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(ii) In the preparation, the student produced 0.89 g of N−phenylethanamide.

Calculate the percentage yield for the reaction.

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______________________________________________________________ (1)

(b) The student purified the crude solid product, N−phenylethanamide, by recrystallisation.

(i) Outline the method that the student should use for this recrystallisation.

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(ii) Outline how you would carry out a simple laboratory process to show that the recrystallised product is a pure sample of N−phenylethanamide.

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(iii) Assume that the reaction goes to completion.

Suggest two practical reasons why the percentage yield for this reaction may not be 100%.

1. ____________________________________________________________

______________________________________________________________

2. ____________________________________________________________

______________________________________________________________ (2)

(c) The reaction to form N−phenylethanamide would happen much more quickly if the student used ethanoyl chloride instead of ethanoic anhydride.

Explain why the student might prefer to use ethanoic anhydride, even though it has a slower rate of reaction.

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___________________________________________________________________ (2)

(Total 15 marks)

Q5. In a titration experiment, a good technique is essential for an accurate result to be obtained.

(a) Suggest a reason for removing the funnel after it has been used for filling the burette.

___________________________________________________________________

___________________________________________________________________ (1)

(b) Suggest one other source of error in using the burette to carry out a titration.

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___________________________________________________________________ (1)

(c) During the titration, the inside of the conical flask is rinsed with distilled water.

Suggest why rinsing improves the accuracy of the titre.

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___________________________________________________________________ (1)

(d) Explain why adding this extra water does not change the volume of EDTA solution that is required in the titration.

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(Total 4 marks)

Q6. When boric acid (H3BO3) is applied as a coating on wood, it acts as a fire retardant by decreasing the rate of combustion.

Thermal decomposition of boric acid takes place in two stages.

In an experiment a sample of boric acid was heated in a crucible at 170 °C. The results of this experiment are given in the table.

Time of heating / minutes Mass of crucible and contents / g

0 35.85

5 35.10

10 34.41

15 34.00

20 33.70

25 33.56

30 33.50

35 33.50

Plot a graph of the results from the table above to show the mass of the crucible and boric acid (y-axis) against time of heating on the grid.

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(Total 4 marks)

Q7. (a) Suggest one reason why sugars are often added to antacid tablets.

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___________________________________________________________________ (1)

(b) In one titration, a student added significantly more phenolphthalein than instructed. The volume of sodium hydroxide solution in this titration was greater than the average value of the concordant titres.

State a property of the indicator that would explain this result.

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___________________________________________________________________ (1)

(c) Some other types of antacid tablets contain carbonate ions.

Suggest why this may be a disadvantage when used as a medicine to relieve indigestion.

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(Total 3 marks)

Q8. A sample of hydrated nickel sulfate (NiSO4.xH2O) with a mass of 2.287 g was heated to remove all water of crystallisation. The solid remaining had a mass of 1.344 g.

(a) Calculate the value of the integer x. Show your working.

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(b) Suggest how a student doing this experiment could check that all the water had been removed.

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(Total 6 marks)

Q9. Phosphoric(V) acid (H3PO4) is an important chemical. It can be made by two methods. The first method is a two-step process.

(a) In the first step of the first method, phosphorus is burned in air at 500 ºC to produce gaseous phosphorus(V) oxide.

P4(s) + 5O2(g) → P4O10(g)

220 g of phosphorus were reacted with an excess of air.

Calculate the volume, in m3, of gaseous phosphorus(V) oxide produced at a pressure of 101 kPa and a temperature of 500 ºC. The gas constant R = 8.31 J K–1 mol–1

Give your answer to 3 significant figures.

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(b) In the second step of the first method, phosphorus(V) oxide reacts with water to form phosphoric(V) acid.

P4O10(s) + 6H2O(l) → 4H3PO4(aq)

Calculate the mass of phosphorus(V) oxide required to produce 3.00 m3 of 5.00 mol dm–3 phosphoric(V) acid solution.

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(c) In the second method to produce phosphoric(V) acid, 3.50 kg of Ca3(PO4)2 are added to an excess of aqueous sulfuric acid.

Ca3(PO4)2(s) + 3H2SO4(aq) → 2H3PO4(aq) + 3CaSO4(s)

1.09 kg of phosphoric(V) acid are produced.

Calculate the percentage yield of phosphoric(V) acid.

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(d) Explain whether the first method or the second method of production of phosphoric acid has the higher atom economy. You are not required to do a calculation.

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(Total 12 marks)

Q10. Glucose can decompose in the presence of microorganisms to form a range of products. One of these is a carboxylic acid (Mr = 88.0) containing 40.9% carbon and 4.5% hydrogen by mass.

(a) Deduce the empirical and molecular formulas of the carboxylic acid formed.

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Empirical formula = ___________ Molecular formula = ___________ (4)

(b) Ethanol is formed by the fermentation of glucose. A student carried out this fermentation reaction in a beaker using an aqueous solution of glucose at a temperature of 25 °C in the presence of yeast.

Write an equation for the reaction occurring during fermentation.

___________________________________________________________________ (1)

(c) In industry, this fermentation reaction is carried out at 35 °C rather than 25 °C.

Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature.

Advantage __________________________________________________________

___________________________________________________________________

Disadvantage _______________________________________________________

___________________________________________________________________ (2)

(d) The method used by the student in part (b) would result in the ethanol being contaminated by ethanoic acid.

How does this contamination occur?

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___________________________________________________________________ (1)

(e) Give two differences between the infrared spectrum of a carboxylic acid and that of an alcohol other than in their fingerprint regions. Use Table A on the Data Sheet.

Difference 1 ________________________________________________________

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Difference 2 _________________________________________________________

___________________________________________________________________ (2)

(Total 10 marks)

Q11. The Mr of hydrated copper sulfate (CuSO4.5H2O) is 249.6.

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Which of the following is the mass of hydrated copper sulfate required to make 50.0 cm3 of a 0.400 mol dm−3 solution?

A 3.19 g

B 3.55 g

C 3.71 g


Q12. 30 cm3 of xenon are mixed with 20 cm3 of fluorine. The gases react according to the following equation. Assume that the temperature and pressure remain constant.

Xe(g) + F2(g) → XeF2(g)

What is the final volume of gas after the reaction is complete?

A 50 cm3

B 40 cm3

C 30 cm3

D 20 cm3

(Total 1 mark)

Q13. In a car airbag, sodium azide (NaN3) decomposes to form sodium metal and nitrogen gas.

2NaN3(s) → 2Na(s) + 3N2(g)

The sodium metal then reacts with potassium nitrate to produce more nitrogen gas.

10Na(s) + 2KNO3(s) → N2(g) + 5Na2O(s) + K2O(s)

If 2.00 mol of sodium azide react in this way, how many molecules of N2 will be formed? (The Avogadro constant L = 6.022 × 1023 mol–1)

A 2.41 × 1024

B 1.93 × 1024

C 1.81 × 1024

D 9.63 × 1023

(Total 1 mark)

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Q14. Which of the following solutions would react exactly with a solution containing 0.0500 mol sulfuric acid?

A 50.0 cm3 of 1.00 mol dm−3 KOH

B 100.0 cm3 of 2.00 mol dm−3 KOH

C 100.0 cm3 of 2.00 mol dm−3 Ba(OH)2

D 50.0 cm3 of 1.00 mol dm−3 Ba(OH)2

(Total 1 mark)

Q15. The diagram represents two glass flasks, P and Q, connected via a tap.

Flask Q (volume = 1.00 × 103 cm3) is filled with ammonia (NH3) at 102 kPa and 300 K. The tap is closed and there is a vacuum in flask P. (Gas constant R = 8.31 J K−1 mol−1)

(a) Calculate the mass of ammonia in flask Q. Give your answer to the appropriate number of significant figures.

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(b) When the tap is opened, ammonia passes into flask P. The temperature decreases by 5 °C. The final pressure in both flasks is 75.0 kPa. Calculate the volume, in cm3, of flask P.

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(Total 6 marks)

Q16.

In a molecule of a hydrocarbon, the fraction by mass of carbon is

What is the empirical formula of the hydrocarbon?

A CH

B CH3

C C3H8

D C5H12

(Total 1 mark)

Q17. Refer to the unbalanced equation below when answering this question.

K2Cr2O7 + 3H2C2O4 + _H2SO4 → Cr2(SO4)3 + _H2O + 6CO2 + K2SO4

In the balanced equation the mole ratio for sulfuric acid to water is

A 1 : 4

B 1 : 2

C 4 : 7

D 4 : 9 (Total 1 mark)

Q18. There are 392 mol of pure gold in a bar measuring 10 cm by 10 cm by 40 cm. What is the density of gold in kg dm−3?

A 193

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B 19.3

C 1.93


Q19. This question is about a white solid, MHCO3, that dissolves in water and reacts with hydrochloric acid to give a salt.

MHCO3 + HCl → MCl + H2O + CO2

A student was asked to design an experiment to determine a value for the Mr of MHCO3. The student dissolved 1464 mg of MHCO3 in water and made the solution up to 250 cm3. 25.0 cm3 samples of the solution were titrated with 0.102 mol dm−3 hydrochloric acid. The results are shown in the table.

Rough 1 2 3

Initial burette reading / cm3 0.00 10.00 19.50 29.25

Final burette reading / cm3 10.00 19.50 29.25 38.90

Titre / cm3 10.00 9.50 9.75 9.65

(a) Calculate the mean titre and use this to determine the amount, in moles, of HCl that reacted with 25.0 cm3 of the MHCO3 solution.

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(b) Calculate the amount, in moles, of MHCO3 in 250 cm3 of the solution. Then calculate the experimental value for the Mr of MHCO3. Give your answer to the appropriate number of significant figures.

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___________________________________________________________________ (3)

(c) The student identified use of the burette as the largest source of uncertainty in the

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experiment.

Using the same apparatus, suggest how the procedure could be improved to reduce the percentage uncertainty in using the burette.

Justify your suggested improvement.

Suggestion _________________________________________________________

___________________________________________________________________

Justification _________________________________________________________

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___________________________________________________________________ (2)

(d) Another student is required to make up 250 cm3 of an aqueous solution that contains a known mass of MHCO3. The student is provided with a sample bottle containing the MHCO3.

Describe the method, including apparatus and practical details, that the student should use to prepare the solution.

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(Total 14 marks)

Q20. Two reactions occurred when the impure quicklime was added to the acid. Calcium oxide reacted according to this equation

CaO(s) + 2HCl(aq) → CaCl2(aq) + H2O(l)

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Some carbon dioxide was evolved by the reaction of any remaining calcium carbonate that had not decomposed in the kiln.

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

The carbon dioxide was collected and its volume was found to be 18.3 dm3 at a temperature of 25 ºC and pressure of 100 kPa. The gas constant R = 8.31 J K–1 mol–1

(a) Calculate the amount, in moles, of carbon dioxide that was given off when the impure quicklime reacted with the hydrochloric acid. Show your working.

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___________________________________________________________________ (2)

(b) Calculate the amount, in moles, of hydrochloric acid used up by the reaction with calcium carbonate. Show your working.

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___________________________________________________________________ (1)

(c) Use your Periodic Table to calculate the relative formula mass of CaCO3


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(d) Use your answers to part (a) and part (c) to calculate the mass of calcium carbonate in the sample of quicklime.

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(Total 5 marks)

Q21. The oxidising agent in solution A is sodium bromate(V), NaBrO3. A laboratory technician wanted to make up enough of this solution for use in a class practical.

Calculate the mass of sodium bromate(V) needed to prepare 5.00 dm3 of a 5.00 × 10–

3 mol dm–3 solution.

Show your working. Give your answer to the appropriate precision.

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_______________________________________________________________________ (Total 2 marks)

Q22. A different kind of kiln is used to manufacture Portland cement. The main active minerals in Portland cement are called alite and belite.

(a) The table shows the composition of a compound found in alite that contains only the elements calcium, silicon and oxygen. Use these percentage by mass data to determine the empirical formula of this compound.

Ca Si O

% by mass 52.67 12.30 To be calculated

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(b) A compound (Ca2SiO4) in belite reacts with water to produce Ca3Si2O4(OH)6 and Ca(OH)2

Write an equation for this reaction.

___________________________________________________________________ (1)

(c) Bags of Portland cement are labelled with hazard warnings. Suggest an item of personal safety equipment, other than eye protection, that the warning label recommends. Give a reason why this safety equipment is recommended.

Safety equipment __________________________________________________

Reason __________________________________________________________ (2)

(Total 6 marks)

Q23. The following equation represents the oxidation of vanadium(IV) ions by manganate(VII) ions in acid solution.

5V4+ + MnO4– + 8H+ 5V5+ + Mn2+ + 4H2O

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What volume of 0.020 mol dm–3 KMnO4 solution is required to oxidise completely a solution containing 0.010 mol of vanadium(IV) ions?

A 10 cm3

B 25 cm3

C 50 cm3

D 100 cm3 (Total 1 mark)

Q24. A saturated aqueous solution of magnesium hydroxide contains 1.17 × 10–3 g of Mg(OH)2 in 100 cm3 of solution. In this solution, the magnesium hydroxide is fully dissociated into ions.

What is the concentration of Mg2+(aq) ions in this solution?

A 2.82 × 10–2 mol dm–3

B 2.01 × 10–3 mol dm–3

C 2.82 × 10–3 mol dm–3

D 2.01 × 10–4 mol dm–3 (Total 1 mark)

Q25. In an experiment to identify a Group 2 metal (X), 0.102 g of X reacts with an excess of aqueous hydrochloric acid according to the following equation.

X + 2HCl XCl2 + H2

The volume of hydrogen gas given off is 65 cm3 at 99 kPa pressure and 303 K. The gas constant is R = 8.31 J K–1 mol–1.

Which is X?

A Barium

B Calcium

C Magnesium

D Strontium (Total 1 mark)

Q26. Magnesium reacts with hydrochloric acid according to the following equation.

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Mg + 2HCl MgCl2 + H2

A student calculated the minimum volume of 2.56 mol dm–3 hydrochloric acid required to react with an excess of magnesium to form 5.46 g of magnesium chloride (Mr = 95.3).

Which of the following uses the correct standard form and the appropriate number of significant figures to give the correct result of the calculation?

A 4.476 × 10–2 dm3

B 4.48 × 10–2 dm3

C 4.50 × 10–2 dm3

D 44.8 × 10–3 dm3 (Total 1 mark)

Q27. Which of these samples of gas contains the largest number of molecules? The gas constant R = 8.31 J K–1 mol–1.

A 5.0 × 10–4 m3 at 1.0 × 106 Pa and 300 K

B 4.0 × 10–3 m3 at 2.0 × 105 Pa and 400 K

C 3.0 × 101 dm3 at 3.0 × 104 Pa and 500 K

D 2.0 × 102 dm3 at 4.0 × 103 Pa and 600 K (Total 1 mark)

Q28. A sample of 2.18 g of oxygen gas has a volume of 1870 cm3 at a pressure of 101 kPa.

What is the temperature of the gas? The gas constant is R = 8.31 J K–1 mol–1.

A 167 K

B 334 K

C 668 K

D 334 000 K (Total 1 mark)

Q29. An ester is hydrolysed as shown by the following equation.

RCOOR/ + H2O RCOOH + R/OH

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What is the percentage yield of RCOOH when 0.50 g of RCOOH (Mr = 100) is obtained from 1.0 g of RCOOR/ (Mr = 150)?

A 33%

B 50%

C 67%

D 75% (Total 1 mark)

Q30. What is the total volume of gas remaining after 20 cm3 ethane are burned completely in 100 cm3 oxygen? All volumes are measured at the same pressure and the same temperature, which is above 100 °C.

C2H6 + 3 O2 2CO2 + 3H2O

A 40 cm3

B 100 cm3

C 120 cm3

D 130 cm3

(Total 1 mark)

Q31. This question is about reactions of calcium compounds.

(a) A pure solid is thought to be calcium hydroxide. The solid can be identified from its relative formula mass.

The relative formula mass can be determined experimentally by reacting a measured mass of the pure solid with an excess of hydrochloric acid. The equation for this reaction is

Ca(OH)2 + 2HCl CaCl2 + 2H2O

The unreacted acid can then be determined by titration with a standard sodium hydroxide solution.

You are provided with 50.0 cm3 of 0.200 mol dm−3 hydrochloric acid. Outline, giving brief practical details, how you would conduct an experiment to calculate accurately the relative formula mass of the solid using this method.

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(b) A 3.56 g sample of calcium chloride was dissolved in water and reacted with an excess of sulfuric acid to form a precipitate of calcium sulfate.

The percentage yield of calcium sulfate was 83.4%.

Calculate the mass of calcium sulfate formed. Give your answer to an appropriate number of significant figures.

Mass of calcium sulfate formed = ____________ g (3)

(Total 11 marks)

Q32. Which of the following contains the most chloride ions?

A 10 cm3 of 3.30 × 10−2 mol dm−3 aluminium chloride solution

B 20 cm3 of 5.00 × 10−2 mol dm−3 calcium chloride solution

C 30 cm3 of 3.30 × 10−2 mol dm−3 hydrochloric acid

D 40 cm3 of 2.50 × 10−2 mol dm−3 sodium chloride solution (Total 1 mark)

Q33. A student is provided with a 5.00 cm3 sample of 1.00 × 10−2 mol dm−3 hydrochloric acid. The student is asked to devise a method to prepare a hydrochloric acid solution with a concentration of 5.00 × 10−4 mol dm−3 by diluting the sample with water.

Which of these is the correct volume of water that should be added?

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A 45.0 cm3

B 95.0 cm3

C 100 cm3

D 995 cm3

(Total 1 mark)

Q34. Which of these pieces of apparatus has the lowest percentage uncertainty in the measurement shown?

A Volume of 25 cm3 measured with a burette with an uncertainty of ±0.1 cm3.

B Volume of 25 cm3 measured with a measuring cylinder with an uncertainty of ±0.5 cm3.

C Mass of 0.150 g measured with a balance with an uncertainty of ±0.001 g.

D Temperature change of 23.2 °C measured with a thermometer with an uncertainty of ±0.1 °C.

(Total 1 mark)

Q35. A sample of pure Mg(NO3)2 was decomposed by heating as shown in the equation below.

2Mg(NO3)2(s) 2MgO(s) + 4NO2(g) + O2(g)

(a) A 3.74 × 10−2 g sample of Mg(NO3)2 was completely decomposed by heating.

Calculate the total volume, in cm3, of gas produced at 60.0 °C and 100 kPa. Give your answer to the appropriate number of significant figures. The gas constant R = 8.31 J K−1 mol−1.

Total volume of gas = ___________ cm3

(5)

(b) The mass of MgO obtained in this experiment is slightly less than that expected from the mass of Mg(NO3)2 used. Suggest one practical reason for this.

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___________________________________________________________________ (1)

(Total 6 marks)

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Mark schemes

Q1. (a) (i) H2O + CO2 (as products in any equation)

Allow H2O + H2CO3 1

Cu2(OH)2CO3 + 4HCl → 2CuCl2 + 3H2O + CO2

Allow multiples Ignore states

1

(ii) Bubbles or fizzing or effervescence Or solid disappears Or blue(-green) solution

Do not allow dissolves Ignore CO2 gas or gas evolved

1

(b) (i) Simplest (whole-number) ratio of atoms of each element in a compound Allow atoms of Cu, H & O in this compound

1

(ii) Mass of copper = 2.765 Dividing masses by Ar

1

1

Correct whole number ratio of integers or Cu:C:H:O 3:2:2:8 or Correct empirical formula Cu3C2H2O8

Any order Ignore Cu3(OH)2(CO3)2

1 [7]

Q2. (a) (i) 2.16 ÷ 241.8 = 0.00893 or 8.93 × 10−3 (mol)

Penalise if not 3 significant figures. 1

(ii) n(O2) = 0.00893 × 0.75 (= 0.00670 mol) Allow part(i) × 0.75 .

1

(iii) M1 = T = 566 K and P = 100 000 Pa If M1 incorrect can only score M2 and M3.

1

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M2 = Moles NO2 = 0.0268 (mol) If M2 incorrect can only score M1 and M3. Allow moles of NO2 = student’s answer to part (i) × 3. OR part (ii) × 4 and consequential M4. Minimum of 2 significant figures.

1

M3 = V = OR =

If M3 incorrect can only score M1 and M2. 1

M4 = 0.00126 (m3) or 1.26 × 10−3 (m3) Allow minimum of 2 significant figures. Allow no units but incorrect units loses M4. If 0.00642 moles used: M2 = Moles NO2 = 0.0193 mol.

M3 = V = = . M4 = 9.06 × 10−4 (m3) allow 9.06 to 9.08 × 10−4.

1

(b) (Thermal) decomposition Do not allow catalytic decomposition.

1

(c) Other products are gases / other products escape easily Allow no other solid (or liquid) product.

1 [8]

Q3.

(a) M1 550 × = 579 g would be 100% mass Allow alternative methods. There are 4 process marks:

1

M2 So = 8.91 moles NaN3

or

M1 = 8.46 moles NaN3 (this is 95%)

M2 So 100% would be 8.46 × = 8.91 moles NaN3

1: mass ÷ 65 2: mass or moles × 100 / 95 or × 1.05 3: moles NaN3 × 2

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4: moles NaNH2 × 39 1

Then M3 Moles NaNH2 = 8.91 × 2 = ( 17.8(2) moles) 1

M4 mass NaNH2 = 17.8(2) × 39 1

M5 693 or 694 or 695 (g) If 693, 694 or 695 seen to 3 sig figs award 5 marks

1

(b) M1 308 K and 150 000 Pa 1

M2 n = or 1

M3 = 4.4(0) or 4.395 moles N2

Allow only this answer but allow to more than 3 sig figs 1

M4 Moles NaN3 = 4.395 × (= 2.93)

M4 is for M3 × 1

M5 Mass NaN3 = (2.93) × 65 M5 is for moles M4 × 65

1

M6 = 191 g Allow 190 to 191 g allow answers to 2 sig figs or more

1

(c) (i) 150 / 65 = 2.31 moles NaN3 or 2.31 moles nitrous acid 1

Conc = 2.31 × M2 is for M1 × 1000 / 500

1

4.6(1) or 4.6(2) (mol dm−3) Only this answer

1

(ii) 3HNO2 HNO3 + 2NO + H2O

Can allow multiples 1

(d) Ionic If not ionic then CE = 0 / 3

1

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Oppositely charged ions / Na+ and N3 − ions Penalise incorrect ions here but can allow M3

1

Strong attraction between (oppositely charged) ions / lots of energy needed to overcome (strong) attractions (between ions)

M3 dependent on M2 1

(e) (i) N ≡ N N−

Only 1

(ii) CO2 / N2O / BeF2 / HN3

Allow other correct molecules 1

(iii) MgN6

Only 1

[21]

Q4. (a) (i) Mr N−phenylethanamide = 135.0

1

Theoretical yield = 135.0 × 2 (1.15 / 284.1) = 1.09 g 1

Answer recorded to 3 significant figures. 1

(ii) × 100

= 81.4 % Mark consequentially to (a) Allow 81 to 82

1

(b) (i) Dissolve the product in the minimum volume of water / solvent (in a boiling tube / beaker)

If dissolving is not mentioned, CE = 0 / 4 1

Hot water / solvent Steps must be in a logical order to score all 4 marks

1

Allow the solution to cool and allow crystals to form. 1

Filter off the pure product under reduced pressure / using a Buchner funnel and side arm flask

Ignore source of vacuum for filtration (electric pump, water pump, etc.)

1

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(ii) Measure the melting point 1

Use of melting point apparatus or oil bath 1

Sharp melting point / melting point matches data source value 1

(iii) Any two from: Product left in the beaker or glassware Sample was still wet Sample lost during recrystallisation.

Do not allow “sample lost” without clarification. 2 Max

(c) An identified hazard of ethanoyl chloride E.g. “Violent reaction”, “harmful”, “reacts violently with water” Do not allow “toxic”, “irritant” (unless linked with HCl gas).

1

HCl gas / fumes released / HCl not released when ethanoic anhydride used 1

[15]

Q5. (a) As a droplet from the funnel could enter the burette / affect volume / readings / titre

1

(b) Air bubble in jet or wtte Do not allow misreading burette or overshooting end point.

1

(c) Ensures all reagents are able to react / mix / come into contact Accept no reagent is left unreacted on sides of flask Do not allow any reference to ‘removal’ of the solution unless it is clear that it is added to the flask.

1

(d) The added water does not affect the mols / amount of reagents / reactants / solution Z

Do not allow mols of solution or mols in the flask. Allow water does not react with the reagents / water is not one of the reactants Do not allow ‘water is not involved’

1 [4]

Q6. Mass of crucible and boric acid on the y−axis

Axes must be labelled but do not penalise lack of units (unless incorrect).

1

Suitable scale used

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Plotted points must cover at least half the printed grid.(both directions).

1

All points plotted correctly Allow + / − one small square.

1

Suitable line drawn Good best−fit line based on their points (+ / − one small square). Do not award if kinked, doubled or very thick line.

1 [4]

Q7. (a) (To make chewing the tablets) more palatable

Tastes better / sweet taste / mask the taste of the Mg(OH)2

Do not allow ‘to aid digestion’. 1

(b) The indicator is acidic 1

(c) They produce CO2 gas that may produce ‘wind’ / a bloated feeling. 1

[3]

Q8. (a) 0.943 g water (M1)

If Mr of NiSO4 wrong, can allow M1 and M3 from method 1 i.e. max 2

NiSO4 H2O

(M2) (M3)

(8.68 × 10−3 0.052)

1 6 or x = 6 (M4) Allow Mr = 155

Allow other methods e.g.

Mr (NiSO4) = 58.7 + 32.1 + 64.0 = 154.8

n(NiSO4) = = 0.008682 mol (M1)

Mr (NiSO4.xH2O) = = (263.4) (M2)

so 18x = 263.4 − 154.8 = (108.6) (M3)

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so x = = 6 (M4) If using alternative method and Mr of NiSO4 wrong, allow ecf to score M2 and M3 only i.e. max 2

4

(b) re-heat Heat to constant mass = 2 marks

1

check that mass is unchanged M2 dependent on M1 Allow as alternative: M1: record an IR spectrum M2: peak between 3230 and 3550 (cm−1)

1 [6]

Q9. (a) Correct conversion of temperature and pressure (773 and 101 × 103)

Correct answer with or without working scores 4 marks 1

No moles P = (220 / 4 × 31.0) = 1.77 Max 2 (M1 and M3) if 31.0 used (=0.451 m3 or if 220/31 rounded to 2 sf ie 7.1 then 0.452)

1 V = nRT/P (correct rearrangement or insert of values V = 1.77 × 8.31 × 773/101 × 103 =0.1128 m3)

Max 2 (M1 and M3) if 284 (P4O10) used then 0.0493 1

V = 0.113 (m3) Must be 3 sig figs

1

(b) No moles H3PO4 = 3 × 103 (dm3) × 5 = 15,000 (mols) Correct answer with or without working scores 3 marks If M1 incorrect then can only score M2

1

No moles phosphorus(V) oxide = ( = 3,750 mols)

If M2 incorrect can only score M1

1 1.1 × 106 or1.07 × 106 or 1.065 × 106 (g) or 1,100 or 1,070 or 1065 kg or 1.1 or 1.07 or 1.065 tonne

= (3.75 × 103 × 284.0) Min 2 sig fig

1

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(c) No moles Ca3(PO4)2 (= 3.50kg =) = 11.28 Correct answer with or without working scores 4 marks If M1 incorrect can only score M2 and M3

1 Theoretical No. moles H3PO4 = 11.28 × 2 = 22.56

If M2 incorrect can only score M1 and M3 1

Theoretical mass H3PO4 = 22.56 × 98(.0) = 2211 If M3 incorrect can only score M1and M2

1

or Actual No. moles H3PO4 produced = = 11.12 49 – 49(.312) (%)

1

(d) Method 1 / (a) & (b) because only one product / no other products formed / atom economy = 100% (even though two steps)

Allow calculations Do not allow if P2O5 is formed Allow converse explanation

1 [12]

Q10. (a) Percentage of oxygen by mass = 100 – 40.9 – 4.5 = 54.6

1

C H O

% Divide by Ar

= 3.41 = 4.5 = 3.41 1

Divide by smallest =

Nearest whole number ratio = 1 × 3 1.32 × 3 1 × 3

= 3 : 3.96 : 3

Nearest integer ratio = 3 : 4 : 3 1

Empirical formula C3H4O3

Empirical formula mass = 88 = molecular formula mass

Therefore, molecular formula is same as the empirical formula - C3H4O3

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1

(b) C6H12O6 2C2H5OH + 2CO2 1

(c) Advantage – ethanol is produced at a faster rate 1

Disadvantage – more energy is used / required in the reaction 1

(d) Air gets in / oxidation occurs 1

(e) Alcohol OH absorption in different place (3230–3550 cm–1) from acid OH absorption (2500–3000 cm–1)

1

The C=O in acids has an absorption at 1680–1750 cm–1

1 [10]

Q11. D

[1]

Q12. C

[1]

Q13. B

[1]

Q14. D

[1]

Q15. (a) n = PV/RT

If PV=nRT rearranged incorrectly then M3 only 1

1

Mass = M2 × 17 = 0.696 (g) (3 sig figs only) Allow 0.695 or 0.697

1

(b) If pV = nRT

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Incorrect unit conversion loses M1 only; can get M2/M3 if possible volume obtained

= 1.34 × 10−3 m3

Inserts correct numbers (inc pressure in Pa) 1

Volume of Q in m3 = 1.00 × 10−3

Volume of bulb P = 1.34 × 10−3 – 1.00 × 10−3

Volume of bulb P = 3.42 × 10−4 m3

No subtraction M1 only 1

= 342 cm3 (Allow 310 − 342 cm3) Alternative method also worth full credit (note if mol in M2 of 05.1 rounded to 0.04 this could lead to a final answer of 3.1 × 10−4 m3 so allow range 310 − 342 cm3

1 [6]

Q16. C

[1]

Q17. C

[1]

Q18. B

[1]

Q19. (a) Selects correct titres

If 3 or more titres used them MAX 1 for conseq M3 1

= 9.7(0) cm3

Calculates mean 1

mol HCL = 0.102 × 9.70/1000 = 9.89 × 10−4

(allow 9.9 × 10-4 for M3 but check not via 4 titres in which case only 1 mark)

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Calculates mol (working or result gains credit) 9.92 × 10−4 scores 1 if all 4 titres used 9.83 × 10−4 scores 1 if titres 1,2, and 3 used

1

(b) mol MHCO3 = ANS 3.1 × 10 (= 9.89 × 10−3) Use ecf if wrong mean calculated above

1

1

Mr = 148 (3sf) Allow ecf following wrong mass conversion

1

(c) Suggestion: Use a larger mass of solid OR use a more concentrated solution of MHCO3 OR less concentrated / more dilute solution of HCl OR more MHCO3

1

Cannot score justification mark unless suggestion correct, but suggestion could be after justification

Justification: So a larger titre/reading will be needed OR larger volume of HCl Assume reference to the solution means the MHCO3

1

(d) This question is marked using levels of response.

Level 3 Must use volumetric flask to access level 3 Answer is communicated coherently and shows a logical progression from stage 1 to stage 2 then stage 3.

All stages are covered and the description of each stage is complete 6 marks

All stages are covered but up to 2 omissions/errors from different stages. If 2 omissions/errors from same stage only level 2 possible

5 marks

Level 2 Answer is mainly coherent and shows progression from stage 1 to stage 3

All stages are covered but 3 omissions/errors 4 marks

All stages are attempted 3 marks

Level 1 Answer includes isolated statements but these are not presented in a logical order or show confused reasoning.

2 stages attempted 2 marks

1 stage attempted 1 mark

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Level 0 Insufficient correct chemistry to gain a mark.

0 marks

Indicative Chemistry content Stage 1: transfers known mass of solid a) Weigh the sample bottle containing the solid on a (2 dp) balance b) Transfer to beaker* and reweigh sample bottle c) Record the difference in mass Or d) Place beaker* on balance and tare e) Transfer solid into beaker f) Record mass Or g) Known mass provided h) Transfers (known) mass into beaker* i) Wash all remaining solid from sample bottle into beaker Allow use of weighing boat *Allow other suitable glassware including volumetric flask Stage 2: Dissolves in water a) Add distilled / deionised water b) Stir (with a glass rod) or swirl c) Until all solid has dissolved Stage 3: Transfer, washing and agitation a) Transfer to volumetric / graduated flask. Allow if a clear description/diagram given eg long necked flask with 250 cm3 mark b) With washings c) Make up to 250 cm3 / mark with water d) Shakes/inverts/mixes

6 [14]

Q20. (a) n = pV/RT M1

Do not accept pV=nRT as the sole working. Allow correct substitution of numbers.

1

0.739 M2 Answer must be to a minimum of 2 s.f. Correct answer without working scores M2 only.

1

(b) (a) × 2 Answer will often be 1.48 (or 1.5 or 1.478) Answer must be to a minimum of 2 s.f.

1

(c) 100.1 Answer must be to 1 d.p.

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1

(d) (a) × (c) Answer will often be 74.0 Answer must be to a minimum of 2 s.f.

1 [5]

Q21. Mr of sodium bromate(V) = 150.9 and Mol sodium bromate(V) = 5.00 x (5.00 x 10–3) = 0.0250 M1

Lose M1 if 151 used (final answer may appear as 3.78). 1

Mass sodium bromate(V) = 0.025 x 150.9 = 3.77 g M2 Lose M2 if answer not to 3 sig figs. Correct answer without working scores M2 only.

1 [2]

Q22. (a) Percentage of oxygen 35.03 M1

Values used throughout must be to a minimum of 2 s.f. 1

52.67 / 40.1 12.3 / 28.1 35.03 / 16 M2 OR 1.313 0.438 2.189

If ratios are inverted lose M2 and M3 1

Ca3SiO5 M3 If correct formula only is given allow M3 only.

1

(b) 2 Ca2SiO4 + 4 H2O → Ca3Si2O4(OH)6 + Ca(OH)2

Accept multiples and fractions. Ignore state symbols. 1

(c) Gloves / Dust or face-mask Ignore references to use of fume cupboard.

1

Cement is alkaline / caustic / corrosive / irritant Accept ‘Ca(OH)2 formed is alkaline / caustic / corrosive / irritant’.

1 [6]

Q23. D

[1]

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Q24. D

[1]

Q25. B

[1]

Q26. B

[1]

Q27. B

[1]

Q28. B

[1]

Q29. D

[1]

Q30. D

[1]

Q31. (a) Stage 1: appreciation that the acid must be in excess and calculation of amount of

solid that permits this

Statement that there must be an excess of acid 1

Moles of acid = 50.0 × 0.200 / 1000 = 1.00 × 10–2 mol 1

2 mol of acid react with 1 mol of calcium hydroxide therefore moles of solid weighed out must be less than half the moles of acid = 0.5 × 1.00 × 10–2 = 5.00 × 10–3 mol

1

Mass of solid must be –3 × 74.1 = 1

Stage 2: Experimental method

Measure out 50 cm3 of acid using a pipette and add the weighed amount of solid

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in a conical flask 1

Titrate against 0.100 (or 0.200) mol dm–3 NaOH added from a burette and record the volume (v) when an added indicator changes colour

1

Stage 3: How to calculate Mr from the experimental data

Moles of calcium hydroxide = 5.00 × 10–3 – (v/2 × conc NaOH) / 1000 = z mol 1

Mr = mass of solid / z 1

Extended response Maximum of 7 marks for answers which do not show a sustained line of reasoning which is coherent, relevant, substantiated and logically structured.

(b) Moles of calcium chloride = 3.56 / 111.1 = 3.204 × 10–2

1

Moles of calcium sulfate = 3.204 × 10–2 × 83.4 / 100 = 2.672 × 10–2

1

Mass of calcium sulfate = 2.672 × 10–2 × 136.2 = 3.6398 = 3.64 (g) Answer must be to 3 significant figures

1 [11]

Q32. B

[1]

Q33. B

[1]

Q34. A

[1]

Q35. (a) Stage 1

Mr for Mg(NO3)2 = 148.3

Moles of Mg(NO3)2 = = 2.522 × 10-4 mol Extended response calculation

1

Stage 2

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Total moles of gas produced = 5/2 × moles of Mg(NO3)2

= 5/2 × 2.522 × 10–4 = 6.305 × 10–4

If ratio in stage 2 is incorrect, maximum marks for stage 3 is 2 1

Stage 3

PV = nRT so volume of gas V = nRT / P 1

V = = 1.745 × 10–5 m3

1

V = 1.745 × 10–5 × 1 × 106 = 17.45 cm3 = 17.5 (cm3) Answer must be to 3 significant figures (answer could be 17.4 cm3 dependent on intermediate values)

1

(b) Some of the solid is lost in weighing product / solid is blown away with the gas 1

[6]

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Atomic structure exam pack 1 new spec

Name: ________________________

Class: ________________________

Date: ________________________

Time: 229 minutes

Marks: 213 marks

Comments:

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Q1. This question is about the first ionisation energies of some elements in the Periodic Table.

(a) Write an equation, including state symbols, to show the reaction that occurs when the first ionisation energy of lithium is measured.

___________________________________________________________________ (1)

(b) State and explain the general trend in first ionisation energies for the Period 3 elements aluminium to argon.

Trend _____________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(c) There is a similar general trend in first ionisation energies for the Period 4 elements gallium to krypton.

State how selenium deviates from this general trend and explain your answer.

How selenium deviates from this trend ____________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________ (3)

(d) Suggest why the first ionisation energy of krypton is lower than the first ionisation energy of argon.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(e) The table below gives the successive ionisation energies of an element.

First Second Third Fourth Fifth

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Ionisation energy / kJ mol–1 590 1150 4940 6480 8120

Deduce the group in the Periodic Table that contains this element.

___________________________________________________________________ (1)

(f) Identify the element that has a 5+ ion with an electron configuration of 1s2 2s2 2p6 3s2 3p6 3d10

___________________________________________________________________ (1)

(Total 10 marks)

Q2. The manufacturer supplying concentrated ethanoic acid for the production of vinegar also supplied other acids. The label had come off a batch of one of these other acids. A sample of this unknown acid was analysed and found to contain 54.5% of carbon and 9.10% of hydrogen by mass, the remainder being oxygen.

(a) Use these data to calculate the empirical formula of the unknown acid. Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) A sample of the unknown acid was analysed in a mass spectrometer. The mass spectrum obtained is shown below.

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Use the mass spectrum to determine the Mr of the unknown acid.

___________________________________________________________________ (1)

(c) Use your answers from parts (a) and (b) to determine the molecular formula of the unknown acid. (If you could not answer part (b), you should assume that the Mr of the acid is 132.0 but this is not the correct value.) Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 6 marks)

Q3. The element rubidium exists as the isotopes 85Rb and 87Rb

(a) State the number of protons and the number of neutrons in an atom of the isotope 85Rb

Number of protons ___________________________________________________

Number of neutrons __________________________________________________ (2)

(b) (i) Explain how the gaseous atoms of rubidium are ionised in a mass spectrometer

______________________________________________________________

______________________________________________________________

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______________________________________________________________

______________________________________________________________ (2)

(ii) Write an equation, including state symbols, to show the process that occurs when the first ionisation energy of rubidium is measured.

______________________________________________________________ (1)

(c) The table shows the first ionisation energies of rubidium and some other elements in the same group.

Element sodium potassium rubidium

First ionisation energy / kJ mol–1 494 418 402

State one reason why the first ionisation energy of rubidium is lower than the first ionisation energy of sodium.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(d) (i) State the block of elements in the Periodic Table that contains rubidium.

______________________________________________________________ (1)

(ii) Deduce the full electron configuration of a rubidium atom.

______________________________________________________________ (1)

(e) A sample of rubidium contains the isotopes 85Rb and 87Rb only. The isotope 85Rb has an abundance 2.5 times greater than that of 87Rb

Calculate the relative atomic mass of rubidium in this sample. Give your answer to one decimal place.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

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(f) By reference to the relevant part of the mass spectrometer, explain how the abundance of an isotope in a sample of rubidium is determined.

Name of relevant part _________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(g) Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer.

Atomic radius of 88Sr compared to 87Rb ___________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 16 marks)

Q4. Define the term mass number of an atom.

The mass number of an isotope of nitrogen is 15. Deduce the number of each of the fundamental particles in an atom of 15N

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (Total 3 marks)

Q5. (a) Define the term relative atomic mass.

An organic fertiliser was analysed using a mass spectrometer. The spectrum showed that the nitrogen in the fertiliser was made up of 95.12% 14N and 4.88% 15N

Calculate the relative atomic mass of the nitrogen found in this organic fertiliser. Give your answer to two decimal places.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(b) In a mass spectrometer, under the same conditions, 14N+ and 15N+ ions follow different paths. State the property of these ions that causes them to follow different paths.

State one change in the operation of the mass spectrometer that will change the path of an ion.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) Organic fertilisers contain a higher proportion of 15N atoms than are found in synthetic fertilisers.

State and explain whether or not you would expect the chemical reactions of the nitrogen compounds in the synthetic fertiliser to be different from those in the organic fertiliser. Assume that the nitrogen compounds in each fertiliser are the same.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 8 marks)

Q6. Mass spectrometry can be used to identify isotopes of elements.

(a) (i) In terms of fundamental particles, state the difference between isotopes of an element.

______________________________________________________________

______________________________________________________________ (1)

(ii) State why isotopes of an element have the same chemical properties.

of 54

______________________________________________________________

______________________________________________________________ (1)

(b) Give the meaning of the term relative atomic mass.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (2)

(c) The mass spectrum of element X has four peaks. The table below gives the relative abundance of each isotope in a sample of element X.

m/z 64 66 67 68

Relative abundance 12 8 1 6

(i) Calculate the relative atomic mass of element X. Give your answer to one decimal place.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Use the Periodic Table to identify the species responsible for the peak at m/z = 64

______________________________________________________________ (2)

(d) Suggest one reason why particles with the same mass and velocity can be deflected by different amounts in the same magnetic field.

___________________________________________________________________

___________________________________________________________________ (1)

(e) Explain how the detector in a mass spectrometer enables the abundance of an isotope to be measured.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q7. The mass spectrum of a sample of krypton taken from a meteorite is shown below.

(a) Use this spectrum to calculate the relative atomic mass of this sample of krypton. Give your answer to one decimal place.

Explain why the value you have calculated is slightly different from the relative atomic mass given in the Periodic Table.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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(4)

(b) State how krypton is ionised in the mass spectrometer.

Write an equation, including state symbols, to show the reaction that occurs when the first ionisation energy of Kr is measured.

Sometimes the mass spectrum of Kr has a very small peak with an m/z value of 42. Explain the occurrence of this peak.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (5)

(Total 9 marks)

Q8. This question is about electron configuration.

(a) Give the full electron configuration of an Al atom and of a Cr3+ ion.

Al atom ____________________________________________________________

Cr3+ ion ____________________________________________________________ (2)

(b) Deduce the formula of the ion that has a charge of 2+ with the same electron configuration as krypton.

___________________________________________________________________ (1)

(c) Deduce the formula of the compound that contains 2+ ions and 3− ions that both have the same electron configuration as argon.

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___________________________________________________________________ (1)

(Total 4 marks)

Q9. (a) Use your knowledge of electron configuration and ionisation energies to answer this

question. The following diagram shows the second ionisation energies of some Period 3 elements.

(i) Draw an ‘X’ on the diagram to show the second ionisation energy of sulfur. (1)

(ii) Write the full electron configuration of the Al2+ ion.

______________________________________________________________ (1)

(iii) Write an equation to show the process that occurs when the second ionisation energy of aluminium is measured.

______________________________________________________________ (1)

(iv) Give one reason why the second ionisation energy of silicon is lower than the second ionisation energy of aluminium.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(b) Predict the element in Period 3 that has the highest second ionisation energy. Give a reason for your answer.

Element ____________________________________________________________

Reason ____________________________________________________________

___________________________________________________________________

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___________________________________________________________________ (2)

(c) The following table gives the successive ionisation energies of an element in Period 3.

First Second Third Fourth Fifth Sixth

Ionisation energy / kJ mol−1 786 1580 3230 4360 16100 19800

Identify this element.

___________________________________________________________________ (1)

(d) Explain why the ionisation energy of every element is endothermic.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (1)

(Total 8 marks)

Q10. (a) Nickel is a metal with a high melting point.

(i) State the block in the Periodic Table that contains nickel.

______________________________________________________________ (1)

(ii) Explain, in terms of its structure and bonding, why nickel has a high melting point.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(iii) Draw a labelled diagram to show the arrangement of particles in a crystal of nickel. In your answer, include at least six particles of each type.

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(2)

(iv) Explain why nickel is ductile (can be stretched into wires).

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(b) Nickel forms the compound nickel(II) chloride (NiCl2).

(i) Give the full electron configuration of the Ni2+ ion.

______________________________________________________________ (1)

(ii) Balance the following equation to show how anhydrous nickel(II) chloride can be obtained from the hydrated salt using SOCl2

Identify one substance that could react with both gaseous products.

......NiCl2.6H2O(s) + ...... SOCl2(g) ......NiCl2(s) + ......SO2(g) + ......HCl(g)

Substance ____________________________________________________ (2)

(Total 9 marks)

Q11. (a) State the meaning of the term mass number of an isotope.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(b) Give the symbol of the element that has an isotope with a mass number of 68 and has 38 neutrons in its nucleus.

___________________________________________________________________ (1)

(c) The following shows a simplified diagram of a mass spectrometer.

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(i) State what happens to the sample in the parts labelled P and Q.

P ____________________________________________________________

Q ____________________________________________________________ (2)

(ii) In a mass spectrometer, the isotopes of an element are separated. Two measurements for each isotope are recorded on the mass spectrum.

State the two measurements that are recorded for each isotope.

Measurement 1 _________________________________________________

Measurement 2 _________________________________________________ (2)

(d) A sample of element R contains isotopes with mass numbers of 206, 207 and 208 in a 1:1:2 ratio of abundance.

(i) Calculate the relative atomic mass of R. Give your answer to one decimal place.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Identify R.

______________________________________________________________ (1)

(iii) All the isotopes of R react in the same way with concentrated nitric acid.

State why isotopes of an element have the same chemical properties.

______________________________________________________________

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______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (1)

(Total 11 marks)

Q12. The mass spectrum of the isotopes of element X is shown in the diagram.

m / z

(a) Define the term relative atomic mass.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) Use data from the diagram to calculate the relative atomic mass of X.


___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

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(c) Identify the ion responsible for the peak at 72

___________________________________________________________________ (1)

(d) Identify which one of the isotopes of X is deflected the most in the magnetic field of a mass spectrometer. Give a reason for your answer.

Isotope ____________________________________________________________

Reason ____________________________________________________________ (2)

(e) In a mass spectrometer, the relative abundance of each isotope is proportional to the current generated by that isotope at the detector.

Explain how this current is generated.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(f) X and Zn are different elements.

Explain why the chemical properties of 70X and 70Zn are different.

___________________________________________________________________

___________________________________________________________________ (1)

(Total 11 marks)

Q13. (a) Table 1 shows some data about fundamental particles in an atom.

Table 1

Particle proton neutron electron

Mass / g 1.6725 × 10–24 1.6748 × 10–24 0.0009 × 10–24

(i) An atom of hydrogen can be represented as 1H

Use data from Table 1 to calculate the mass of this hydrogen atom.

______________________________________________________________ (1)

(ii) Which one of the following is a fundamental particle that would not be deflected by an electric field?

A electron

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B neutron

C proton

Write the correct letter, A, B or C, in the box.

(1)

(b) A naturally occurring sample of the element boron has a relative atomic mass of 10.8. In this sample, boron exists as two isotopes, 10B and 11B

(i) Calculate the percentage abundance of 10B in this naturally occurring sample of boron.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) State, in terms of fundamental particles, why the isotopes 10B and 11B have similar chemical reactions.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(c) Complete Table 2 by suggesting a value for the third ionisation energy of boron.

Table 2

First Second Third Fourth Fifth

Ionisation energy / kJ mol–

1 799 2420 25 000 32 800

(1)

(d) Write an equation to show the process that occurs when the second ionisation energy of boron is measured. Include state symbols in your equation.

___________________________________________________________________ (1)

(e) Explain why the second ionisation energy of boron is higher than the first ionisation energy of boron.

___________________________________________________________________

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___________________________________________________________________ (1)

(Total 8 marks)

Q14. The successive ionisation energies for element X are shown in the following graph.

Which element is X?

A Nitrogen

B Phosphorus

C Aluminium

D Boron (Total 1 mark)

Q15. Tellurium is the element with atomic number of 52

(a) Using information from the Periodic Table, complete the electron configuration of tellurium.

[Kr] ______________________________________________________________ (1)

(b) The mass spectrum of a sample of tellurium is shown in the graph.

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(i) Use the graph to calculate the relative atomic mass of this sample of tellurium. Give your answer to one decimal place.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Suggest what might cause the relative atomic mass of this sample to be different from the relative atomic mass given in the Periodic Table.

______________________________________________________________

______________________________________________________________ (1)

(c) Write an equation for the reaction that occurs when a tellurium ion hits the detector.

___________________________________________________________________ (1)

(d) State the m / z value of the ions that produce the biggest current at the detector when the spectrum in the graph is recorded. Give a reason for your answer.

m / z value _________________________________________________________

Reason ____________________________________________________________

___________________________________________________________________

___________________________________________________________________

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(2)

(e) The mass spectrum of tellurium also has a small peak at m / z = 64

Explain the existence of this peak.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(f) Predict whether the atomic radius of 124Te is larger than, smaller than or the same as the atomic radius of 130Te Explain your answer.

Atomic radius of 124Te compared to 130Te __________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q16. (a) Explain how ions are accelerated, detected and have their abundance determined in

a time of flight (TOF) mass spectrometer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Calculate the mass, in kg, of a single 52Cr+ ion. Assume that the mass of a 52Cr+ ion is the same as that of a 52Cr atom.

(The Avogadro constant L = 6.022 × 1023 mol−1)

___________________________________________________________________

___________________________________________________________________ (1)

(c) In a TOF mass spectrometer the kinetic energy (KE) of a 52Cr+ ion was

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1.269 × 10−13 J

Calculate the velocity of the ion using the equation.

(m = mass/kg and v = velocity/ms−1)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) Bromine has two isotopes, 79Br and 81Br, in approximately equal abundance. In a TOF mass spectrometer bromine forms ions with formula [Br2]+

Sketch the pattern of peaks you would expect to see in the mass spectrum of a sample of bromine.

(2)

(e) A sample of xenon has Ar = 131.31. The sample consists of four isotopes. The abundances of three of the isotopes are shown in the table below. The data for one of the isotopes, mXe, is missing.

Isotope 129Xe 131Xe 132Xe mXe

% abundance 28.0 25.0 27.0 To be

calculated

Use the data to calculate the abundance of isotope mXe and calculate m, the mass number of mXe. Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 12 marks)

Q17. Ions of two isotopes of iron are

53Fe2+ 56Fe2+

Which statement is correct?

A The ions of both the isotopes have the electronic configuration 1s22s22p63s23p64s23d6

B The ions of both the isotopes contains 26 neutrons

C 53Fe2+ has fewer protons than 56Fe2+

D After acceleration to the same kinetic energy 56Fe2+ will move more slowly than 53Fe2+

(Total 1 mark)

Q18. This question is about Period 3 of the Periodic Table.

(a) Deduce which of Na+ and Mg2+ is the smaller ion. Explain your answer.

Smaller ion _________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) Write an equation to represent the process that occurs when the first ionisation energy for sodium is measured.

___________________________________________________________________ (1)

(c) The first ionisation energies of some Period 3 elements are shown in the following graph.

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Complete the graph by plotting the approximate first ionisation energy values for magnesium and sulfur.

Explain why the first ionisation energy of sulfur is different from that of phosphorus.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 7 marks)

Q19. Which of these atoms has the largest atomic radius?

A Ar

B Cl

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C Mg

D Na

(Total 1 mark)

Q20. This question is about the elements in Group 2 and their compounds.

(a) Use the Periodic Table to deduce the full electron configuration of calcium.

___________________________________________________________________ (1)

(b) Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water.

___________________________________________________________________ (1)

(c) State the role of water in the reaction with calcium.

___________________________________________________________________ (1)

(d) Write an equation to show the process that occurs when the first ionisation energy of calcium is measured.

___________________________________________________________________ (1)

(e) State and explain the trend in the first ionisation energies of the elements in Group 2 from magnesium to barium.

Trend ______________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 7 marks)

Q21. Which change requires the largest amount of energy?

A He+(g) He2+(g) + e–

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B Li(g) Li+(g) + e–

C Mg+(g) Mg2+(g) + e–

D N(g) N+(g) + e– (Total 1 mark)

Q22. A sample of ethanedioic acid was treated with an excess of an unknown alcohol in the presence of a strong acid catalyst. The products of the reaction were separated and analysed in a time of flight (TOF) mass spectrometer. Two peaks were observed at m / z = 104 and 118.

(a) Identify the species responsible for the two peaks.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) Outline how the TOF mass spectrometer is able to separate these two species to give two peaks.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 6 marks)

Q23. Which of these atoms has the smallest number of neutrons?

A 3H

B 4He

C 5He

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D 4Li (Total 1 mark)

Q24. Bromine exists as two isotopes 79Br and 81Br, which are found in almost equal abundance.

Which of the statements is correct?

A The first ionisation energy of 79Br is less than the first ionisation energy of 81Br

B The atomic radius of 79Br is less than the atomic radius of 81Br

C The mass spectrum of C3H7Br has two molecular ion peaks at 122 and 124

D 79Br is more reactive than 81Br (Total 1 mark)

Q25. (a) A sample of sulfur consisting of three isotopes has a relative atomic mass of 32.16.

The following table gives the relative abundance of two of these isotopes.

Mass number of isotope 32 33

Relative abundance / % 91.0 1.8

Use this information to determine the relative abundance and hence the mass number of the third isotope. Give your answer to the appropriate number of significant figures.

Mass number = ____________________ (4)

(b) Describe how ions are formed in a time of flight (TOF) mass spectrometer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________ (2)

(c) A TOF mass spectrometer can be used to determine the relative molecular mass of molecular substances.

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 8 marks)

Q26. This question is about time of flight (TOF) mass spectrometry.

(a) The mass spectrum of element Q has peaks with m/z values shown in the table.

m/z 82 83 84 86

Relative intensity 5 3 26 7

Calculate the relative atomic mass of Q and give your answer to one decimal place. Identify the element Q.

Relative atomic mass of Q ________

Element Q ____________________ (3)

(b) A sample of the element Q consists of several isotopes. All of the Q+ ions in the sample of Q that has been ionised in a TOF mass spectrometer have the same kinetic energy.

kinetic energy of each ion = mv2

where m is the mass, in kg, of one ion of an isotope and v is the velocity of an ion in m s−1

where d is the length, in m, of the flight tube and t is the time taken, in s, for an ion to reach the detector

The time of flight of a 82Q+ ion is 1.243 × 10−5 s.

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Calculate the time of flight of the 86Q+ ion.

Time of flight of the 86Q+ ion _____ s (3)

(Total 6 marks)

Q27. What are the numbers of neutrons and electrons in the 57Fe2+ ion?

Neutrons Electrons

A 31 24

B 57 24

C 31 26

D 57 28 (Total 1 mark)

Q28. Which of these correctly shows the numbers of sub-atomic particles in a 41K+ ion?

Number of electrons

Number of protons

Number of neutrons

A 19 19 20

B 18 20 21

C 18 19 22

D 19 18 23 (Total 1 mark)

Q29. Element Q forms a sulfate with formula QSO4

Which of these could represent the electronic configuration of an atom of Q?

A [Ne]3s1

B [Ne]3s2

C [Ne]3s23p1

D [Ne]3s13p2

(Total 1 mark)

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Q30. Chlorine exists as two isotopes 35Cl and 37Cl in the ratio 3:1

Which statement about peaks in the mass spectrum of Cl2 is correct?

A Peaks at m/z = 70 and 74 in the ratio 3:1

B Peaks at m/z = 70, 72 and 74 in the ratio 9:6:1

C Peaks at m/z = 70, 72 and 74 in the ratio 9:3:1

D Peaks at m/z = 70 and 72 in the ratio 3:1 (Total 1 mark)

Q31. Magnesium exists as three isotopes: 24Mg, 25Mg and 26Mg

(a) In terms of sub-atomic particles, state the difference between the three isotopes of magnesium.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(b) State how, if at all, the chemical properties of these isotopes differ.

Give a reason for your answer.

Chemical properties __________________________________________________

___________________________________________________________________

Reason ____________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) 25Mg atoms make up 10.0% by mass in a sample of magnesium.

Magnesium has Ar = 24.3

Use this information to deduce the percentages of the other two magnesium isotopes present in the sample.

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24Mg percentage = ________ % 26Mg percentage = ________ % (4)

(d) In a TOF mass spectrometer, ions are accelerated to the same kinetic energy (KE).

where m = mass (kg) and v = velocity (m s−1)

where d = distance (m) and t = time (s)

In a TOF mass spectrometer, each 25Mg+ ion is accelerated to a kinetic energy of 4.52 × 10−16 J and the time of flight is 1.44 × 10−5 s. Calculate the distance travelled, in metres, in the TOF drift region. (The Avogadro constant L = 6.022 × 1023 mol−1)

Distance = __________________ m (4)

(Total 11 marks)

Q32. A sample of titanium was ionised by electron impact in a time of flight (TOF) mass spectrometer. Information from the mass spectrum about the isotopes of titanium in the sample is shown in the table.

m/z 46 47 48 49

Abundance / % 9.1 7.8 74.6 8.5

(a) Calculate the relative atomic mass of titanium in this sample.


Relative atomic mass of titanium in this sample ____________________ (2)

(b) Write an equation, including state symbols, to show how an atom of titanium is ionised by electron impact and give the m/z value of the ion that would reach the detector first.

Equation ___________________________________________________________

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m/z value ___________________________________________________________ (2)

(c) Calculate the mass, in kg, of one atom of 49Ti

The Avogadro constant L = 6.022 × 1023 mol−1

Mass ____________________ kg (1)

(d) In a TOF mass spectrometer the time of flight, t, of an ion is shown by the equation

In this equation d is the length of the flight tube, m is the mass, in kg, of an ion and E is the kinetic energy of the ions.

In this spectrometer, the kinetic energy of an ion in the flight tube is 1.013 × 10−13 J

The time of flight of a 49Ti+ ion is 9.816 × 10−7 s

Calculate the time of flight of the 47Ti+ ion.


Time of flight ____________________ s (3)

(Total 8 marks)

Q33. Which of these has the highest first ionisation energy?

A Na

B Al

C Si

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D Cl (Total 1 mark)

Q34. Which statement about time of flight mass spectrometry is correct?

A The current in the detector is proportional to the ion abundance

B Sample particles gain electrons to form positive ions

C Particles are detected in the order of their kinetic energies

D Ions are accelerated by a magnetic field (Total 1 mark)

Q35. This question is about atomic structure.

(a) Write the full electron configuration for each of the following species.

Cl−________________________________________________________________

Fe2+_______________________________________________________________ (2)

(b) Write an equation, including state symbols, to represent the process that occurs when the third ionisation energy of manganese is measured.

___________________________________________________________________

___________________________________________________________________ (1)

(c) State which of the elements magnesium and aluminium has the lower first ionisation energy.


___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

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(d) A sample of nickel was analysed in a time of flight (TOF) mass spectrometer. The sample was ionised by electron impact ionisation. The spectrum produced showed three peaks with abundances as set out in the table.

m/z Abundance / %

58 61.0

60 29.1

61 9.9

Give the symbol, including mass number, of the ion that would reach the detector first in the sample.

Calculate the relative atomic mass of the nickel in the sample.


Symbol of ion _______________________________________________________

Relative atomic mass _________________________________________________ (3)

(Total 9 marks)

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Mark schemes

Q1. (a) Li(g) → Li+(g) + e-(g)

Li(g) - e-(g) → Li+(g)

Li(g) + e-(g) → Li+(g) + 2e-

One mark for balanced equation with state symbols Charge and state on electron need not be shown

1

(b) Increases If trend wrong then CE = 0/3 for (b). If blank mark on.

1

Increasing nuclear charge / increasing no of protons Ignore effective with regard to nuclear charge

1

Same or similar shielding / same no of shells / electron (taken) from same (sub)shell / electron closer to the nucleus / smaller atomic radius

1

(c) Lower If not lower then CE = 0/3

1

Paired electrons in a (4) p orbital If incorrect p orbital then M2 = 0

1

(Paired electrons) repel If shared pair of electrons M2 + M3 = 0

1

(d) Kr is a bigger atom / has more shells / more shielding in Kr / electron removed further from nucleus/ electron removed from a higher (principal or main) energy level

CE if molecule mentioned Must be comparative answer QWC

1

(e) 2 / two / II 1

(f) Arsenic / As 1

[10]

Q2. (a) Percentage of oxygen is 36.4%

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% of oxygen stated or shown in calculation. 1

Correct calculation of ratios (C 4.54, H 9.10, O 2.28) Mark is for correct method, dividing % by Ar

1

Empirical formula C2H4O Allow consequential answer from wrong percentage of oxygen (max 2 marks).

1

(b) 88 Accept 88.0 Do not penalise correct answer in g.

1

(c) Ratio MF / EF of 2 (88 / 44.0 = 2) If use 132 / 44 = 3, molecular formula C6H12O3 scores 2 marks.

1

Molecular formula is C4H8O2

Accept consequential answers from (a) and (b) 1

[6]

Q3. (a) 37

These answers only. Allow answers in words.

1

48 Ignore any sum(s) shown to work out the answers.

1

(b) (i) Electron gun / high speed/high energy electrons Not just electrons. Not highly charged electrons.

1

Knock out electron(s) Remove an electron.

1

(ii) Rb(g) → Rb+(g) + e(–)

OR Rb(g) + e(–) → Rb+(g) + 2e(–)

OR Rb(g) - e(–) → Rb+(g)

Ignore state symbols for electron. 1

(c) Rb is a bigger (atom) / e further from nucleus / electron lost from a higher energy level/ More shielding in Rb / less attraction of nucleus in Rb for outer electron / more shells

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Answer should refer to Rb not Rb molecule If converse stated it must be obvious it refers to Na Answer should be comparative.

1

(d) (i) s / block s / group s Only

1

(ii) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1

Allow 3d10 before 4s2

Allow in any order. 1

(e) (85 × 2.5) + 87 ×1 3.5

M1 is for top line 1 1

= 85.6 Only

1

OR

(58 × 5) + 87 ×2 7

M185Rb 71.4% and 87Rb 28.6% M2 divide by 100

1 1

85.6 M3 = 85.6

1

(f) Detector Mark independently Allow detection (plate).

1

Current / digital pulses / electrical signal related to abundance Not electrical charge.

1

(g) Smaller Chemical error if not smaller, CE = 0/3 If blank mark on.

1

Bigger nuclear charge / more protons in Sr Not bigger nucleus.

1

Similar/same shielding QWC

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(Outer) electron entering same shell/sub shell/orbital/same number of shells. Do not allow incorrect orbital.

1 [16]

Q4. Mass number = number of protons + neutrons (in the nucleus/atom)

Not in a substance or compound or element 1

7 protons and 7 electrons 1

8 neutrons 1

[3]

Q5. (a) Average/mean mass of (1) atom(s) (of an element)

1

1/12 mass of one atom of 12C Accept answer in words Can have top line × 12 instead of bottom line ÷ 12

1

OR

(Average) mass of one mole of atoms 1/12 mass of one mole of 12C

OR

(Weighted) average mass of all the isotopes 1/12 mass of one atom of 12C

OR

Average mass of an atom/isotope compared to C-12 on a scale in which an atom of C-12 has a mass of 12

Allow 95.12 + 4.88 instead of 100

1

= 14.05 If not to 2 d.p. then lose last mark Not 14.04

1

(b) 15N is heavier/15N has a bigger m/z/different m/z values Not different no’s of neutrons Not ionisation potential

1

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Electromagnet/electric field/magnet/accelerating potential or voltage/electric current

1

(c) No difference 1

Same no of electrons (in outer orbital/shell/sub shell)/same electron configuration

M2 dependent on M1 Not just electrons determine chemical properties Ignore protons

1 [8]

Q6. (a) (i) Different number / amount of neutrons

Not different neutrons Ignore same protons and/or electrons CE incorrect statement relating to protons / electrons

1

(ii) Same electron configuration / same number of electrons (in the outer shell)

Ignore same no of protons Ignore electrons determine chemical properties CE if wrong statement relating to protons / neutrons

1

(b) Average mass of 1 atom (of an element) 1/12 mass atom of 12C

OR

Average/mean mass of atoms of an element 1/12 mass of one atom of 12C

OR


OR


OR

Average mass of an atom/isotope compared to C-12 on a scale in which an atom of C-12 has a mass of 12

If moles and atoms mixes Max = 1 Mark top and bottom line independently 1/12 on bottom line can be represented as x 12 on top line This expression = 2 marks

2

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(c) (i)

= 65.6 If not 27 max 1 mark (for top line) Mark is for dividing by 27 or string If evidence of arithmetic or transcription error seen in M1 or M2 allow consequential M3 and consequential (c)(ii) 65.6 = 3 marks

3

(ii) 64Zn+

M1 for identifying Zn / zinc M2 is for the + sign and the 64 M2 is dependent on M1

2

(d) Size of the charge (on the ion) / different charges / different m/z Allow forms 2+ ions QWC

1

(e) (ions hit detector and) cause current/(ions) accept electrons/cause electron flow/electric pulse caused bigger current = more of that isotope/current proportional to abundance

Implication that current depends on the number of ions M2 dependent on M1

2 [12]

Q7.

(a)

M1 for the top line M2 is for division by 17

1

= 84.0 Not 84 No consequential marking from M1 or M2 Ignore units

1

The Ar in the Periodic table takes account of the other isotopes / different amounts of isotopes (or words to that effect regarding isotopes)

Award independently Comparison implied Isotope(s) alone, M4 = 0

1

(b) (Beam of electrons from) an electron gun / high speed / high energy electrons

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1

Knocks out electron(s) (to form a positive ion) 1

Kr(g) + e– → Kr+(g) + 2e(–) State symbols must clearly be (g)

1

OR

Kr(g) → Kr+(g) + e(–) / Kr(g) – e(–) → Kr+(g)

The 84Kr isotope One mark for identifying the 84 isotope

1

Has 2 electrons knocked out / gets a 2+ charge One mark for the idea of losing 2 electrons (from this isotope)

1 [9]

Q8. (a) 1s22s22p63s23p1

1

1s22s22p63s23p63d3

1

If noble gas core used correctly in both then scores 1 Allow subscripts and capitals Ignore 4s0

(b) Sr2+

Ignore name and correct proton/mass number Allow Sr+2

1

(c) Ca3P2

Allow reversed or ionic formula Ignore name

1 [4]

Q9. (a) (i) Higher than P

1

(ii) 1s2 2s2 2p6 3s1

Allow any order 1

(iii) Al+(g) + e (−) Al2+(g) + 2e(−)

OR Al+(g) Al2+(g) + e(−)

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OR Al+(g) − e(−) Al2+(g)

1

(iv) Electron in Si (removed from) (3)p orbital / electron (removed) from higher energy orbital or sub-shell / electron in silicon is more shielded

Accept converse arguments relating to Al Penalise incorrect p-orbital

1

(b) Sodium / Na Allow Na+

1

Electron (removed) from the 2nd shell / 2p (orbital) M2 is dependent on M1 Allow electron from shell nearer the nucleus (so more attraction)

1

(c) Silicon / Si Not SI

1

(d) Heat or energy needed to overcome the attraction between the (negative) electron and the (positive) nucleus or protons

Not breaking bonds QoL

Or words to that effect eg electron promoted to higher energy level (infinity) so energy must be supplied

1 [8]

Q10. (a) (i) d (block) OR D (block)

Ignore transition metals / series. Do not allow any numbers in the answer.

1

(ii) Contains positive (metal) ions or protons or nuclei and delocalised / mobile / free / sea of electrons

Ignore atoms. 1

Strong attraction between them or strong metallic bonds Allow ‘needs a lot of energy to break / overcome’ instead of ‘strong’. If strong attraction between incorrect particles, then CE = 0 / 2. If molecules / intermolecular forces / covalent bonding / ionic bonding mentioned then CE=0.

1

(iii)

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M1 is for regular arrangement of atoms / ions (min 6 metal particles). M2 for + sign in each metal atom / ion. Allow 2+ sign.

2

(iv) Layers / planes / sheets of atoms or ions can slide over one another QoL.

1

(b) (i) 1s2 2s2 2p6 3s2 3p6 3d8 (4s0) Only.

1

(ii) NiCl2.6H2O + 6 SOCl2 NiCl2 + 6 SO2 + 12 HCl Allow multiples.

1

NaOH / NH3 / CaCO3 / CaO Allow any name or formula of alkali or base. Allow water.

1 [9]

Q11. (a) (Total number of) protons and neutrons (in nucleus of atom)

(number of) nucleons 1

(b) Zn Do not allow Zn−1 or Zn+1 or ZN Ignore numbers

1

(c) (i) P = ionise (sample) Allow removing an electron / forms (+) ions

1

Q = accelerate (sample) Allow speeds (ions) up Penalise molecules / atoms

1

(ii) m / z Allow mass / charge

1

(relative) abundance / (relative) intensity QoL Allow M1 + M2 in any order

1

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(d) (i) M1 = topline

1

M2 = ÷ 4 1

= 207.3 Only 207.3 = 3 marks

1

(ii) Lead / Pb Not PB

1

(iii) Same number of electrons (in outer shell) / same electronic configuration Ignore electrons determine chemical properties Ignore reference to p and n if correct Penalise if incorrect

1 [11]

Q12. (a) Average / mean mass of 1 atom (of an element)

1/12 mass of one atom of 12C If moles and atoms mixed, max = 1

1

Mark top and bottom line independently. All key terms must be present for each mark.

1

OR

Average / mean mass of atoms of an element 1/12 mass of one atom of 12C

OR

Average / mean mass of atoms of an element ×12 mass of one atom of 12C

OR


OR


OR

Average mass of an atom / isotope (compared to C−12) on a scale in which an atom of C−12 has a mass of 12

This expression = 2 marks.

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(b) 1 1

= 72.4 72.4 only

1

(c) (72)Ge+ or germanium+

Must show ‘+’ sign. Penalise wrong mass number

1

(d) 70 If M1 incorrect or blank CE = 0/2 Ignore symbols and charge even if wrong.

1

Lowest mass / lowest m/z Accept lightest. Accept fewest neutrons.

1

(e) Electron(s) transferred / flow (at the detector) M1 must refer to electron flow at the detector. If M1 incorrect CE = 0/2

1

(From detector / plate) to the (+) ion Do not allow from a charged plate.

1

(f) They do not have the same electron configuration / they have different number of electrons (in the outer shell)

Ignore electrons determine the properties of an atom. Ignore they are different elements or different number of protons.

1 [11]

Q13. (a) (i) 1.6734 × 10−24 (g)

Only.

1.6734 × 10−27 kg Not 1.67 × 10−24 (g).

1

(ii) B 1

(b) (i) = 10.8

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OR ratio 10:11 = 1:4 OR 20:80 etc Allow idea that there are 5 × 0.2 divisions between 10 and 11.

1

abundance of 10B is 20(%)

OR

= 10.8

10x + 1100 − 11x = 1080

∴ x = 1100 − 1080 = 20% Correct answer scores M1 and M2.

1

(ii) Same number of electrons (in outer shell or orbital) Ignore electrons determine chemical properties.

Same electronic configuration / arrangement Ignore protons unless wrong.

1

(c) Range between 3500 and 10 000 kJ mol−1

1

(d) B+(g) B2+(g) + e(−)

B+(g) − e(−) B2+(g)

B+(g) + e(−) B2+(g) + 2e(−)

Ignore state symbol on electron even if wrong. 1

(e) Electron being removed from a positive ion (therefore needs more energy) / electron being removed is closer to the nucleus

Must imply removal of an electron. Allow electron removed from a + particle / species or from a 2+ ion. Not electron removed from a higher / lower energy level / shell. Not electron removed from a higher energy sub-level / orbital. Ignore electron removed from a lower energy sub-level / orbital. Ignore ‘more protons than electrons’. Not ‘greater nuclear charge’. Ignore ‘greater effective nuclear charge’. Ignore shielding.

1 [8]

Q14. C

[1]

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Q15. (a) 5s2 4d10 5p4 / 4d10 5s2 5p4

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4

or 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p4

Allow any order but must finish with 5p4

1

(b) (i) or M1 for top line

1

127.8 M2 for correct denominator

1

127.8 with no working shown scores 3 marks 1

Or

1

Mark for 100 dependent on top line correct 1

127.8 1

(ii) Other isotopes present / some isotopes absent / different abundances of isotopes

1

(c) Te+ + e(−) Te Ignore state symbols Allow Te2+ + 2e(−) Te

1

(d) 128 Only

1

Most abundant ion (QoL − superlative) M2 dependent on correct M1

1

(e) 2+ ion formed / 2 electrons removed Due to 128Te2+ = 2 marks

1

From 128 (Te) Mark independently

1

(f) Same

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If not same CE = 0 / 2 1

(Each isotope has the) same number of protons / same nuclear charge and same number of electrons / electronic configuration

Ignore more neutrons in 130Te 1

[12]

Q16. (a) (Ions accelerated by) attraction to negatively charged plate /

electric field Mark independently

1

Ions detected by gaining electrons Allow the transfer of electrons

1

Abundance determined by (size) of current flowing (or amount of electrons gained) in the detector

Allow current is proportional to abundance 1

(b) Mass =

Mass = 8.6(4) × 10−26

1

(c) V2 = (2 × 1.269 × 10−13) / 8.64 × 10−26

Allow correct rearrangement for V or V2

1

V = 1.71 × 106 ms−1

Allow ecf from (b) (note if 8.6 × 10−23 in (b) leads to approx. 5.4 × 104 ms−1)

1

(d) Sketch with peaks at 158, 160, 162 Mark independently

1

In ratio 25%:50%:25% Allow approx. ratio 1:2:1

1

(e) % abundance mXe = 20(%) Working must be shown

1

131.31 = (0.28*129) + (0.25*131) + (0.27*132) + (0.20*m) 1

131.31 – 104.51 = 0.2m 1

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Mass number = 134 Answer must be an integer

1 [12]

Q17. D

[1]

Q18. (a) Mg(2+) or Magnesium

Na+ CE=0 1

Because Mg2+ has more protons AND With the same shielding/screening/electron arrangement/number of electrons (or isoelectronic)

Allow larger/stronger nuclear charge Ignore atomic radius

1

(b) Na(g) → Na+(g) + e−

1 for correct species and gas phase Allow e without charge Allow Na(g) – e− → Na+(g) Na(g) + e− → Na+(g) + 2e−

1

(c) Mg between 600-800 1

S between 800-1040 If S not lower than P on graph then M1 only If no plots on graph must state S below P to access M3 & M4

1

e− paired in (3)p orbital in S (owtte) Allow (3)p subshell/sublevel provided pair mentioned

1

Paired e− repel (so less energy needed to remove) 1

[7]

Q19. D

[1]

Q20. (a) 1s22s22p63s23p64s2

Allow correct numbers that are not superscripted 1

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(b) Ca(s)+ 2H2O(l) Ca2+(aq) + 2OH–(aq) + H2(g) State symbols essential

1

(c) Oxidising agent 1

(d) Ca(g) Ca+(g) + e–

State symbols essential Allow ‘e’ without the negative sign

1

(e) Decrease If answer to ‘trend’ is not ‘decrease’, then chemical error = 0 / 3

1

Ions get bigger / more (energy) shells Allow atoms instead of ions

1

Weaker attraction of ion to lost electron 1

[7]

Q21. A

[1]

Q22. (a) [CH3OCOCOOH]+

Allow names 1

[CH3OCOCOOCH3]+

Do not allow molecular formula 1

(b) Positive ions are accelerated by an electric field 1

To a constant kinetic energy 1

The positive ions with m / z of 104 have the same kinetic energy as those with m / z of 118 and move faster

1

Therefore, ions with m / z of 104 arrive at the detector first 1

[6]

Q23. D

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[1]

Q24. C

[1]

Q25. (a) Abundance of third isotope = 100 – 91.0 –1.8 = 7.2%

1

= 32.16 1

7.2y = 32.16 × 100 – 32 × 91 – 33 × 1.8 = 244.6 1

y = 244.6 / 7.2 = 33.97

y = 34 Answer must be rounded to the nearest integer

1

(b) (for electrospray ionisation)

A high voltage is applied to a sample in a polar solvent 1

the sample molecule, M, gains a proton forming MH+

1

OR

(for electron impact ionisation)

the sample is bombarded by high energy electrons 1

the sample molecule loses an electron forming M+

1

(c) Ions, not molecules, will interact with and be accelerated by an electric field 1

Only ions will create a current when hitting the detector 1

[8]

Q26.

(a) 1

84.0 1

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Kr 1

(b) 82/(1.243 × 10−5)2 = 86 / t2

So t2 = 86 / 82 × (1.243 × 10−5)2

1

t2 = 1.6204 × 10−10

1

t = 1.273 × 10−5 (s) 1

[6]

Q27. A

[1]

Q28. C

[1]

Q29. B

[1]

Q30. B

[1]

Q31. (a) 24Mg has 12n; 25Mg has 13n; 26Mg has 14n

OR They have different numbers of neutrons 1

(b) No difference in chemical properties 1

Because all have the same electronic structure (configuration)

OR they have the same number of outer electrons 1

(c) If fraction with mass 24 = x

Fraction with mass 26 = 0.900 − x

Fraction with mass 25 = 0.100 1

Ar = 24x + (25 × 0.100) + 26(0.900 − x)

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1

24.3 = 24x + 2.50 + 23.4 −26x

2x = 1.60

x = 0.800 i.e. percentage 24Mg = 80.0(%) (80.0% 3sf) 1

26Mg = 0.900 − 0.800 = 0.100 ie percentage 26Mg = 10.0(%) 1

(d) m = 1

v2 = 2ke/m or v2 = 1

1

D = vt =1.48 × 105 × 1.44 × 10−5

D = 2.13 (m) 1

[11]

Q32.

(a) 1

= 47.8 Correct answer scores 2 marks. Allow alternative methods. Allow 1dp or more. Ignore units

1

(b) Ti(g) → Ti+(g) +e−

or Ti(g) + e−→ Ti+(g) +2e−

or Ti(g) − e−→ Ti+(g) State symbols essential Allow electrons without − charge shown.

1

46 1

(c) 8.1(37) × 10−26

1

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(d) M1 is for re-arranging the equation

Allow t α square root of m

1

Or

d = 1.5(47) This scores 2 marks Allow this expression for M2

1

= 9.6(14) × 10−7

Correct answer scores 3 marks. 1

[8]

Q33. D

[1]

Q34. A

[1]

Q35. (a) Cl− 1s22s22p63s23p6

1 Fe2+1s22s22p63s23p63d6

1

If [Ne] or [Ar] used then Max 1if both correct Ignore 4s0

Allow subscripts

(b) Mn2+ (g) ⟶ Mn3+ (g) + e−

1

States symbols are required Allow Mn2+ (g) − e− ⟶ Mn3+ (g) Negative charge needed on electron

(c) Al Mg then CE = 0

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1 (Outer) electron in (3)p sublevel / orbital

Not just level or shell 1

Higher in energy / further from the nucleus so easier to remove OWTTE

Both required for M3 1

Ignore shielding

(d) 58Ni+

M1 needs mass and charge – allow subscripts 1

Ar= [(58 × 61.0) + (60 × 29.1) + (61 × 9.9)] / 100 1

Ar= 58.9 must be to 1dp 1

[9]

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Bonding exam pack

Name: ________________________

Class: ________________________

Date: ________________________

Time: 209 minutes

Marks: 190 marks

Comments:

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Q1. This question is about the periodicity of the Period 3 elements.

(a) State and explain the general trend in first ionisation energy across Period 3.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(b) Give one example of an element which deviates from the general trend in first ionisation energy across Period 3.

Explain why this deviation occurs.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) The table shows successive ionisation energies of an element Y in Period 3.

Ionisation number 1 2 3 4 5 6 7 8

Ionisation energy / kJ mol–1 1000 2260 3390 4540 6990 8490 27 100 31 700

Identify element Y.

Explain your answer using data from the table.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) Identify the Period 3 element that has the highest melting point.

Explain your answer by reference to structure and bonding.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 13 marks)

Q2. The table shows some data about the elements bromine and magnesium.

Element Melting point / K Boiling point / K

Bromine 266 332

Magnesium 923 1383

In terms of structure and bonding explain why the boiling point of bromine is different from that of magnesium. Suggest why magnesium is a liquid over a much greater temperature range compared to bromine.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

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_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________ (Total 5 marks)

Q3. (a) Van der Waals’ forces exist between all molecules.

Explain how these forces arise.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) The table shows the boiling points of methanol (CH3OH) and methanethiol (CH3SH).

Compound Boiling point / °C

Methanol 65

Methanethiol 6

(i) Explain, in terms of their intermolecular forces, why the boiling points of these compounds are different.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

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(ii) Suggest how a mixture of methanol and methanethiol could be separated.

______________________________________________________________

______________________________________________________________ (1)

(c) Suggest why methaneselenol (CH3SeH) has a higher boiling point than methanethiol (CH3SH).

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) Sulfur forms many molecular compounds with the halogens.

(i) Draw the shape of an SF6 and of an SF4 molecule. Include any lone pairs that influence the shape. State the bond angle(s) in SF6 and in SF4. Name the shape of SF6.

SF6 SF4

Shape

Bond angle(s)

Name of shape

(6)

(ii) SCl2 reacts with NaF to form SF4 and S2Cl2 and one other product.

Write an equation for the reaction.

______________________________________________________________ (2)

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(Total 17 marks)

Q4. Which molecule has the largest dipole?

A ClF3

B BF3

C SF6

D CF4

(Total 1 mark)

Q5. (a) Write an equation, including state symbols, for the reaction with enthalpy change

equal to the standard enthalpy of formation for CF4(g).

___________________________________________________________________ (1)

(b) Explain why CF4 has a bond angle of 109.5°.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) Table 1 gives some values of standard enthalpies of formation (ΔfHϴ).

Table 1

Substance F2(g) CF4(g) HF(g)

ΔfHϴ / kJ mol−1 0 −680 −269

The enthalpy change for the following reaction is −2889 kJ mol−1.

C2H6(g) + 7F2(g) 2CF4(g) + 6HF(g)

Use this value and the standard enthalpies of formation in Table 1 to calculate the standard enthalpy of formation of C2H6(g).

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Standard enthalpy of formation of C2H6(g) = ____________________ kJ mol−1

(3)

(d) Methane reacts violently with fluorine according to the following equation.

CH4(g) + 4F2(g) CF4(g) + 4HF(g) ΔH = −1904 kJ mol−1

Some mean bond enthalpies are given in Table 2.

Table 2

Bond C−H C−F H−F

Mean bond enthalpy / kJ mol−1 412 484 562

A student suggested that one reason for the high reactivity of fluorine is a weak F−F bond.


___________________________________________________________________

___________________________________________________________________ (4)

(Total 10 marks)

Q6. Which substance exists as a macromolecule?

A Cu

B SiO2

C P4O10

D MgO (Total 1 mark)

Q7. Ammonia reacts with aluminium chloride as shown by the equation:

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NH3 + AlCl3 → H3NAlCl3

(a) Draw diagrams to illustrate the shapes of NH3 molecules and of AlCl3 molecules.

Include in your diagrams any lone pairs of electrons that influence the shape.

Indicate the values of the bond angles.

(3)

(b) Name the type of bond formed between N and Al in H3NAlCl3 and explain how this bond is formed.

Type of bond ________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) Explain how the value of the Cl-Al-Cl bond angle in AlCl3 changes, if at all, on formation of the compound H3NAlCl3

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 7 marks)

Q8. Which compound has the highest boiling point?

A C2H4

B C2H6

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C CH3NH2

D CH3F (Total 1 mark)

Q9. Ethanedioic acid is a weak acid. Ethanedioic acid acts, initially, as a monoprotic acid.

(a) Use the concept of electronegativity to justify why the acid strengths of ethanedioic acid and ethanoic acid are different.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(b) A buffer solution is made by adding 6.00 × 10–2 mol of sodium hydroxide to a solution containing 1.00 × 10–1 mol of ethanedioic acid (H2C2O4). Assume that the sodium hydroxide reacts as shown in the following equation and that in this buffer solution, the ethanedioic acid behaves as a monoprotic acid.

H2C2O4(aq) + OH–(aq) HC2O4−(aq) + H2O(l)

The dissociation constant Ka for ethanedioic acid is 5.89 × 10–2 mol dm–3.

Calculate a value for the pH of the buffer solution. Give your answer to the appropriate number of significant figures.

pH = ____________________

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(5)

(c) In a titration, the end point was reached when 25.0 cm3 of an acidified solution containing ethanedioic acid reacted with 20.20 cm3 of 2.00 ×10–2 mol dm–3 potassium manganate(VII) solution.

Deduce an equation for the reaction that occurs and use it to calculate the original concentration of the ethanedioic acid solution.

Equation ___________________________________________________________

Calculation

Original concentration = ____________________ mol dm-3


Q10. The table below contains some entropy data relevant to the reaction used to synthesise methanol from carbon dioxide and hydrogen. The reaction is carried out at a temperature of 250 °C.

Substance CO2(g) H2(g) CH3OH(g) H2O(g)

Entropy (SƟ) / J K−1 mol−1 214 131 238 189

CO2(g) + 3H2(g) CH3OH(g) + H2O(g) ∆H = −49 kJ mol−1

(a) Use this enthalpy change and data from the table to calculate a value for the free-energy change of the reaction at 250 °C. Give units with your answer.

of 46

Free-energy change = _____________ Units = _____________ (4)

(b) Calculate a value for the temperature when the reaction becomes feasible.

Temperature = _______________ K (2)

(c) Gaseous methanol from this reaction is liquefied by cooling before storage.

Draw a diagram showing the interaction between two molecules of methanol. Explain why methanol is easy to liquefy.

Diagram

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 10 marks)

Q11. Which of these substances has permanent dipole-dipole attractions between molecules?

A CCl4

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B C2F4

C (CH3)2CO

D CO2

(Total 1 mark)

Q12. Which type of bond is formed between N and B when a molecule of NH3 reacts with a molecule of BF3?

A Ionic.

B Covalent.

C Co-ordinate.

D Van der Waals. (Total 1 mark)

Q13. (a) Explain how the electron pair repulsion theory can be used to deduce the shape of,

and the bond angle in, PF3

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(b) State the full electron configuration of a cobalt(II) ion.

___________________________________________________________________ (1)

(c) Suggest one reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4]2− ion.

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___________________________________________________________________

___________________________________________________________________ (1)

(d) Predict the shape of, and the bond angle in, the complex rhodium ion [RhCl4]2−.

Shape _____________________________________________________________

Bond angle _________________________________________________________ (2)

(Total 10 marks)

Q14. What is the formula of calcium nitrate(V)?

A CaNO3

B Ca(NO3)2

C Ca2NO2

D Ca(NO2)2

(Total 1 mark)

Q15. Which of these substances does not show hydrogen bonding?

A HF

B NH3

C CH3COOH

D CHF3

(Total 1 mark)

Q16. Which of these atoms has the highest electronegativity?

A Na

B Mg

C Cl

D Ar (Total 1 mark)

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Q17. Use your understanding of intermolecular forces to predict which of these compounds has the highest boiling point.

A HF

B HCl

C HBr

D HI (Total 1 mark)

Q18. Which is the correct crystal structure for the substance named?

Substance Structure

A Iodine Simple molecular

B Diamond Ionic

C Sodium chloride Giant covalent

D Graphite Metallic (Total 1 mark)

Q19. Which of these species has a trigonal planar structure?

A PH3

B BCl3

C H3O+

D CH3−

(Total 1 mark)

Q20. Which statement about intermolecular forces is not correct?

A Intermolecular forces exist between all simple

molecules.

B Hydrogen bonding occurs between HBr molecules.

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C Hydrogen bonding is the strongest intermolecular force in liquid ethanol.

D Hydrogen bonds occur between C=O and H−N in proteins.

(Total 1 mark)

Q21. Which molecule is the least polar?

A Bromomethane

B Dibromomethane

C Tribromomethane

D Tetrabromomethane (Total 1 mark)

Q22. Which of these statements best describes a dative covalent bond?

A A pair of electrons shared between two atoms

where each atom has donated one electron.

B A pair of electrons shared between two atoms where one atom has donated two electrons.

C Two pairs of electrons shared between two atoms where each atom has donated one electron.

D Two pairs of electrons shared between two atoms where each atom has donated two electrons.

(Total 1 mark)

Q23. This question is about the chemistry of some Group 2 elements.

(a) Write an equation for the reaction of calcium with water at 25 °C and predict a possible value for the pH of the solution formed.

Equation

___________________________________________________________________

pH ________________________________________________________________ (2)

(b) State the trend in solubility, in water, of the Group 2 sulfates from magnesium to barium.

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___________________________________________________________________ (1)

(c) State the trend in solubility, in water, of the Group 2 sulfates from magnesium to barium.

Reagent ___________________________________________________________

Equation

___________________________________________________________________ (2)

(d) Explain why the melting point of calcium sulfate is high.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 7 marks)

Q24. Which molecule does not have a permanent dipole?

A CH3Cl

B CHCl3

C CF4

D CHCl2F (Total 1 mark)

Q25. This question is about the element iodine and its compounds.

(a) Iodine is in Group 7 of the Periodic Table.

Complete the electron configuration of an iodine atom.

[Kr] ________________________________________________________________ (1)

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(b) Part of the structure of an iodine crystal is shown in the diagram.

Use your knowledge of structure and bonding to explain why the melting point of iodine is low (113.5 °C) and why that of hydrogen iodide is very low (–50.8 °C).

(6)

(c) State why iodine does not conduct electricity.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(d) Deduce an equation for the formation of hydrogen iodide from its elements.

___________________________________________________________________ (1)

(e) The triiodide ion is formed when an iodine molecule is bonded to an iodide ion.

What is the formula of ammonium triiodide?

Tick (✔) one box.

NH3I3

NH3I4

NH4I

NH4I3

(1)

(f) Draw the shape of the IF3 molecule and the shape of the IF4− ion. Include any lone pairs of electrons that influence each shape.

of 46

(2)

(g) Deduce the oxidation state of iodine in the following species.

Ba(IO3)2 _____________________________________________________________

[H4IO6]− _____________________________________________________________


Q26. Which of these species is not planar?

A HCHO

B CH3+

C CH3OH

D C2H4

(Total 1 mark)

Q27. Halogenoalkanes such as 1,1,2-trichloro-1,2,2-trifluoroethane were used as coolants in refrigerators until the late 1980s. Their use was then banned and alternative coolants were used instead.

(a) Draw the displayed formula of 1,1,2-trichloro-1,2,2-trifluoroethane.

(1)

(b) 1,1,2-Trichloro-1,2,2-trifluoroethane was banned for use as a refrigerant because it damaged the ozone layer.

Write three equations to show how this compound is involved in damaging the ozone layer.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

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(c) State the role of chlorine atoms in the reactions in part (b).

___________________________________________________________________ (1)

(d) Inevitably, some coolant escapes from refrigerators.

Deduce which of the following coolants, A, B or C, would cause least environmental damage to the atmosphere.

CHCl2CHClF CF3CH2F CF3CCl2F

A B C

Coolant ________ (1)

(e) Give the IUPAC name of compound B in part (d).

___________________________________________________________________ (1)

(f) The boiling point of iodomethane (CH3I) is higher than that of fluoromethane (CH3F) even though the electronegativity of iodine is less than that of fluorine.

Explain why iodomethane has the higher boiling point by considering the forces that act between CH3I molecules and comparing these forces with the forces between the CH3F molecules.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 10 marks)

Q28. Which compound has the highest boiling point?

A CH3CH2CH2OH

B CH3CH2CHO

C CH3COCH3

D CH3COOCH3

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(Total 1 mark)

Q29. This question is about elements in Group 7 of the Periodic Table and their compounds.

(a) Bromine (Br2), strontium chloride (SrCl2) and iodine monochloride (ICl) all have similar Mr values.

Suggest, with reasons, the order of melting points for these three substances. (6)

(b) Write an equation for the reaction of chlorine with cold water.

State a reason why chlorine is added to drinking water, and suggest a disadvantage of treating water in this way.

Equation

___________________________________________________________________

Reason ____________________________________________________________

___________________________________________________________________

Disadvantage _______________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) Bromine reacts with phosphorus to form phosphorus tribromide.

Write an equation for this reaction and draw the shape of the phosphorus tribromide molecule formed.

Suggest the bond angle in phosphorus tribromide.

Equation

___________________________________________________________________

Shape

Bond angle _________________________________________________________ (3)

(d) Phosphorus pentabromide in the solid state consists of PBr4+ and Br − ions.

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Draw the shape of the PBr4+ ion and suggest its bond angle.

Shape

Bond angle _________________________________________________________ (2)

(Total 14 marks)

Q30. This question is about intermolecular forces.

(a) Give the meaning of the term electronegativity.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(b) Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) Complete the table by naming the shape of each molecule.

Place a tick (✔) in the final column if the molecule has a permanent dipole.

Molecule Name of shape Tick (✔) if molecule has a permanent dipole

SiH4

PH3

BeCl2

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CH3Cl

(4) (Total 7 marks)

Q31. This question is about some Period 3 elements and their oxides.

(a) Write an equation for the reaction of phosphorus with an excess of oxygen.

___________________________________________________________________ (1)

(b) Describe a test you could carry out in a test tube to distinguish between sodium oxide and the product of the reaction in part (a)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) State the type of crystal structure shown in silicon dioxide and in sulfur trioxide.

Silicon dioxide _______________________________________________________

Sulfur trioxide _______________________________________________________ (2)

(d) Explain why silicon dioxide has a higher melting point than sulfur trioxide.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(e) Write an equation for the reaction of sulfur trioxide with potassium hydroxide solution.

of 46

___________________________________________________________________

___________________________________________________________________ (1)

(f) Write an equation for the reaction of an excess of magnesium oxide with phosphoric acid.

___________________________________________________________________

___________________________________________________________________ (1)

(g) Draw the displayed formula of the undissociated acid formed when sulfur dioxide reacts with water.

(1)

(Total 13 marks)

Q32. Which is the most likely bond angle around the oxygen atom in ethanol?

A 104.5°

B 109.5°

C 120°

D 180° (Total 1 mark)

Q33. Which species has one or more bond angle(s) of 90°?

A CH4

B NH4+

C ClF4−

D AlCl4−

(Total 1 mark)

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Q34. Alcohols undergo dehydration in the presence of concentrated phosphoric acid, via a carbocation intermediate, to form alkenes.

(a) Complete the mechanism for the conversion of 2-methylcyclohexanol into 1-methylcyclohexene via carbocation D by drawing

• the structure of the missing intermediate • all necessary curly arrows.

(4)

(b) Draw the structure of a different cyclic alkene formed from carbocation D.

(1)

(c) Carbocation D can undergo a type of reaction called a rearrangement to form carbocation E. In this reaction, a hydrogen atom and its bonding pair of electrons move from carbon a to carbon b as shown in the diagram below.

of 46

Use your knowledge of carbocations to explain why this rearrangement takes place.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) As a result of the rearrangement in part (c), a third alkene is formed in this reaction.

Draw the structure of this third alkene.

(1)

(e) Cyclohexene is prepared by the dehydration of cyclohexanol using concentrated phosphoric acid as a catalyst. The structure of concentrated phosphoric acid is shown.

Identify the factors that influence the boiling points of each of the compounds in this reaction mixture. State how and explain why cyclohexene can be separated from the reaction mixture.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(Total 14 marks)

Q35. Chloroethene can be polymerised to form poly(chloroethene), commonly known as PVC. This polymer can be used to make pipes, window frames and electrical insulation. Plasticisers can be added to change the properties of PVC

A section of poly(chloroethene) is shown.

(a) Chloroethene has a melting point of −154 °C

All types of PVC melt at temperatures over 100 °C

Explain why PVC melts at a higher temperature than chloroethene.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) This structure shows a molecule that has been used as a plasticiser in PVC.

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Deduce the number of hydrogen atoms in this molecule.

___________________________________________________________________ (1)

(c) Use your understanding of the properties of PVC to explain whether you would expect to find a plasticiser in the PVC used to insulate electrical cables.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(d) A section of the polymer poly(chloroprene), a synthetic rubber, is shown.

Draw the displayed formula for the repeating unit of poly(chloroprene).

(1)

(Total 5 marks)

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Mark schemes

Q1. (a) General increase

If not increase then CE 1

Greater nuclear charge / more protons 1

Same shielding / electrons added to same shell Allow similar

1 Stronger attraction (from nucleus) for outer electron(s)

Allow electron in outer shell 1

(b) Aluminium / Al (lower than Mg) CE if not Al or S

1 (Outer) electron in (3)p orbital / sub-shell (level)

If 2p or 4p orbital lose M2 and M3 1

(3p) higher in energy Allow more shielded or weaker nuclear attraction M3 is dependent on M2

1 or Sulfur / S (lower than P) (Outer) electrons in (3)p orbital begin to pair Repel

If 2p or 4p orbital lose M2 and M3 Allow 2 electrons in (3)p M3 is dependent on M2

(c) Sulfur / S CE if not S

1 Large jump after 6th or between 6th and 7th

Do not allow M2 if atom/ion is removed 1

(d) Silicon CE if not Si

1 Giant covalent structure / macromolecule

1 Covalent (bonds)

Giant covalent scores M2 and M3 1

Many / strong (covalent bonds) or (covalent bonds) need lots of energy to break

CE for M2-M4 if molecules / metallic / ionic / IMFs mentioned 1

[13]

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Q2. Structures M1 Bromine is (simple) molecular / simple molecules

Chemical Error penalties 1

M2 Magnesium is metallic / consists of (positive) ions in a (sea) of delocalised electrons

If Br2 (covalent) bonds broken lose M3 and M4 1

Strength M3 Br2 has weak (van der Waals) forces between the molecules / weak IMFs

If eg Mg molecules or Mg ionic bonds lose M2 and M4 1

M4 so more energy is needed to overcome the Stronger (metallic) bonds or converse. The comparison could be direct or implied.

1

Liquid range M5 Mg has a much greater liquid range because forces of attraction in liquid / molten metal are strong(er) OR converse argument for Br2

Must refer to liquid range to score M5 1

[5]

Q3. (a) Electron movement in first molecule / temporary dipole

Allow description 1

Induces a dipole in another molecule Allow description

1 (Induced-temporary) attraction or δ+ attracts δ- in different/adjacent molecules

M3 dependent on M1 and M2 Allow electrostatic attraction M3 could be scored in diagram If other type of force / metallic / ionic / polar bonds / permanent dipoles / difference in electronegativity mentioned CE = 0

1

(b) (i) (Methanol) H-bonds / hydrogen bonding 1

(Methanethiol) dipole-dipole forces or van der Waals 1

H-bonds are a stronger / are the strongest IMF Allow H-bonds require more energy to overcome If M1 and M2 not scored, allow 1 for methanol has stronger IMFs If breaking covalent bonds then CE=0

1

(ii) (Fractional) distillation Allow description Do not allow heating unqualified

1

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(c) (Methaneselenol is a) bigger molecule / larger Mr / larger no of electrons / Se bigger atom

1 With stronger/more vdw forces between molecules

If breaking covalent bonds then CE=0 1

(d) (i) Diagram showing 6 bond pairs

1 (Bond angle) 90° for SF6

Ignore 180° 1

Octahedral 1

Diagram showing 4 bond pairs and 1 lone pair

1 (Bond angles) for SF4

If shape of SF4 is not based on 4 bond pairs and 1 lone pair cannot score M4 or M5

Any two from: Allow 85 – 89°

Do not allow 90° Allow 100 – 119°

Do not allow 120° Allow 170 – 179°

Do not allow 180° 2

(ii) NaCl (as product in any equation) 1

3 SCI2 + 4 NaF → SF4 + S2Cl2 + 4 NaCl Allow multiples Ignore states

1 [17]

Q4. A

[1]

Q5. (a) C(s) + 2F2(g) CF4(g)

State symbols essential 1

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(b) Around carbon there are 4 bonding pairs of electrons (and no lone pairs) 1

Therefore, these repel equally and spread as far apart as possible 1

(c) ΔH = Σ ΔfH products – Σ ΔfH reactants or a correct cycle 1

Hence = (2 × –680) + (6 × –269) – (x) = –2889 1

x = 2889 – 1360 – 1614 = –85 (kJ mol–1) 1

Score 1 mark only for +85 (kJ mol–1)

(d) Bonds broken = 4(C–H) + 4(F–F) = 4 × 412 + 4 × F–F

Bonds formed = 4(C–F) + 4(H–F) = 4 × 484 + 4 × 562 Both required

1

–1904 = [4 × 412 + 4(F–F)] – [4 × 484 + 4 × 562]

4(F–F) = –1904 – 4 × 412 + [4 × 484 + 4 × 562] = 632 1

F–F = 632 / 4 = 158 (kJ mol–1) 1

The student is correct because the F–F bond energy is much less than the C–H or other covalent bonds, therefore the F–F bond is weak / easily broken

Relevant comment comparing to other bonds (Low activation energy needed to break the F–F bond)

1 [10]

Q6. B

[1]

Q7. (a) Correct diagram of NH3 including LP on N

1 Correct diagram of AlCl3

1 Bond angles in range 106-108° and bond angle of 120°

1

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Ignore shape names

(b) Dative (covalent) /co-ordinate bond Wrong bond CE=0 but mark on if covalent quoted

1

Shared pair of / both electrons come from the N(H3) 1

(c) Aluminium is now surrounded by 4 electron pairs/bonds or is tetrahedral Independent

1

Therefore Cl-Al-Cl bond angle decreases / changes (from 120° in AlCl3 ) to allow range 107-111° in H3NAlCl3

1 [7]

Q8. C

[1]

Q9. (a) This question is marked using levels of response. Refer to the Mark Scheme

Instructions for Examiners for guidance on how to mark this question.


Answer is communicated coherently and shows a logical progression from stage 1 and stage 2 to stage 3. Steps in stage 3 must be complete, ordered and include a comparison.

Level 3 5 – 6 marks


Answer is mainly coherent and shows a progression from stage 1 and stage 2 to stage 3.



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Insufficient correct Chemistry to warrant a mark. Level 0

0 marks

Indicative Chemistry content

Stage 1: difference in structure of the two acids • The acids are of the form RCOOH • but in ethanoic acid R = CH3

• whilst in ethanedioic acid R = COOH

Stage 2: the inductive effect • The unionised COOH group contains two very electronegative oxygen

atoms • therefore has a negative inductive (electron withdrawing)effect • The CH3 group has a positive inductive (electron pushing) effect

Stage 3: how the polarity of OH affects acid strength • The O–H bond in the ethanedioic acid is more polarised / H becomes

more δ+

• More dissociation into H+ ions • Ethanedioic acid is stronger than ethanoic acid

6

(b) Moles of NaOH = Moles of HOOCCOO– formed = 6.00 × 10–2

Extended response 1

Moles of HOOCCOOH remaining = 1.00 × 10–1 – 6.00 × 10–2

= 4.00 × 10–2

1

Ka = [H+][A–] / [HA]

[H+] = Ka × [HA] / [A–] 1

[H+] = 5.89 × 10–2 × (4.00 × 10–2 / V) / (6.00 × 10–2 / V) = 3.927 × 10–2

1

pH = –log10(3.927 ×10–2) = 1.406 = 1.41 Answer must be given to this precision

1

(c) 5H2C2O4 + 6H+ + 2MnO4– 2Mn2+ + 10CO2 + 8H2O

OR 5C2O42– + 16H+ + 2MnO4– 2Mn2+ + 10CO2 + 8H2O 1

Moles of KMnO4 = 20.2 × 2.00 × 10–2 / 1000 = 4.04 × 10–4

1

Moles of H2C2O4 = 5 / 2 × 4.04 × 10–4 = 1.01 × 10–3

1

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Concentration = moles / volume (in dm3)

= 1.01 × 10–3 × 1000 / 25 = 4.04 × 10–2 (mol dm–3) If 1:1 ratio or incorrect ratio used, M2 and M4 can be scored

1 [15]

Q10. (a) ΔS = 238 + 189 – 214 – 3 × 131 = –180 J K–1 mol–1

1

ΔG = ΔH – TΔS 1

= –49 – 1

= +45.1 kJ mol–1

Units essential 1

(b) When ΔG = 0, ΔH = TΔS therefore T = ΔH / ΔS 1

= –49 × 1000 / –180 = 272 (K) Mark consequentially to ΔS in part (a)

1

(c) Diagram marks

Diagram of a molecule showing O–H bond and two lone pairs on each oxygen 1

Labels on diagram showing δ+ and δ- charges Allow explanation of position of δ+ and δ- charges on H and O

1

Diagram showing δ+ hydrogen on one molecule attracted to lone pair on a second molecule

1

Explanation mark

Hydrogen bonding (the name mentioned) is a strong enough force (to hold methanol molecules together in a liquid)

1 [10]

Q11.

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C [1]

Q12. C

[1]




Answer is communicated coherently and shows a logical progression from stage 1 to stage 2 then stage 3.



Answer is mainly coherent and shows progression from stage 1 to stage 3. Level 2

3 – 4 marks

Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete



Insufficient correct chemistry to gain a mark. Level 0

0 marks

Indicative chemistry content

Stage 1: Electrons round P • P has 5 electrons in the outside shell • With 3 electrons from 3 fluorine, there are a total of 8 electrons in outside

shell • so 3 bond pairs, 1 non-bond pair

Stage 2: Electron pair repulsion theory • Electron pairs repel as far as possible • Lone pair repels more than bonding pairs

Stage 3: Conclusions • Therefore, tetrahedral / trigonal pyramidal shape • With angle of 109(.5)° decreased to 107°

6

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(b) 1s22s22p63s23p63d7

Allow correct numbers that are not superscripted 1

(c) Too many electrons in d sub-shell / orbitals 1

(d) Tetrahedral (shape) 1

109.5° Allow 109°

1 [10]

Q14. B

[1]

Q15. D

[1]

Q16. C

[1]

Q17. A

[1]

Q18. A

[1]

Q19. B

[1]

Q20. B

[1]

Q21. D

[1]

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Q22. B

[1]

Q23. (a) Ca + 2H2O ⟶ Ca(OH)2 + H2

1

8 − 12 1

(b) Decrease 1

(c) BaCl2

Allow Ba(NO3)2 or other soluble barium salt 1

Ba2+ + SO42− ⟶ BaSO4

Allow equation if state symbols missing but penalise if state symbols are incorrect

1

(d) Strong attraction 1

Between positive and negative ions 1

[7]

Q24. C

[1]

Q25. (a) [Kr] 5s2 4d105p5

1

(b) This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question.

Level 3 All stages are covered and the explanation of each stage is correct and complete.

Answer communicates the whole explanation coherently and shows a logical progression from stage 1 to stage 2 and then stage 3.

5-6 marks

Level 2 All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete.

Answer is mainly coherent and shows a progression through the stages. Some steps in each stage may be out of order and incomplete.

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3-4 marks

Level 1 Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete.


1-2 marks

Level 0 Insufficient correct chemistry to warrant a mark.

0 marks

Indicative Chemistry content Stage 1 I2 is molecular. HI is molecular. Stage 2 IMF hold the molecules together. There are weak IMF forces hence the melting point is low in both substances. I2 bigger molecule than HI so I2 has more electrons. Stage 3 Therefore stronger van der Waals between molecules in I2 that need more energy to break causing the melting point to be higher. HI also shows permanent dipole-dipole attraction between molecules but these forces are less than the vdW forces in iodine.

6

(c) No delocalised electrons or ions 1

(d) ⟶ HI Allow multiples

1

(e) NH4I3 1

(f) Allow any shape with 3 bond pairs and 2 lone pairs

1

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Allow any shape with 4 bond pairs and 2 lone pairs (e.g. lone pairs in equatorial positions)

1

(g) +5 1

+7 1

[14]

Q26. C

[1]

Q27. (a)

1

(b) Initiation: CCl2FCF2Cl ⟶ Cl• + CCl2FCF2.

Allow initiation equations where more than one Cl• is formed 1

Cl• + O3 ⟶ ClO• + O2 1

ClO• + O3 ⟶ 2O2 + Cl• 1

(c) Acts as a catalyst 1

(d) B 1

(e) 1,1,1,2-tetrafluoroethane 1

(f) Iodine is bigger than fluorine so the van der Waals forces between CH3I molecules

of 46

are stronger than those between CH3F molecules 1

The dipole-dipole forces between CH3F molecules are stronger than those between CH3I molecules

Or vice versa 1

The van der Waals forces are stronger than the dipole-dipole forces so these dominate

1 [10]

Q28. A

[1]

Q29. (a) SrCl2> ICl > Br>

If wrong can award 1 for one in the correct ‘position’ 2

SrCl2 strong ionic bonds / (strong electrostatic attraction between opposite ions) 1

Lattice so many strong bonds to overcome 1

ICl has dipole-dipole between molecules – weaker than ionic bonds 1

Br2 has van der Waals forces between molecules – much weaker Accept London / dispersion / induced dipole forces

1

(b) Cl2 + H2O ⇌ HCl + HClO OR 2Cl2 + 2H2O ⇌ O2 + 4HCl OR Cl2 + H2O ⇌ 2H+ + Cl− + ClO−

1

Kills bacteria 1

Wasteful as most potable water not used for drinking - used in washing clothes etc

OR Some people suffer eye irritation / Some people find the taste unpleasant

OR can react with organic compounds to produce harmful substances Allow ‘it is potentially toxic as it can be if over concentrated’

1

(c) 6Br2 + P4 ⟶ 4PBr3

Accept 4P for P4 1

Pyramidal shown in a diagram (but the name of the shape isn’t needed)

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1

100–108° Actual value is 101° (hence larger range of values allowed)

1

(d) Tetrahedral shown in a diagram (but the name of the shape isn’t needed) 1

109.5° Accept 109° or 109°28’

1 [14]

Q30. (a) Power of an atom to attract a pair of electrons in a covalent bond.

Allow power of an atom to attract a bonding/shared pair of electrons Allow power of an atom to withdraw electron density from a covalent bond Not lone pair Not Element

1

(b) Difference in electronegativity leads to bond polarity If chloride (ions) mentioned then CE = 0

1

(dipoles don’t cancel therefore the molecule has an overall permanent dipole) and there is an attraction between ∂+ on one molecule and ∂− on another

partial charges should be correct if shown and can score M2 from diagram

1

(c)

SiH4 Tetrahedral 1 shape & no tick

PH3 Pyramidal (trigonal) Allow tetrahedral ✓ 1 shape &

tick

BeCl2 Linear 1 shape & no tick

CH3Cl (Distorted)Tetrahedral ✓ 1 shape & tick

If shapes are drawn rather than named then penalise first mark gained 4

[7]

Q31. (a) P4 + 5 O2 → P4O10

allow 4 P + 5 O2 → P4O10

allow multiples

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ignore state symbols 1

(b) React with water / add water / solution (of substances in question) If no M1 then CE = 0/3

1

Add litmus paper / universal indicator / measure pH (with pH meter) Allow other reagents in solution, e.g. sodium carbonate solution, that give a positive result Allow other indicators with appropriate colour changes

1

M3 is dependent on M2 Litmus: blue with sodium oxide (solution) and red with phosphorus oxide (solution)OR If blue litmus added phosphorus oxide solution goes red OR If red litmus added sodium (hydr)oxide goes blue

Universal Indicator: blue/ purple with sodium oxide (solution) and red with phosphorus oxide (solution)

pH meter or Universal Indicator: sodium (hydr)oxide (solution) has a higher pH (than phosphorus oxide (solution)) or vv

sodium (hydr)oxide pH (12 to 14) and phosphorus oxide (solution) pH (-1 to 2) For pH meter or Universal Indicator: allow sodium (hydr)oxide (solution) has a higher pH and phosphorus oxide (solution) has lower pH.

1

(c) For silicon dioxide - giant covalent (molecule)/ macromolecular 1

For sulfur trioxide - molecular / (simple) molecule 1

Do not allow simple covalent

(d) Covalent bonds (between atoms) in SiO2 1

Van der Waals between molecules / intermolecular forces in SO3 1

Covalent bonds are stronger than van der Waals forces 1

(Covalent bonds) take more energy to be overcome/broken or (Van der Waals) take less energy to be overcome/broken

1

If covalent bonds between molecules of SiO2 lose M1 only If hydrogen bonds in SO3 lose M2 only If metallic or ionic max score = 1 (either M1 or M2) If IMF in SiO2 then max 1 ( M2 only) Allow dipole-dipole forces between molecules For M3 and M4 comparison is required/implied

(e) SO3 + 2KOH → K2SO4 + H2O

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SO3 + KOH → KHSO4

SO3 + 2OH− → SO42−+ H2O SO3 + OH− → HSO4−

Allow multiples Ignore state symbols

1

(f) 3 MgO + 2 H3PO4 → Mg3(PO4)2 + 3 H2O Allow multiples Ignore state symbols

1

(g) Ignore lone pairs

1 [13]

Q32. A

[1]

Q33. C

[1]

Q34. (a)

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M1 curly arrow from lone pair on O to H+

1

M2 correct structure of intermediate with + on O 1

M3 curly arrow from C‑O bond to O 1

M4 curly arrow from correct C‑H bond towards correct C‑C bond 1

Ignore other species that are drawn, but penalise any curly arrows to/from other species for M1/3/4 as relevant (but allow attack by an anion of phosphoric acid on the H that is lost in M4 in addition to the arrow specified) for M2, the O of the +OH2 group must be bonded to the ring

(b)

Any correct structural representation 1

(c) M1 more stable (carbocation formed) For M1 penalise more stable product

1

M2 changes from secondary to tertiary (carbocation) For M2 allow explanation via inductive effect with more alkyl /

of 46

C groups attached or inductive effect from methyl group as alternatives Allow 2o or 2y for secondary and 3o or 3y for tertiary

1

(d)

Any correct structural representation

1

(e) M1 cyclohexene : van der Waals’ forces (between molecules) 1

M2 cyclohexanol : hydrogen bonds (between molecules) 1

M3 phosphoric acid: hydrogen bonds (between molecules) 1

M4 idea that cyclohexene has weakest forces 1

M5 separated by (simple / fractional) distillation 1

M6 cyclohexene has lowest boiling point / boils off first Extended response Maximum of 5 marks for answers which do not refer to the van der Waals forces or hydrogen bonds being between molecules in some way M1 penalise reference to presence of other intermolecular forces M1 allow vdW forces (on this occasion) M1/2/3 penalise reference to breaking covalent bonds M2 & M3 ignore reference to van der Waals and/or (permanent) dipole-dipole forces M2 allow use of term H bonds (on this occasion) M4 allow converse argument M4 & M6 – allow correct comparison of cyclohexene forces and boiling point to one of the other two compounds if only one of cyclohexanol or phosphoric acid discussed

[14]

Q35. (a) M1 it / PVC is bigger/longer molecule / has more electrons / has bigger

surface area / greater Mr 1

M2 it / PVC has stronger (van der Waals’ / dipole-dipole) forces between molecules / intermolecular forces

1

M1 and M2 independent of each other CE = 0 if reference to hydrogen bonds or breaking of covalent

of 46

bonds when substances are melted Comparison must be implied in M1 or M2 to score 2 marks If there is no comparison at all, then 1 mark could score either for explaining that PVC has strong intermolecular forces due to being a big/long molecule / having many electrons / large surface area / large Mr , or, for explaining that chloroethene has weak intermolecular forces due to being a small/short molecule / having few electrons / low surface area / low Mr ,

(b) 38

ignore additional words 1

(c) Need both ideas that

• it is present AND • because PVC needs to be flexible / bendy

penalise incorrect properties 1

(d) Displayed structure required

ignore any bracket or n

1 [5]

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Energetics exam pack 1

Name: ________________________

Class: ________________________

Date: ________________________

Time: 397 minutes

Marks: 347 marks

Comments:

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Q1. A student calculated that a value for the enthalpy change of neutralisation is –51.2 kJ mol–1.

The design of a possible hand-warmer using hydrochloric acid and sodium hydroxide was discussed. It was proposed that 500 cm3 of hydrochloric acid should be used in a flexible, sealed plastic container with a breakable tube of solid sodium hydroxide also in the container. On breaking the tube, the sodium hydroxide would be released, react with the acid and produce heat. A 40 °C temperature rise was thought to be suitable.

(a) Calculate the heat energy, in J, required to raise the temperature of the reaction mixture by 40 °C. Assume that the reaction mixture has a density of 1.00 g cm–3 and a specific heat capacity of 4.18 J K–1 g–1. Assume that all of the heat energy given out is used to heat the reaction mixture.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) Use your answer from part (a) and the value for the enthalpy change of neutralisation of –51.2 kJ mol–1 to calculate the minimum amount, in moles, and hence the minimum mass of sodium hydroxide required in the breakable tube. (If you could not complete the calculation in part (a) assume that the heat energy required was 77 400 J. This is not the correct answer).

Show your working.

Moles of NaOH ______________________________________________________

___________________________________________________________________

Mass of NaOH ______________________________________________________

___________________________________________________________________ (3)

(c) Use the amount, in moles, of sodium hydroxide from part (b) to calculate the minimum concentration, in mol dm–3, of hydrochloric acid required in the 500 cm3 of solution used in the sealed container.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(d) Suggest one possible risk to a person who uses a hand-warmer containing sodium hydroxide and hydrochloric acid.

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___________________________________________________________________

___________________________________________________________________ (1)

(e) A commercial hand-warmer uses powdered iron sealed in a plastic container. A valve allows air to enter the container, and oxygen in the air reacts slowly with the iron to form solid iron(lll) oxide. The heat released warms the container.

(i) Write an equation for this reaction between iron and oxygen to form iron(lll) oxide.

______________________________________________________________ (1)

(ii) One version of an iron-oxygen hand-warmer advertises that it is designed to stay warm for up to four hours. Other than by increasing the amount of iron in the container, state one change to the iron in the hand-warmer that would increase this time. Explain why this change to the iron might not be an advantage.

Change to the iron ______________________________________________

______________________________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(f) Another type of hand-warmer uses sodium thiosulfate. Sodium thiosulfate is very soluble in water at 80 °C but is much less soluble at room temperature. When a hot, concentrated solution of sodium thiosulfate is cooled it does not immediately crystallise. The sodium thiosulfate stays dissolved as a stable ’super-saturated’ solution until crystallisation is triggered. Heat energy is then released when the sodium thiosulfate crystallises.

(i) This type of hand-warmer is re-usable. Suggest one environmental advantage that a sodium thiosulfate hand-warmer has over the other two types.

______________________________________________________________ (1)

(ii) Describe the two steps that you would take to make the sodium thiosulfate hand-warmer ready for re-use.

Step 1 ________________________________________________________

______________________________________________________________

Step 2 ________________________________________________________

______________________________________________________________ (2)

(Total 14 marks)

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Q2. The table shows the standard enthalpy of formation, ΔfHθ, for some of the substances in the reaction

C2H6(g) + 6F2(g) ⟶ C2F6(g) + 6HF(g) ΔHθ = −2898 kJ mol−1

C2H6(g) C2F6(g)

ΔfHθ /kJ mol−1 −84 −1344

What is the standard enthalpy of formation, in kJ mol−1, for HF(g)?

A −1638

B −273

C +273

D +1638 (Total 1 mark)

Q3. (a) Anhydrous calcium chloride is not used as a commercial de-icer because it reacts

with water. The reaction with water is exothermic and causes handling problems.

A student weighed out 1.00 g of anhydrous calcium chloride. Using a pipette, 25.0 cm3 of water were measured out and transferred to a plastic cup. The cup was placed in a beaker to provide insulation. A thermometer was mounted in the cup using a clamp and stand. The bulb of the thermometer was fully immersed in the water.

The student recorded the temperature of the water in the cup every minute, stirring the water before reading the temperature. At the fourth minute the anhydrous calcium chloride was added, but the temperature was not recorded. The mixture was stirred, then the temperature was recorded at the fifth minute. The student continued stirring and recording the temperature at minute intervals for seven more minutes.

The student’s results are shown in the table below.

Time / minutes 0 1 2 3 4

Temperature / °C 19.6 19.5 19.5 19.5

Time / minutes 4 5 6 7 8 9 10 11 12

Temperature / °C 24.6 25.0 25.2 24.7 24.6 23.9 23.4 23.0

Plot a graph of temperature (y-axis) against time on the grid below. Draw a line of best fit for the points before the fourth minute. Draw a second line of best fit for the appropriate points after the fourth minute. Extrapolate both lines to the fourth minute.

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(5)

(b) Use your graph to determine an accurate value for the temperature of the water at the fourth minute (before mixing).

Temperature before mixing ____________________________________________ (1)

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(c) Use your graph to determine an accurate value for the temperature of the reaction mixture at the fourth minute (after mixing).

Temperature after mixing ______________________________________________ (1)

(d) Use your answers from parts (b) and (c) to determine an accurate value for the temperature rise at the fourth minute. Give your answer to the appropriate precision.

Temperature rise ____________________________________________________ (1)

(e) Use your answer from part (d) to calculate the heat given out during this experiment. Assume that the water has a density of 1.00 g cm–3 and a specific heat capacity of 4.18 JK–1 g–1. Assume that all of the heat given out is used to heat the water. Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(f) Calculate the amount, in moles, of CaCl2 in 1.00 g of anhydrous calcium chloride (Mr = 111.0).

___________________________________________________________________ (1)

(g) Use your answers from parts (e) and (f) to calculate a value for the enthalpy change, in kJ mol–1, for the reaction that occurs when anhydrous calcium chloride dissolves in water.

CaCl2(s) + aq CaCl2(aq)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(h) Explain why it is important that the reaction mixture is stirred before recording each temperature.

___________________________________________________________________

___________________________________________________________________ (1)

(i) Anhydrous calcium chloride can be prepared by passing chlorine over heated calcium.

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To prevent unreacted chlorine escaping into the atmosphere, a student suggested the diagram of the apparatus for this experiment shown below.

(i) Suggest one reason why the student wished to prevent unreacted chlorine escaping into the atmosphere.

______________________________________________________________

______________________________________________________________ (1)

(ii) Suggest one hazard of using the apparatus as suggested by the student for this experiment.

______________________________________________________________

______________________________________________________________ (1)

(Total 16 marks)

Q4. Methanol (CH3OH) is an important fuel that can be synthesised from carbon dioxide.

(a) The table shows some standard enthalpies of formation.

CO2(g) H2(g) CH3OH(g) H2O(g)

∆HfƟ/kJ mol–1 – 394 0 – 201 – 242

(i) Use these standard enthalpies of formation to calculate a value for the standard enthalpy change of this synthesis.

CO2(g) + 3H2(g)

CH3OH(g) + H2O(g)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

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______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) State why the standard enthalpy of formation for hydrogen gas is zero.

______________________________________________________________

______________________________________________________________ (1)

(b) State and explain what happens to the yield of methanol when the total pressure is increased in this synthesis.

CO2(g) + 3H2(g)

CH3OH(g) + H2O(g)

Effect on yield _______________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(c) The hydrogen required for this synthesis is formed from methane and steam in a reversible reaction. The equation for this reaction is shown below.

CH4(g) + H2O(g) C0(g) + 3H2(g) ∆H = +206 kJ mol–1

State and explain what happens to the yield of hydrogen in this reaction when the temperature is increased.

Effect on yield _______________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(d) The methanol produced by this synthesis has been described as a carbon-neutral fuel.


______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (1)

(ii) Write an equation for the complete combustion of methanol.

______________________________________________________________ (1)

(iii) The equation for the synthesis of methanol is shown below.

CO2(g) + 3H2(g)

CH3OH(g) + H2O(g)

Use this equation and your answer to part (d)(ii) to deduce an equation to represent the overall chemical change that occurs when methanol behaves as a carbon-neutral fuel.

Equation ___________________________________________________ (1)

(e) A student carried out an experiment to determine the enthalpy change when a sample of methanol was burned.

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The student found that the temperature of 140 g of water increased by 7.5 °C when 0.011 mol of methanol was burned in air and the heat produced was used to warm the water.

Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of methanol was burned. (The specific heat capacity of water is 4.18 J K–1 g–1).

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(Total 16 marks)

Q5. This question is about bond dissociation enthalpies and their use in the calculation of enthalpy changes.

(a) Define bond dissociation enthalpy as applied to chlorine.

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(b) Explain why the enthalpy of atomisation of chlorine is exactly half the bond dissociation enthalpy of chlorine.

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(1)

(c) The bond dissociation enthalpy for chlorine is +242 kJ mol−1 and that for fluorine is +158 kJ mol−1. The standard enthalpy of formation of ClF(g) is −56 kJ mol−1.

(i) Write an equation, including state symbols, for the reaction that has an enthalpy change equal to the standard enthalpy of formation of gaseous ClF

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(ii) Calculate a value for the bond enthalpy of the Cl – F bond.

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(iii) Calculate the enthalpy of formation of gaseous chlorine trifluoride, ClF3(g). Use the bond enthalpy value that you obtained in part (c)(ii).

(If you have been unable to obtain an answer to part (c)(ii), you may assume that the Cl – F bond enthalpy is +223 kJ mol−1. This is not the correct value.)

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(iv) Explain why the enthalpy of formation of ClF3(g) that you calculated in part (c)(iii) is likely to be different from a data book value.

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(d) Suggest why a value for the Na – Cl bond enthalpy is not found in any data book.

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Q6. Group 2 metals and their compounds are used commercially in a variety of processes.

(a) Strontium is extracted from strontium oxide (SrO) by heating a mixture of powdered strontium oxide and powdered aluminium.

Consider these standard enthalpies of formation.

SrO(s) Al2O3(s)

ΔHfϴ / kJ mol−1 – 590 – 1669

3SrO(s) + 2Al(s) 3Sr(s) + Al2O3(s)

Use these data and the equation to calculate the standard enthalpy change for this extraction of strontium.

The use of powdered strontium oxide and powdered aluminium increases the surface area of the reactants. Suggest one reason why this increases the reaction rate.

Suggest one major reason why this method of extracting strontium is expensive.

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(b) Explain why calcium has a higher melting point than strontium.

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(c) Magnesium is used in fireworks. It reacts rapidly with oxygen, burning with a bright white light. Magnesium reacts slowly with cold water.

Write an equation for the reaction of magnesium with oxygen.

Write an equation for the reaction of magnesium with cold water.

Give a medical use for the magnesium compound formed in the reaction of magnesium with cold water.

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(Total 10 marks)

Q7. Hydrazine (N2H4) decomposes in an exothermic reaction. Hydrazine also reacts exothermically with hydrogen peroxide when used as a rocket fuel.

(a) Write an equation for the decomposition of hydrazine into ammonia and nitrogen only.

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(b) State the meaning of the term mean bond enthalpy.

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(c) Some mean bond enthalpies are given in the table.

N–H N–N N≡N O–H O–O

Mean bond enthalpy / kJ mol−1 388 163 944 463 146

Use these data to calculate the enthalpy change for the gas-phase reaction between hydrazine and hydrogen peroxide.

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(Total 6 marks)

Q8. A student used Hess’s Law to determine a value for the enthalpy change that occurs when anhydrous copper(II) sulfate is hydrated. This enthalpy change was labelled ΔHexp by the student in a scheme of reactions.

(a) State Hess’s Law.

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(b) Write a mathematical expression to show how ΔHexp, ΔH1 and ΔH2 are related to each other by Hess’s Law.

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(c) Use the mathematical expression that you have written in part (b), and the data book values for the two enthalpy changes ΔH1 and ΔH2 shown, to calculate a value for ΔHexp

ΔH1 = −156 kJ mol−1

ΔH2 = +12 kJ mol−1

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(d) The student added 0.0210 mol of pure anhydrous copper(II) sulfate to 25.0 cm3 of deionised water in an open polystyrene cup. An exothermic reaction occurred and the temperature of the water increased by 14.0 °C.

(i) Use these data to calculate the enthalpy change, in kJ mol−1, for this reaction of copper(II) sulfate. This is the student value for ΔH1

In this experiment, you should assume that all of the heat released is used to raise the temperature of the 25.0 g of water. The specific heat capacity of water is 4.18 J K−1 g−1.

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(ii) Suggest one reason why the student value for ΔH1 calculated in part (d)(i) is less accurate than the data book value given in part (c).

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(e) Suggest one reason why the value for ΔHexp cannot be measured directly.

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(Total 8 marks)

Q9. The enthalpy of hydration for the chloride ion is −364 kJ mol−1 and that for the bromide ion is −335 kJ mol−1.

(a) By describing the nature of the attractive forces involved, explain why the value for the enthalpy of hydration for the chloride ion is more negative than that for the bromide ion.

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(b) The enthalpy of hydration for the potassium ion is −322 kJ mol−1. The lattice enthalpy of dissociation for potassium bromide is +670 kJ mol−1.

Calculate the enthalpy of solution for potassium bromide.

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(2)

(c) The enthalpy of solution for potassium chloride is +17.2 kJ mol−1.

(i) Explain why the free-energy change for the dissolving of potassium chloride in water is negative, even though the enthalpy change is positive.

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(ii) A solution is formed when 5.00 g of potassium chloride are dissolved in 20.0 g of water. The initial temperature of the water is 298 K.

Calculate the final temperature of the solution.

In your calculation, assume that only the 20.0 g of water changes in temperature and that the specific heat capacity of water is 4.18 J K−1 g−1.

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(Total 13 marks)

Q10. This question is about the extraction of metals.

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(a) Manganese can be extracted from Mn2O3 by reduction with carbon monoxide at high temperature.

(i) Use the standard enthalpy of formation data from the table and the equation for the extraction of manganese to calculate a value for the standard enthalpy change of this extraction.

Mn2O3(s) CO(g) Mn(s) CO2(g)

ΔHfϴ/ kJ mol−1 −971 −111 0 −394

Mn2O3(s) + 3CO(g) 2Mn(s) + 3CO2(g)

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(ii) State why the value for the standard enthalpy of formation of Mn(s) is zero.

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(b) Titanium is extracted in industry from titanium(IV) oxide in a two-stage process.

(i) Write an equation for the first stage of this extraction in which titanium(IV) oxide is converted into titanium(IV) chloride.

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(ii) Write an equation for the second stage of this extraction in which titanium(IV) chloride is converted into titanium.

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(c) Chromium is extracted in industry from chromite (FeCr2O4).

(i) In the first stage of this extraction, the FeCr2O4 is converted into Na2CrO4 Balance the equation for this reaction.

.........FeCr2O4 + .........Na2CO 3 + .........O 2 .........Na2CrO4 + 2Fe2O 3 + 8CO2

(1)

(ii) In the final stage, chromium is extracted from Cr2O3 by reduction with aluminium.

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Write an equation for this reaction.

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(Total 10 marks)

Q11. Antimony is a solid element that is used in industry. The method used for the extraction of antimony depends on the grade of the ore.

(a) Antimony can be extracted by reacting scrap iron with low-grade ores that contain antimony sulfide (Sb2S3).

(i) Write an equation for the reaction of iron with antimony sulfide to form antimony and iron(II) sulfide.

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(ii) Write a half-equation to show what happens to the iron atoms in this reaction.

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(b) In the first stage of the extraction of antimony from a high-grade ore, antimony sulfide is roasted in air to convert it into antimony(III) oxide (Sb2O3) and sulfur dioxide.


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(ii) Identify one substance that is manufactured directly from the sulfur dioxide formed in this reaction.

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(c) In the second stage of the extraction of antimony from a high-grade ore, antimony(III) oxide is reacted with carbon monoxide at high temperature.

(i) Use the standard enthalpies of formation in the table and the equation given below the table to calculate a value for the standard enthalpy change for this reaction.

Sb2O3(s) CO(g) Sb(I) CO2(g)

ΔHf / kJ mol–1 -705 -111 +20 -394

Sb2O3(s) + 3CO(g) 2Sb(I) + 3CO2(g)

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(ii) Suggest why the value for the standard enthalpy of formation of liquid antimony, given in the table above, is not zero.

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(iii) State the type of reaction that antimony(III) oxide has undergone in this reaction.

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(d) Deduce one reason why the method of extraction of antimony from a low-grade ore, described in part (a), is a low-cost process. Do not include the cost of the ore.

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(Total 10 marks)

Q12. Ethanol is an important industrial compound.

(a) Ethanol can be produced by the hydration of ethene. The equation for the equilibrium that is established is

H2C=CH2(g) + H2O(g) CH3CH2OH(g) ΔH = −42 kJ mol−1

The operating conditions for the process are a temperature of 300 oC and a pressure of 7 MPa. Under these conditions, the conversion of ethene into ethanol is 5%.

(i) Identify the catalyst used in this process. Deduce how an overall yield of 95% is achieved in this process without changing the operating conditions.

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(ii) Use your knowledge of equilibrium reactions to explain why a manufacturer might consider using an excess of steam in this process, under the same operating conditions.

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(iii) At pressures higher than 7 MPa, some of the ethene reacts to form a solid with a relative molecular mass greater than 5000.

Deduce the identity of this solid.

Give one other reason for not operating this process at pressures higher than 7 MPa. Do not include safety reasons.

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(b) Write an equation for the reaction that has an enthalpy change that is the standard enthalpy of formation of ethanol.

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(c) When ethanol is used as a fuel, it undergoes combustion.

(i) Define the term standard enthalpy of combustion.

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(ii) Consider these bond enthalpy data.

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C–H C–C C–O O=O C=O O–H

Bond enthalpy / kJ mol−1 412 348 360 496 805 463

Use these data and the equation to calculate a value for the enthalpy of combustion of gaseous ethanol.

CH3CH2OH(g) + 3O2(g) 2CO2(g) + 3H2O(g)

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(d) Gaseous ethanol can be used to convert hot copper(II) oxide into copper.

(i) Deduce the role of ethanol in this reaction.

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(ii) Draw the structure of the organic compound with Mr = 60 that is produced in this reaction.


Q13. The alcohol 2-methylpropan-2-ol, (CH3)3COH, reacts to form esters that are used as flavourings by the food industry. The alcohol can be oxidised to produce carbon dioxide and water.

A student carried out an experiment on a pure sample of 2-methylpropan-2-ol to determine its enthalpy of combustion. A sample of the alcohol was placed into a spirit burner and positioned under a beaker containing 50 cm3 of water. The spirit burner was ignited and allowed to burn for several minutes before it was extinguished.

The results for the experiment are shown in Table 1.

Table 1

Initial temperature of the water / °C 18.1

Final temperature of the water / °C 45.4

Initial mass of spirit burner and alcohol / g 208.80

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Final mass of spirit burner and alcohol / g 208.58

(a) Use the results from Table 1 to calculate a value for the heat energy released from the combustion of this sample of 2-methylpropan-2-ol. The specific heat capacity of water is 4.18 J K–1 g–1. Show your working.

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(b) Calculate the amount, in moles, of 2-methylpropan-2-ol burned in the experiment. Hence calculate a value, in kJ mol–1, for the enthalpy of combustion of 2-methylpropan-2-ol. Show your working.

(If you were unable to calculate an answer to part (a), you should assume that the heat energy released was 5580 J. This is not the correct value.)

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(c) An equation for the combustion of 2-methylpropan-2-ol is

(CH3)3COH(I) + 6O2(g) 4CO2(g) + 5H2O(I)

Table 2 contains some standard enthalpy of formation data.

Table 2

(CH3)3COH(I) O2(g) CO2(g) H2O(I)

∆Hf / kJ mol–1 –360 0 –393 –286

Use the data from Table 2 to calculate a value for the standard enthalpy of combustion of 2-methylpropan-2-ol. Show your working.

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(d) An accurate value for the enthalpy of combustion of 2-methylpropan-2-ol in which water is formed as a gas is –2422 kJ mol–1.

Use this value and your answer from part (b) to calculate the overall percentage error in the student’s experimental value for the enthalpy of combustion of 2-methylpropan-2-ol.

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(e) Suggest one improvement that would reduce errors due to heat loss in the student’s experiment.

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(f) Suggest one other source of error in the student’s experiment. Do not include heat loss, apparatus error or student error.

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(Total 11 marks)

Q14. Ethanol is an important fuel.

(a) A dilute aqueous solution of ethanol can be produced by the fermentation of an aqueous solution of glucose. It is claimed that the ethanol obtained from this solution is a carbon-neutral biofuel.

Write an equation for this fermentation reaction.

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Give two other essential conditions for this reaction to produce a good yield of ethanol.

Name a process used to produce a much more concentrated solution of ethanol from a dilute aqueous solution.

State the meaning of the term carbon-neutral in the context of this biofuel.

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(b) A student carried out a laboratory experiment to determine the enthalpy change when a sample of ethanol was burned. The heat produced was used to warm some water in a copper calorimeter. The student found that the temperature of 75.0 g of water increased by 5.50 °C when 2.40 × 10–3 mol of pure ethanol was burned in air.

Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of ethanol is burned. (The specific heat capacity of water is 4.18 J K–1 g–1)

Deduce two reasons why the student’s value for the standard enthalpy of combustion of ethanol is different from a Data Book value of –1279 kJ mol–1.

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(c) Mean bond enthalpies can be used to calculate enthalpies of reaction.

(i) Give the meaning of the term mean bond enthalpy.

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(ii) Consider the mean bond enthalpy data in the following table.

C—H C—C C—O O=O C=O O—H

Mean bond enthalpy / kJ mol–1 412 348 360 to be

calculated 805 463

Use the data in the table above and the equation shown to calculate a value for the bond enthalpy for the O=O double bond in an oxygen molecule.

CH3CH2OH(g) + 3O2(g) 2CO2(g) + 3H2O(g) ΔH = –1279 kJ mol–1

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(Total 15 marks)

Q15. Vanadium is an important metal. Ferrovanadium, an alloy of iron and vanadium, is used to make a strong type of vanadium-steel. Pure vanadium is used in nuclear reactors.

(a) The table shows some standard enthalpy of formation data.

V2O5(s) CaO(s)

ΔHfθ / kJ mol−1 −1560 −635

In the oldest method of extraction of vanadium, V2O5 is reacted with calcium at a high temperature.

5Ca(s) + V2O5(s) 2V(s) + 5CaO(s)

Use data from the table and the equation to calculate the standard enthalpy change for this reaction.

State the type of reaction that V2O5 has undergone.

Suggest one major reason why this method of extracting vanadium is expensive, other than the cost of heating the reaction mixture.

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(b) Ferrovanadium is produced by the reaction of aluminium with a mixture of V2O5 and iron(III) oxide.

Write an equation for the reaction of aluminium with iron(III) oxide.

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State the change in oxidation state of aluminium in this reaction.

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(c) Pure vanadium, for nuclear reactors, is formed by the reaction of hydrogen with purified VCl2

Write an equation for this reaction in which the only other product is HCl gas.

Identify two hazards in this process, other than the fact that it operates at a high temperature.

Deduce why this process produces pure vanadium, other than the fact that purified VCl2 is used.

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(Total 11 marks)

Q16. A value for the enthalpy of combustion of an alcohol can be determined using the apparatus shown in the diagram. The calorimeter is held in position by a clamp.

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This experiment can be repeated by using a different volume of water that would result in a more accurate value for the enthalpy of combustion because there would be a reduction in the heat lost.

State a change in the volume of water that would cause a reduction in heat loss and explain your answer.

Change in volume: _______________________________________________________

Explanation: ____________________________________________________________

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Q17. The table contains some bond enthalpy data.

Bond H−H O=O H−O

Bond enthalpy / kJ mol−1 436 496 464

(a) The value for the H−O bond enthalpy in the table is a mean bond enthalpy.

State the meaning of the term mean bond enthalpy for the H−O bond.

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(b) Use the bond enthalpies in the table to calculate a value for the enthalpy of formation of water in the gas phase.

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(c) The standard enthalpy of combustion of hydrogen, forming water in the gas phase, is almost the same as the correct answer to part (b).

(i) Suggest one reason why you would expect the standard enthalpy of combustion of hydrogen to be the same as the answer to part (b).

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(ii) Suggest one reason why you would expect the standard enthalpy of combustion of hydrogen to differ slightly from the answer to part (b).

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(Total 7 marks)

Q18. Alcohols such as methanol (CH3OH), ethanol (CH3CH2OH) and propan-1-ol (CH3CH2CH2OH) are good fuels.

(a) A student carried out an experiment to determine the enthalpy of combustion of methanol.

Methanol was placed in a spirit burner and the mass of the spirit burner measured. The student placed 100 g of water in a copper calorimeter and clamped it above the spirit burner. The burner was lit and allowed to burn for a few minutes. The flame was then extinguished and the new mass of the spirit burner found.

The measured temperature rise was 38.0 °C. The specific heat capacity of water is 4.18 J K−1 g−1.

A diagram of the apparatus is shown alongside a table which shows the

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measurements the student recorded.

Use the student’s data to calculate an experimental value for the enthalpy of combustion of methanol in kJ mol−1.

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(b) Suggest one reason, other than incomplete combustion or heat transfer to the atmosphere, why the student’s value for the enthalpy of combustion of methanol is different from that in a Data Book.

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(c) The uncertainty in each of the temperature readings from the thermometer in this experiment was ±0.25 °C. This gave an overall uncertainty in the temperature rise of ±0.5 °C.

Calculate the percentage uncertainty for the use of the thermometer in this experiment.

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(d) The student said correctly that using a thermometer with an overall uncertainty for the rise in temperature of ±0.5 °C was adequate for this experiment.

Explain why this thermometer was adequate for this experiment.

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(e) The enthalpy of combustion of ethanol is −1371 kJ mol−1. The density of ethanol is 0.789 g cm−3.

Calculate the heat energy released in kJ when 0.500 dm3 of ethanol is burned. Give your answer to an appropriate number of significant figures.

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(Total 10 marks)

Q19. (a) Propanone can be formed when glucose comes into contact with bacteria in the

absence of air.

(i) Balance the following equation for this reaction of glucose to form propanone, carbon dioxide and water.

.......C6H12O6 .......CH3COCH3 + .......CO2 + .......H2O (1)

(ii) Deduce the role of the bacteria in this reaction.

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(b) Propanone is also formed by the oxidation of propan−2−ol.

(i) Write an equation for this reaction using [O] to represent the oxidising agent.

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(ii) State the class of alcohols to which propan−2−ol belongs.

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(1)

(c) A student determined a value for the enthalpy change when a sample of propanone was burned. The heat produced was used to warm some water in a copper calorimeter. The student found that the temperature of 150 g of water increased by 8.0 °C when 4.50 × 10−3 mol of pure propanone was burned in air.

Use the student’s results to calculate a value, in kJ mol−1, for the enthalpy change when one mole of propanone is burned. (The specific heat capacity of water is 4.18 J K−1 g−1)

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(d) Define the term standard enthalpy of combustion.

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(e) Use the mean bond enthalpy data in the table and the equation given below the table to calculate a value for the standard enthalpy change when gaseous propanone is burned.

C−H C−C C−O O−H C=O O=O

Mean bond enthalpy / kJ mol−1

412 348 360 463 805 496

CH3COCH3(g) + 4O2(g) 3CO2(g) + 3H2O(g)

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(f) Suggest two reasons why the value obtained by the student in part (c) is different from the value calculated in part (e).

Reason 1 ___________________________________________________________

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Reason 2 ___________________________________________________________

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(Total 15 marks)

Q20. Standard enthalpy of combustion data can be used to calculate enthalpies of formation.

(a) State the meaning of the term standard enthalpy of combustion.

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(b) The equation corresponding to the enthalpy of formation of propan-1-ol is shown.

Table 1 contains some standard enthalpy of combustion data.

Table 1

C(s) H2(g) CH3CH2CH2OH(I)

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∆Hc⦵ / kJ mol–1 –394 –286 –2010

Use data from Table 1 to calculate a value for the standard enthalpy of formation of propan-1-ol. Show your working.

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(c) An equation for the complete combustion of gaseous propan-1-ol is shown.

Table 2 shows some bond enthalpy data.

Table 2

C–H C–O O–H C=O O=O

Bond enthalpy / kJ mol–1 412 360 463 805 496

Use data from Table 2 and the enthalpy change for this reaction to calculate a value for the bond enthalpy of a C–C bond in propan-1-ol.

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(Total 9 marks)

Q21. Hydrogen is produced by the reaction of methane with steam. The reaction mixture reaches a state of dynamic equilibrium.

CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ∆H = +206 kJ mol−1

Some enthalpy data is given in the table.

Bond C–H O–H H–H C≡H Bond enthalpy /

kJ mol−1 413 463 436 To be calculated

Use the information in the table and the stated enthalpy change to calculate the missing bond enthalpy.

A 234

B 1064

C 1476

D 1936 (Total 1 mark)

Q22. An engineer was trying to develop a new fuel for a motorboat by blending mixtures of different alcohols in order to find out which mixture released the most energy when used in the engine.

The engineer had a number of alcohols in unlabelled bottles. It was decided to identify the alcohols by determining their enthalpies of combustion and comparing these values with those from a data book.

(a) Outline a simple practical experiment that the engineer could use, including the measurements to be taken, in order to determine the enthalpy of combustion for one of the unknown alcohols. You do not need to include details of any calculations.

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(5)

(b) Other than heat loss to the surroundings, identify two major sources of error in the experiment. Do not refer to the precision of the equipment.

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(c) The engineer found that the experimental values for the enthalpies of combustion of butan-1-ol and methylpropan-2-ol were very similar and so these values could not be used to distinguish between the two alcohols.

Identify a reagent that the engineer could use to distinguish between these two alcohols. Give the observation in each case.

Reagent ___________________________________________________________

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Butan-1-ol __________________________________________________________

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Methylpropan-2-ol ____________________________________________________

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(d) The filter in the air intake for the engine in the motorboat may become partially blocked by dust and debris.

Explain with the aid of an equation why combustion of methylpropan-2-ol under these circumstances would be of economic and environmental concern to the engineer.

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(Total 13 marks)

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Q23. A 5.00 g sample of potassium chloride was added to 50.0 g of water initially at 20.0 °C. The mixture was stirred and as the potassium chloride dissolved, the temperature of the solution decreased.

(a) Describe the steps you would take to determine an accurate minimum temperature that is not influenced by heat from the surroundings.

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(b) The temperature of the water decreased to 14.6 °C.

Calculate a value, in kJ mol−1, for the enthalpy of solution of potassium chloride.

You should assume that only the 50.0 g of water changes in temperature and that the specific heat capacity of water is 4.18 J K−1 g−1. Give your answer to the appropriate number of significant figures.

Enthalpy of solution = _______________ kJ mol−1

(4)

(c) The enthalpy of solution of calcium chloride is −82.9 kJ mol−1. The enthalpies of hydration for calcium ions and chloride ions are −1650 and −364 kJ mol−1, respectively.

Use these values to calculate a value for the lattice enthalpy of dissociation of calcium chloride.

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Lattice enthalpy of dissociation = _______________ kJ mol−1

(2)

(d) Explain why your answer to part (c) is different from the lattice enthalpy of dissociation for magnesium chloride.

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(Total 12 marks)

Q24. (a) Write an equation, including state symbols, for the reaction with enthalpy change

equal to the standard enthalpy of formation for CF4(g).

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(b) Explain why CF4 has a bond angle of 109.5°.

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(c) Table 1 gives some values of standard enthalpies of formation (ΔfHϴ).

Table 1

Substance F2(g) CF4(g) HF(g)

ΔfHϴ / kJ mol−1 0 −680 −269

The enthalpy change for the following reaction is −2889 kJ mol−1.

C2H6(g) + 7F2(g) 2CF4(g) + 6HF(g)

Use this value and the standard enthalpies of formation in Table 1 to calculate the standard enthalpy of formation of C2H6(g).

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Standard enthalpy of formation of C2H6(g) = ____________________ kJ mol−1

(3)

(d) Methane reacts violently with fluorine according to the following equation.

CH4(g) + 4F2(g) CF4(g) + 4HF(g) ΔH = −1904 kJ mol−1

Some mean bond enthalpies are given in Table 2.

Table 2

Bond C−H C−F H−F

Mean bond enthalpy / kJ mol−1 412 484 562

A student suggested that one reason for the high reactivity of fluorine is a weak F−F bond.


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(Total 10 marks)

Q25. Many chemical processes release waste products into the atmosphere. Scientists are developing new solid catalysts to convert more efficiently these emissions into useful products, such as fuels. One example is a catalyst to convert these emissions into methanol. The catalyst is thought to work by breaking a H–H bond.

An equation for this formation of methanol is given below.


Some mean bond enthalpies are shown in the following table.

Bond C=O C–H C–O O–H

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Mean bond enthalpy / kJ mol−1 743 412 360 463

(a) Use the enthalpy change for the reaction and data from the table to calculate a value for the H–H bond enthalpy.

H–H bond enthalpy = _______________ kJ mol−1

(3)

(b) A data book value for the H–H bond enthalpy is 436 kJ mol−1.

Suggest one reason why this value is different from your answer to part (a).

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(c) Suggest one environmental advantage of manufacturing methanol fuel by this reaction.

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(d) Use Le Chatelier's principle to justify why the reaction is carried out at a high pressure rather than at atmospheric pressure.

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(e) Suggest why the catalyst used in this process may become less efficient if the carbon dioxide and hydrogen contain impurities.

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(f) In a laboratory experiment to investigate the reaction shown in the equation below, 1.0 mol of carbon dioxide and 3.0 mol of hydrogen were sealed into a container. After the mixture had reached equilibrium, at a pressure of 500 kPa, the yield of methanol was 0.86 mol.

CO2(g) + 3H2(g) CH3OH(g) + H2O(g)

Calculate a value for Kp

Give your answer to the appropriate number of significant figures. Give units with your answer.

Kp = _______________ Units = _______________ (7)

(Total 16 marks)

Q26. The figure below shows apparatus used in an experiment to determine the enthalpy of combustion of leaf alcohol.

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The alcohol is placed in a spirit burner and weighed. The burner is lit and the alcohol allowed to burn for a few minutes. The flame is extinguished and the burner is re-weighed. The temperature of the water is recorded before and after heating.

The following table shows the results obtained.

Initial mass of spirit burner and alcohol / g 56.38

Final mass of spirit burner and alcohol / g 55.84

Initial temperature of water / °C 20.7

Final temperature of water / °C 40.8

(a) Write an equation for the complete combustion of leaf alcohol (CH3CH2CH=CHCH2CH2OH).

___________________________________________________________________ (1)

(b) Use the results from the table above to calculate a value for the enthalpy of combustion of leaf alcohol. Give units in your answer. (The specific heat capacity of water is 4.18 J K−1 g−1)

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Enthalpy of combustion = ____________ Units = ____________ (4)

(c) State how your answer to part (b) is likely to differ from the value quoted in reference sources. Give one reason for your answer.

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(d) A 50.0 g sample of water was used in this experiment.

Explain how you could measure out this mass of water without using a balance.

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(Total 9 marks)

Q27. Calculate the enthalpy change, in kJ, for this dissociation of mole of propan-1-ol.

C3H7OH(g) ⟶ 3C(g) + 8H(g) + O(g)

Mean bond dissociation enthalpy / kJ mol−1 412 348 360 463

A −4751

B −4403

C +4403


Q28.

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What is the temperature rise, in K, when 504 J of heat energy are absorbed by 0.110 kg of solid iron? Specific heat capacity of iron = 0.448 J K−1 g−1

A 9.78 × 10−2

B 1.02 × 101

C 2.83 × 102

D 1.02 × 104

(Total 1 mark)

Q29. Hydrogen can be manufactured by the reaction of methane with steam. An equilibrium is established as shown by the equation.

CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)

(a) Use Le Chatelier’s principle to predict the effect on the equilibrium yield of hydrogen if the overall pressure is increased. Explain your answer.

Effect on yield _______________________________________________________

Explanation _________________________________________________________

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(b) Explain why the equilibrium yield of hydrogen is unchanged if a catalyst is used in the reaction.

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(c) The table shows the standard enthalpy of formation and the standard entropy for each substance in this equilibrium reaction.

CH4(g) H2O(g) CO(g) H2(g)

ΔfHθ / kJ mol−1 −75 −242 −111 0

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Sθ / J K−1 mol−1 186 189 198 131

Use data from the table to calculate the standard enthalpy change for this equilibrium reaction.

Standard enthalpy change _____________ kJ mol−1

(2)

Use your answer from part (c) and the entropy data from the table above to calculate the minimum temperature, in °C, needed for this reaction to be feasible. Give your answer to the appropriate number of significant figures.

(If you did not complete part (c) you should assume a value of 120 kJ mol−1 for the standard enthalpy change. This is not the correct value).

Minimum temperature _________ °C (5)

(Total 12 marks)

Q30. A student carried out a reaction between magnesium ribbon and aqueous trichloroethanoic acid in order to determine the enthalpy change. The equation for the reaction is shown:

Mg(s) + 2H+(aq) ⟶ Mg2+(aq) + H2(g)

The student measured the initial temperature of the trichloroethanoic acid and again every minute for 3 minutes before adding the magnesium ribbon at the fourth minute. The student continued to measure the temperature every minute for a further 10 minutes. The graph for these measurements is shown below.

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The student used 240 mg of magnesium and 10.0 cm3 of aqueous trichloroethanoic acid (an excess).

Use these data and information determined from the graph above to calculate the enthalpy change, in kJ mol−1, for this reaction. Show your working. Give your answer to an appropriate precision. (The specific heat capacity of water = 4.18 J K−1 g−1)

Enthalpy change = ___________ kJ mol−1

(Total 7 marks)

Q31. This question is about energetics.

(a) Write an equation, including state symbols, for the reaction with an enthalpy change equal to the enthalpy of formation for iron(III) oxide.

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(b) Table 1 contains some standard enthalpy of formation data.

Table 1

CO(g) Fe2O3(s)

ΔfHo/ kJ mol−1 −111 −822

Fe2O3(s) + 3CO(g) ⟶ 2Fe(s) + 3CO2(g) ΔH = −19 kJ mol−1

Use these data and the equation for the reaction of iron(III) oxide with carbon monoxide to calculate a value for the standard enthalpy of formation for carbon dioxide.

Show your working.

ΔfHo ____________________ kJ mol−1

(3)

(c) Some enthalpy data are given in Table 2.

Table 2

Process ΔH / kJ mol−1

N2(g) + 3H2(g) ⟶ 2NH3(g) −92

N2(g) ⟶ 2N(g) +944

H2(g) ⟶ 2H(g) +436

Use the data from Table 2 to calculate the bond enthalpy for N−H in ammonia.

N−H bond enthalpy ____________________ kJ mol−1

(3)

(d) Give one reason why the bond enthalpy that you calculated in part (c) is different from the mean bond enthalpy quoted in a data book (388 kJ mol−1).

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(Total 8 marks)

Q32. Anhydrous magnesium chloride, MgCl2, can absorb water to form the hydrated salt MgCl2.4H2O

MgCl2(s) + 4H2O(l) ⟶ MgCl2.4H2O(s)

(a) Suggest one reason why the enthalpy change for this reaction cannot be determined directly by calorimetry.

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(b) Some enthalpies of solution are shown in Table 1.

Table 1

Salt Enthalpy of solution / kJ mol−1

MgCl2(s) −155

MgCl2.4H2O(s) −39

Calculate the enthalpy change for the absorption of water by MgCl2(s) to form MgCl2.4H2O(s).

Enthalpy change _________________________________________ kJ mol−1

(2)

(c) Describe how you would carry out an experiment to determine the enthalpy of solution of anhydrous magnesium chloride.

You should use about 0.8 g of anhydrous magnesium chloride.

Explain how your results could be used to calculate the enthalpy of solution.

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(d) Anhydrous magnesium chloride can be formed by direct reaction between its elements.

Mg(s) + Cl2(g) ⟶ MgCl2(s)

The free-energy change, ΔG, for this reaction varies with temperature as shown in Table 2.

Table 2

T / K ΔG / kJ mol−1

298 −592.5

288 −594.2

273 −596.7

260 −598.8

240 −602.2

Use these data to plot a graph of free-energy change against temperature on the grid below.

Calculate the gradient of the line on your graph and hence calculate the entropy change, ΔS, in J K−1 mol−1, for the formation of anhydrous magnesium chloride from its elements.

Show your working.

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ΔS _________________________________________ J K−1 mol−1

(5)

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(Total 14 marks)

Q33. This question is about enthalpy changes.

(a) Write an equation, including state symbols, to show the reaction taking place when the standard enthalpy of combustion for ethanol is measured.

___________________________________________________________________ (2)

(b) State the name given to the enthalpy change represented by the following chemical equation.

Explain why this enthalpy change would be difficult to determine directly.

Enthalpy change ____________________________________________________

Explanation ________________________________________________________

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(c) Standard enthalpies of combustion for carbon and carbon monoxide are −393 kJ mol−1 and −283 kJ mol−1, respectively.

Use these data to calculate the enthalpy change for the reaction in part (b).

Enthalpy change = ________ kJ mol−1

(2)

(d) Use the following data to calculate a value for the Xe–F bond enthalpy in XeF4

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Xe–F bond enthalpy = _____ kJ mol−1

(3)

(e) Suggest a reason why the value calculated in part (d) differs from the mean Xe–F bond enthalpy quoted in a data source.

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(Total 10 marks)

Q34. A student planned and carried out an experiment to determine the enthalpy of reaction when magnesium metal displaces zinc from aqueous zinc sulfate.

Mg(s) + Zn2+(aq) ⟶ Mg2+(aq) + Zn(s)

The student used this method:

• A measuring cylinder was used to transfer 50 cm3 of a 1.00 mol dm−3 aqueous solution of zinc sulfate into a glass beaker.

• A thermometer was placed in the beaker.

• 2.08 g of magnesium metal powder were added to the beaker.

• The mixture was stirred and the maximum temperature recorded.

The student recorded a starting temperature of 23.9 °C and a maximum temperature of 61.2 °C.

(a) Show by calculation which reactant was in excess.

Use the data to calculate the experimental value for enthalpy of reaction in kJ mol−1(Assume that the specific heat capacity of the solution is 4.18 J K−1g−1and the density of the solution is 1.00 g cm−3).

Reactant in excess ____________________

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Enthalpy of reaction ____________________ kJ mol−1

(6)

(b) Another student used the same method and obtained a value for the enthalpy of reaction of −142 kJ mol−1

A data book value for the enthalpy of reaction is −310 kJ mol−1

Suggest the most likely reason for the large difference between the student’s experimental value and the data book value.

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(c) Suggest how the students’ method, and the analysis of the results, could be improved in order to determine a more accurate value for the enthalpy of reaction.

Justify your suggestions.

Do not refer to the precision of the measuring equipment. Do not change the amounts or the concentration of the chemicals.

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(Total 13 marks)

Q35. When alkanes are burned in an excess of oxygen they produce carbon dioxide and water.

(a) Write an equation for the complete combustion of propane in oxygen.

___________________________________________________________________ (1)

(b) An expression can be derived using bond enthalpy data to estimate the enthalpy of combustion (ΔcH) of an alkane.

For an alkane with n carbon atoms: ΔcH = − (496n + 202) kJ mol−1

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The enthalpy of combustion of an alkane was calculated to be −6650 kJ mol−1 using this expression.


Show your working.

Molecular formula of alkane _________________________________________ (2)

(c) Suggest one reason, other than the use of mean bond enthalpies, why a value for the enthalpy of combustion of a liquid alkane is different from the value obtained using the expression in part (b)

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___________________________________________________________________ (1)

(d) Values of the enthalpy change for combustion of 1 g of some alkanes are shown in the table.

methane ethane propane butane pentane

Enthalpy change in kJ for combustion of 1 g

−55.6 −52.0 −49.6 −48.7

Plot the enthalpy change for the combustion of 1 g against the number of carbon atoms in the alkanes in the table.

Draw a best fit line and use this to estimate the enthalpy change for combustion of 1 g of propane.

Write your answer in the table.

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(3)

(e) Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in cars.

When isooctane is burned, the enthalpy change is −47.8 kJ g−1

Isooctane is a liquid at room temperature with a density of 0.692 g cm−3

Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in excess oxygen.


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Heat energy released ____________________ kJ (2)

(Total 9 marks)

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Mark schemes

Q1. (a) q = 500 × 4.18 × 40

Do not penalise precision. 1

= 83600 J Accept this answer only. Ignore conversion to 83.6 kJ if 83600 J shown. Unit not required but penalise if wrong unit given. Ignore the sign of the heat change. An answer of 83.6 with no working scores one mark only. An answer of 83600 with no working scores both marks.

1

(b) Moles (= 83.6 / 51.2) = 1.63 Using 77400 alternative gives 1.51 mol Allow (a) in kJ / 51.2 Do not penalise precision.

1

Mass = 1.63 × 40(.0) = 65.2 (g) Allow 65.3 (g) Using 77400 alternative gives 60.4 to 60.5 Allow consequential answer on M1. 1 mark for Mr (shown, not implied) and 1 for calculation. Do not penalise precision.

2

(c) Molarity = 1.63 / 0.500 = 3.26 mol dm–3 Allow (b) M1 × 2 Using 1.51 gives 3.02

1

(d) Container splitting and releasing irritant / corrosive chemicals Must have reference to both aspects; splitting or leaking (can be implied such as contact with body / hands) and hazardous chemicals. Allow ‘burns skin / hands’ as covering both points Ignore any reference to ‘harmful’. Do not allow ‘toxic’.

1

(e) (i) 4Fe + 3O2 → 2Fe2O3

Allow fractions / multiples in equation. Ignore state symbols.

1

(ii) Iron powder particle size could be increased / surface area lessened Decrease in particle size, chemical error = 0 / 3 Change in oxygen, chemical error = 0 / 3

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1

Not all the iron reacts / less reaction / not all energy released / slower release of energy / lower rate of reaction

Mark points M2 and M3 independently. 1

Correct consequence of M2 An appropriate consequence, for example • too slow to warm the pouch effectively • lower temperature reached • waste of materials

1

(f) (i) Conserves resources / fewer disposal problems / less use of landfill / fewer waste products

Must give a specific point. Do not allow ‘does not need to be thrown away’ without qualification. Do not accept ‘no waste’.

1

(ii) Heat to / or above 80 °C (to allow thiosulfate to redissolve) Accept ‘heat in boiling water’. If steps are transposed, max 1 mark.

1

Allow to cool before using again Reference to crystallisation here loses this mark.

1 [14]

Q2. B

[1]

Q3. (a) Temperature on y-axis

If axes unlabelled use data to decide that temperature is on y-axis.

1

Uses sensible scales Lose this mark if the plotted points do not cover half of the paper. Lose this mark if the temperature axis starts at 0 °C.

1

Plots all of the points correctly ± one square Lose this mark if the graph plot goes off the squared paper.

1

Draws two best-fit lines

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Candidate must draw two correct lines. Lose this mark if the candidate’s line is doubled or kinked.

1

Both extrapolations are correct to the 4th minute Award this mark if the candidate’s extrapolations are within one square of your extrapolations of the candidate’s best-fit lines at the 4th minute.

1

(b) 19.5 (°C) Accept this answer only.

1

(c) 26.5 ± 0.2 (°C) Do not penalise precision.

1

(d) (c) – (b) Only award this mark if temperature rise is recorded to 1 d.p.

1

(e) Uses mcΔT equation Allow use of this equation with symbols or values for M1 even if the mass is wrong.

1

Correct value using 25 × 4.18 × (d) 7.0 gives 732 J. Correct answer with no working scores one mark only. Do not penalise precision. Allow answer in J or kJ. Ignore sign of enthalpy change.

1

(f) 9.0(1) × 10–3

Do not allow 0.01 Allow 9 × 10–3 or 0.009 in this case.

1

(g) If answer to (e) in J, then (e) / (1000 × (f))

or

If answer to (e) in kJ, then (e) / (f) 7.0 and 9.01 × 10–3 gives 81.2 kJ mol–1

If answer to (e) is in J must convert to kJ mol–1 correctly to score mark.

1

Enthalpy change has negative sign Award this mark independently, whatever the calculated value of the enthalpy change.

1

(h) The idea that this ensures that all of the solution is at the same temperature

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Do not allow ‘to get an accurate reading’ without qualification. 1

(i) (i) Chlorine is toxic / poisonous / corrosive Do not allow ‘harmful’.

1

(ii) Explosion risk / apparatus will fly apart / stopper will come out Ignore ‘gas can’t escape’ or ‘gas can’t enter the tube’.

1 [16]

Q4. (a) (i) M1 (could be scored by a correct mathematical expression which must

have all ∆Hsymbols and the ∑ or SUM)

M1 ΔHr = ΣΔHf (products) - ΣΔHf (reactants)

OR a correct cycle of balanced equations with 1C, 3H2 and 1O2

M2 ΔHr = – 201 + (– 242) – (– 394) ΔHr = – 201 – 242 + 394 ΔHr = – 443 + 394 (This also scores M1)

M3 = – 49 (kJ mol–1) (Award 1 mark ONLY for + 49) Correct answer gains full marks Credit 1 mark ONLY for + 49 (kJ mol–1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either correct cycle of balanced equations with 1C, 3H2 and 1O2

OR a clear statement of M1 which could be in words and scores only M1

3

(ii) It is an element / elemental Ignore reference to “standard state”

OR

By definition 1

(b) M1 (The yield) increases / goes up / gets more If M1 is given as “decreases” / “no effect” / “no change” then CE= 0 for clip, but mark on only M2 and M3 from a blank M1

M2 There are more moles / molecules (of gas) on the left / of reactants OR fewer moles / molecules (of gas) on the right / products

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OR there are 4 moles /molecules (of gas) on the left and 2 moles / molecules on the right. OR (equilibrium) shifts / moves to the side with less moles / molecules

Ignore “volumes”, “particles” “atoms” and “species” for M2

M3: Can only score M3 if M2 is correct

The (position of) equilibrium shifts / moves (from left to right) to oppose the increase in pressure

For M3, not simply “to oppose the change” For M3 credit the equilibrium shifts / moves (to right) to lower / decrease the pressure (There must be a specific reference to the change that is opposed)

3

(c) M1 Yield increases goes up

M2 The (forward) reaction / to the right is endothermic OR takes in/ absorbs heat

OR

The reverse reaction / to the left is exothermic OR gives out / releases heat If M1 is given as “decrease” / “no effect” / “no change” then CE= 0 for clip, but mark on only M2 and M3 from a blank M1

Can only score M3 if M2 is correct

M3 The (position of) equilibrium shifts / moves (from left to right) to oppose the increase in temperature (QoL)

For M3, not simply “to oppose the change” For M3, credit the (position of) equilibrium shifts / moves (QoL) to absorb the heat OR to cool the reaction OR to lower the temperature (There must be a specific reference to the change that is opposed)

3

(d) (i) An activity which has no net / overall (annual) carbon emissions to the atmosphere OR An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere. OR There is no change in the total amount / level of carbon dioxide /CO2 carbon /greenhouse gas present in the atmosphere.

The idea that the carbon /CO2 given out equals the carbon /CO2 that was taken in from the atmosphere

1

(ii) CH3OH + 1½ O2 CO2 + 2H2O Ignore state symbols

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Accept multiples 1

(iii) 3H2 + 1½ O2 3H2O Ignore state symbols

OR Accept multiples

2H2 + O2 2H2O Extra species must be crossed through

1

(e) M1 q = m c ∆T Award full marks for correct answer Ignore the case for each letter

OR q = 140 × 4.18 × 7.5

M2 = 4389 (J) OR 4.389 (kJ) OR 4.39 (kJ) OR 4.4 (kJ)(also scores M1)

M3 Using 0.0110 mol therefore ∆H = – 399 (kJmol–1 ) OR – 400

Penalise M3 ONLY if correct numerical answer but sign is incorrect; +399 gains 2 marks Penalise M2 for arithmetic error and mark on In M1, do not penalise incorrect cases in the formula If ∆T = 280.5; score q = m c ∆T only If c = 4.81 (leads to 5050.5) penalise M2 ONLY and mark on for M3 = – 459

+399 or +400 gains 2 marks Ignore incorrect units

3 [16]

Q5. (a) (Enthalpy change to) break the bond in 1 mol of chlorine (molecules)

Allow (enthalpy change to) convert 1 mol of chlorine molecules into atoms Do not allow energy or heat instead of enthalpy, allow heat energy

1

To form (2 mol of) gaseous chlorine atoms / free radicals Can score 2 marks for ‘Enthalpy change for the reaction’: Cl2(g) → 2Cl(g) Equation alone gains M2 only Can only score M2 if 1 mol of chorine molecules used in M1 (otherwise it would be confused with atomisation enthalpy) Any mention of ions, CE = 0

1

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(b) (For atomisation) only 1 mol of chlorine atoms, not 2 mol (as in bond enthalpy) is formed / equation showing ½ mol chlorine giving 1 mol of atoms

Allow breaking of one bond gives two atoms Allow the idea that atomisation involves formation of 1 mol of atoms not 2 mol Allow the idea that atomisation of chlorine involves half the amount of molecules of chlorine as does dissociation Any mention of ions, CE = 0

1

(c) (i) ½F2(g) + ½Cl2(g) → ClF(g) 1

(ii) ΔH = ½E(F–F) + ½ E(Cl−Cl) – E(Cl−F) Allow correct cycle

1

E(Cl−F) = ½E(F–F) + ½E(Cl−Cl) − ΔH

= 79 + 121 − (−56)

= 256 (kJ mol−1) −256 scores zero Ignore units even if wrong

1

(iii) ½Cl2 + 3/2 F2 → ClF3

If equation is doubled CE=0 unless correcr answer gained by / 2 at end This would score M1

1

ΔH = ½ E(Cl−Cl) + 3/2 E(F–F) − 3E(Cl−F)

= 121 + 237 − 768 / (or 3 × value from (c)(ii)) This also scores M1 (note = 358 − 768)

1

= −410 (kJ mol−1) If given value of 223 used ans = −311 Allow 1 / 3 for +410 and +311

1

(iv) (Bond enthalpy of) Cl−F bond in ClF is different from that in ClF3

Allow Cl-F bond (enthalpy) is different in different compounds (QoL)

1

(d) NaCl is ionic / not covalent 1

[11]

Q6. (a) M1 (could be scored by a correct mathematical expression

Correct answer to the calculation gains all of M1, M2 and M3

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M1 ΔH = ΣΔHf (products) − ΣΔH f (reactants) Credit 1 mark for − 101 (kJ mol−1)


M2 = − 1669 − 3(− 590) = − 1669 + 1770 (This also scores M1)

M3 = + 101 (kJ mol−1)

Award 1 mark ONLY for − 101 For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 3Sr and 2Al OR a clear statement of M1 which could be in words and scores only M1

M4 - Using powders Any one from

• To increase collision frequency / collisions in a given time / rate of collisions

• To increase the surface contact / contact between the solids / contact between (exposed) particles

Ignore dividing final answer by 3 Penalise M4 for reference to molecules.

5

M5 Major reason for expense of extraction Any one from

• Aluminium is extracted by electrolysis OR aluminium extraction uses (large amounts of) electricity

• Reaction / process / It / the mixture requires heat

• It is endothermic

(b) Calcium has a higher melting point than strontium, because Ignore general Group 2 statements.

Correct reference to size of cations / proximity of electrons M1 (For Ca) delocalised electrons closer to cations / positive ions / atoms / nucleus OR cations / positive ions / atoms are smaller OR cation / positive ion / atom or it has fewer (electron) shells / levels

Penalise M1 if either of Ca or Sr is said to have more or less delocalised electrons OR the same nuclear charge. Ignore reference to shielding.

Relative strength of metallic bonding M2 (Ca) has stronger attraction between the cations / positive ions / atoms / nucleus and the delocalised electrons

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OR stronger metallic bonding

(assume argument refers to Ca but credit converse argument for Sr) CE= 0 for reference to molecules or Van der Waals forces or intermolecular forces or covalent bonds.

2

(c) M1 2Mg + O2 2MgO

M2 Mg + 2H2O Mg(OH)2 + H2

Credit multiples of the equations.

M3 Magnesium hydroxide is used as an antacid / relieve indigestion (heartburn) / neutralise (stomach) acidity / laxative

Not simply “milk of magnesia” in M3 3

[10]

Q7. (a) 3N2H4 4NH3 + N2

Or multiples Ignore state symbols

1

(b) M1 enthalpy / heat (energy) change / required / needed to break / dissociate a covalent bond (or a specified covalent bond)

Ignore bond making Ignore standard conditions M2 requires an attempt at M1

M2 average / mean over different molecules / compounds / substances 2

(c) M1 ⅀ (bonds broken) − ⅀ (bonds formed) = ΔH

M1 could stand alone

OR

Sum of bonds broken − Sum of bonds formed = ΔH Award full marks for correct answer

M2 (also scores M1) Ignore units

4(+388) + 163 + 2(146) + 4(463) − 944 − 8(463) = ΔH OR broken +3859 (2007) formed − 4648 (2796)

M3

ΔH = − 789 (kJ mol−1) Two marks can score with an arithmetic error in the working

Award 1 mark for + 789

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Credit one mark only for calculating either the sum of the bonds broken or the sum of the bonds formed provided this is the only mark that is to be awarded


[6]

Q8. (a) The enthalpy change / heat (energy) change (at constant pressure) in a reaction is

independent of the route / path taken (and depends only on the initial and final states) Ignore the use of ΔH for enthalpy

1

(b) ΔHexp + ΔH2 – ΔH1 = 0 Any correct mathematical statement that uses all three terms

OR

ΔHexp + ΔH2 = ΔH1 OR ΔH1 = ΔHexp + ΔH2

OR

ΔHexp= ΔH1 – ΔH2 OR ΔHexp = ΔH1 +( – ΔH2 ) 1

(c) ΔHexp = ΔH1 – ΔH2

ΔHexp = −156 −12 = −168 (kJ mol−1) Ignore units

Award the mark for the correct answer without any working 1

(d) (i) M1 q = m c ΔT OR calculation (25.0 x 4.18 x 14.0) Award full marks for correct answer

M2 = 1463J OR 1.46 kJ (This also scores M1) In M1, do not penalise incorrect cases in the formula

M3 must have both the correct value within the range specified and the minus sign

Penalise M3 ONLY if correct numerical value but sign is incorrect; e.g. +69.5 to +69.7 gains 2 marks (ignore +70 after correct answer)

For 0.0210 mol, therefore

ΔH1 = − 69.67 to − 69.52 (kJ mol-1)

OR ΔH1 = − 69.7 to − 69.5 (kJ mol−1) Penalise M2 for arithmetic error but mark on

Accept answers to 3sf or 4sf in the range − 69.7 to − 69.5 ΔT = 287, score q = m c ΔT only

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Ignore -70 after correct answer If c = 4.81 (leads to 1684J ) penalise M2 ONLY and mark on for M3 = − 80.17 (range − 80.0 to − 80.2) Ignore incorrect units

3

(ii) The idea of heat loss NOT impurity

OR

Incomplete reaction (of the copper sulfate) NOT incompetence

OR

Not all the copper sulfate has dissolved NOT incomplete combustion

1

(e) Impossible to add / react the exact / precise amount of water Not just “the reaction is incomplete”

OR

Very difficult to measure the temperature rise of a solid

OR

Difficult to prevent solid dissolving

OR

(Copper sulfate) solution will form 1

[8]

Q9. (a) Chloride (ions) are smaller (than bromide ions)

Must state or imply ions. Allow chloride has greater charge density (than bromide). Penalise chlorine ions once only (max 2 / 3).

1

So the force of attraction between chloride ions and water is stronger This can be implied from M1 and M3 but do not allow intermolecular forces.

1

Chloride ions attract the δ+ on H of water / electron deficient H on water Allow attraction between ions and polar / dipole water. Penalise H+ (ions) and mention of hydrogen bonding for M3 Ignore any reference to electronegativity. Note: If water not mentioned can score M1 only.

1

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(b) ΔHsolution = ΔHL + ΔHhyd K+ ions + ΔHhyd Br − ions / = 670 − 322 − 335

Allow ΔHsolution= ΔHL + ΣΔHhyd

1

= (+)13 (kJ mol−1) Ignore units even if incorrect. +13 scores M1 and M2 −13 scores 0 −16 scores M2 only (transcription error).

1

(c) (i) The entropy change is positive / entropy increases ΔS is negative loses M1 and M3

1

Because 1 mol (solid) → 2 mol (aqueous ions) / no of particles increases Allow the aqueous ions are more disordered (than the solid). Mention of atoms / molecules loses M2

1

Therefore TΔS > ΔH 1

(ii) Amount of KCl = 5/Mr = 5/74.6 = 0.067(0) mol If moles of KCl not worked out can score M3, M4 only (answer to M4 likely to be 205.7 K)

1

Heat absorbed = 17.2 × 0.0670 = 1.153 kJ Process mark for M1 × 17.2

1

Heat absorbed = mass × sp ht × ΔT

(1.153 × 1000) = 20 × 4.18 × ΔT If calculation uses 25 g not 20, lose M3 only (M4 = 11.04, M5 = 287)

1

ΔT = 1.153 × 1000 / (20 × 4.18) = 13.8 K If 1000 not used, can only score M1, M2, M3 M4 is for a correct ΔT Note that 311.8 K scores 4 (M1, M2, M3, M4).

1

T = 298 − 13.8 = 284(.2) K If final temperature is negative, M5 = 0 Allow no units for final temp, penalise wrong units.

1 [13]


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have all ΔH symbols and the ⅀ or SUM) Correct answer gains full marks Credit 1 mark ONLY if –122 (kJ mol−1)

M1 ΔH = ⅀ΔHf (products) - ⅀ΔHf (reactants)


M2 ΔH = 3(−394) − 3(−111) − (−971) (This also scores M1)

M3 = (+) 122(kJ mol−1)

Award 1 mark ONLY for –122

For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for correct method; this requires either a correct cycle of balanced equations OR a clear statement of M1 which could be in words and scores M1 only

3

(ii) By definition Ignore reference to “standard state”

OR

Because it is an element / elemental 1

(b) (i) TiO2 + 2Cl 2 + 2C TiCl4 + 2CO Allow multiples

OR

TiO2 + 2Cl 2 + C TiCl4CO2

Ignore state symbols

M1 use of Cl2 and C

M2 a correct balanced equation 2

(ii) TiCl4 + 4Na Ti + 4NaCl Allow multiples

OR

TiCl4 + 2Mg Ti + 2MgCl2

Ignore state symbols

M1 use of Na OR Mg

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M2 a correct balanced equation 2

(c) (i) 4 FeCr2O4 + 8 Na2CO3 + 7O2 8Na2CrO4 + 2Fe2O3 + 8CO2

Allow multiples Ignore state symbols

1

(ii) Cr2O3 + 2Al Al2O3 + 2Cr Allow multiples Ignore state symbols

1 [10]

Q11. (a) (i) 3Fe + Sb2S3 3FeS + 2Sb


1

(ii) Fe Fe2+ + 2e−

Ignore charge on the electron unless incorrect. Or multiples. Credit the electrons being subtracted on the LHS. Ignore state symbols.

1

(b) (i) Sb2S3 + 4.5O2 Sb2O3 + 3SO2


1

(ii) SO3 or sulfur trioxide / sulfur (VI) oxide Credit also the following ONLY. H2SO4 or sulfuric acid. OR Gypsum / CaSO4 or plaster of Paris.

1

(c) (i) M1 (could be scored by a correct mathematical expression) Correct answer gains full marks.

M1 ∆Hr = Ʃ∆Hf(products) − Ʃ∆Hf(reactants)

OR a correct cycle of balanced equations / correct numbers of moles Credit 1 mark for +104 (kJ mol−1).

M2 = 2(+20) + 3(−394) − (−705) − 3(−111)

= 40 −1182 + 705 + 333

= −1142 − (−1038)

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M3 = −104 (kJ mol−1)

(Award 1 mark ONLY for + 104) For other incorrect or incomplete answers, proceed as follows: • Check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks. • If no AE, check for a correct method; this requires either a correct cycle with 3CO, 2Sb and 3CO2 OR a clear statement of M1 which could be in words and scores only M1.

3

(ii) It / Sb is not in its standard state

OR

Standard state (for Sb) is solid / (s)

OR

(Sb) liquid is not its standard state Credit a correct definition of standard state as an alternative to the words ‘standard state’. QoL

1

(iii) Reduction OR reduced OR redox 1

(d) Low-grade ore extraction / it

• uses (cheap) scrap / waste iron / steel

• is a single-step process

uses / requires less / low(er) energy Ignore references to temperature / heat or labour or technology.

1 [10]

Q12. (a) (i) M1 c(oncentrated) phosphoric acid / c(onc.) H3PO4

OR c(oncentrated) sulfuric acid / c(onc.) H2SO4

In M1, the acid must be concentrated. Ignore an incorrect attempt at the correct formula that is written in addition to the correct name.

M2 Re-circulate / re-cycle the (unreacted) ethene (and steam) / the reactants OR pass the gases over the catalyst several / many times

In M2, ignore “remove the ethanol”.

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Credit “re-use”. 2

(ii) M1 (By Le Chatelier’s principle) the equilibrium is driven / shifts / moves to the right / L to R / forwards / in the forward direction

M2 depends on a correct statement of M1 The equilibrium moves / shifts to

• oppose the addition of / increased concentration of / increased moles / increased amount of water / steam

• to decrease the amount of steam / water

Mark M3 independently M3 Yield of product / conversion increase OR ethanol increases / goes up / gets more

3

(iii) M1 Poly(ethene) / polyethene / polythene / HDPE / LDPE

M2 At higher pressures More / higher cost of electrical energy to pump / pumping cost OR Cost of higher pressure equipment / valves / gaskets / piping etc. OR expensive equipment

Credit all converse arguments for M2 2

(b) M1 for balanced equation

M2 for state symbols in a correctly balanced equation

2C(s / graphite) + 3H2(g) + ½O2(g) CH3CH2OH(l) (C2H5OH)

Not multiples but credit correct state symbols in a correctly balanced equation. Penalise C2H6O but credit correct state symbols in a correctly balanced equation.

2

(c) (i) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / element

If standard enthalpy of formation CE=0


M3 with (all) reactants and products / (all) substances in standard / specified states OR (all) reactants and products / (all) substances in normal states under standard conditions / 100 kPa / 1 bar and specified T / 298 K


3

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(ii) M1 Correct answer gains full marks

ΣB(reactants) − ΣB(products) = ΔH Credit 1 mark for (+) 1279 (kJ mol−1)

OR Sum of bonds broken − Sum of bonds formed = ΔH OR B(C-C) + B(C-O) + B(O-H) + 5B(C-H) + 3B(O=O) (LHS) − 4B(C=O) − 6B(O−H) (RHS) = ΔH

M2 (also scores M1) 348+360+463+5(412)+3(496) [LHS = 4719] (2060) (1488) − 4(805) − 6(463) [RHS = − 5998] = ΔH (3220) (2778) OR using only bonds broken and formed (4256 − 5535)

For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 2C and 6H and 7O OR a clear statement of M1 which could be in words and scores only M1

M3 ΔH= − 1279 (kJ mol−1)

Allow a maximum of one mark if the only scoring point is LHS = 4719 OR RHS = 5998

Award 1 mark for +1279

Candidates may use a cycle and gain full marks 3

(d) (i) Reducing agent OR reductant OR electron donor OR to reduce the copper oxide

Not “reduction”. Not “oxidation”. Not “electron pair donor”.

1

(ii) CH3COOH 1

[17]

Q13. (a) (Q = mcΔT)

= 50 × 4.18 × 27.3 If incorrect (eg mass = 0.22 or 50.22 g) CE = 0 / 2

1

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= 5706 J (accept 5700 and 5710) Accept 5.7 kJ with correct unit. Ignore sign.

1

(b) Mr of 2-methylpropan-2-ol = 74(.0) For incorrect Mr, lose M1 but mark on.

1

Moles = mass / Mr

= 0.22 / 74(.0)

= 0.00297 moles 1

ΔH = –5706 / (0.002970 × 1000)

= –1921 (kJ mol–1) If 0.22 is used in part (a), answer = –8.45 kJ mol–1 scores 3

(Allow –1920, –1919) If uses the value given (5580 J), answer = –1879 kJ mol–1 scores 3 Answer without working scores M3 only. Do not penalise precision. Lack of negative sign loses M3

1

(c) ΔH = ΣΔH products – ΣΔH reactants OR a correct cycle

Correct answer with no working scores 1 mark only. 1

ΔH = −(−360) + (4 × −393) + (5 × −286) M2 also implies M1 scored.

1

ΔH = –2642 (kJ mol–1) This answer only. Allow 1 mark out of 3 for correct value with incorrect sign.

1

(d) (–2422 – part (b)) × 100 / –2422 Ignore negative sign.

Expect answers in region of 20.7 If error carried forward, 0.22 allow 99.7 If 5580 J used earlier, then allow 22.4

1

(e) Reduce the distance between the flame and the beaker / put a sleeve around the flame to protect from drafts / add a lid / use a copper calorimeter rather than a pyrex beaker / use a food calorimeter

Any reference to insulating material around the beaker must be on top. Accept calibrate the equipment using an alcohol of known enthalpy of combustion.

1

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(f) Incomplete combustion 1

[11]

Q14. (a)

M1 C6H12O6 2CH3CH2OH (2C2H5OH)

+ 2CO2

Penalise C2H6O for ethanol in M1.

M2 and M3 Mark M2 and M3 independently.

Any two conditions in any order for M2 and M3 from

• (enzymes from) yeast or zymase

• 25 °C ≤ T ≤ 42 °C OR 298 K ≤ T ≤ 315 K

• anaerobic / no oxygen / no air OR neutral pH A lack of oxygen can mean either without oxygen or not having enough oxygen and does not ensure no oxygen, therefore only credit “lack of oxygen” if it is qualified. Penalise ‘bacteria’, ‘phosphoric acid’, ‘high pressure’ using the list principle.

M4 (fractional) distillation or GLC Ignore reference to ‘aqueous’ or ‘water’ (ie not part of the list principle).

M5 Carbon-neutral in this context means

There is no net / overall (annual) carbon dioxide / CO2 emission to the atmosphere

OR

There is no change in the total amount / level of carbon dioxide / CO2 present in the atmosphere

For M5 – must be about CO2 and the atmosphere. The idea that the carbon dioxide / CO2 given out equals the carbon dioxide / CO2 that was taken in from the atmosphere.

5

(b) M1 q = m c ∆T (this mark for correct mathematical formula) Full marks for M1, M2 and M3 for the correct answer. In M1, do not penalise incorrect cases in the formula.

M2 = (75 × 4.18 × 5.5)

1724 (J) OR 1.724 (kJ) OR 1.72 (kJ) OR 1.7 (kJ)

(also scores M1) Ignore incorrect units in M2.

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M3 Using 0.0024 mol

therefore ∆H = − 718 (kJ mol−1)

(Accept a range from −708 to −719 but do not penalise more than 3 significant figures)

Penalise M3 ONLY if correct numerical answer but sign is incorrect. Therefore +718 gains two marks. If units are quoted in M3 they must be correct. If ∆T = 278.5, CE for the calculation and penalise M2 and M3.

M4 and M5 in any order

Any two from

• incomplete combustion

• heat loss

• heat capacity of Cu not included

• some ethanol lost by evaporation

• not all of the (2.40 × 10−3 mol) ethanol is burned / reaction is incomplete If c = 4.81 (leads to 1984) penalise M2 ONLY and mark on for M3 = − 827

5

(c) (i) M1 enthalpy / heat / energy change (at constant pressure) or enthalpy / heat / energy needed in breaking / dissociating (a) covalent bond(s)

Ignore bond making.

M2 averaged for that type of bond over different / a range of molecules / compounds

Ignore reference to moles. 2

(ii) M1

∑ B(reactants) − ∑ B(products) = ∆H

OR

Sum of bonds broken − Sum of bonds formed = ∆H

OR

B(C-C) + B(C-O) + B(O-H) + 5B(C-H) + 3B(O=O) – 4B(C=O) – 6B(O–H) = ∆H = −1279

Correct answer gains full marks. Credit 1 mark for − 496 (kJ mol−1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2). If no AE, check for a correct method; this requires either a

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correct cycle with 2CO2 and 3H2O OR a clear statement of M1 which could be in words and scores only M1.

M2 (also scores M1) 348+360+463+5(412)+ 3B(O=O)

(3231) (or 2768 if O–H cancelled) − 4(805) − 6(463) = ∆H = − 1279

(5998) (or 5535 if O–H cancelled)

3B(O=O) = 1488 (kJ mol−1) Credit a maximum of one mark if the only scoring point is bonds formed adds up to 5998 (or 5535) OR bonds broken includes the calculated value of 3231 (or 2768).

M3

B(O=O) = 496 (kJ mol−1)

Award 1 mark for −496


[15]

Q15. (a) M1 (could be scored by a correct mathematical expression)

M1 ΔH = ΣΔHf (products) − ΣΔHf (reactants) OR a correct cycle of balanced equations

M2 = 5(−635) − (−1560)

= − 3175 + 1560


M3 = − 1615 (kJ mol−1) Award 1 mark ONLY for (+) 1615

Correct answer to the calculation gains all of M1, M2 and M3 Credit 1 mark for(+) 1615 (kJ mol−1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with V2O5 and 5CaO OR a clear statement of M1 which could be in words and scores only M1

M4 Type of reaction is • reduction • redox • (or accept) V2O5 / it / V(V) has been reduced

In M4 not “vanadium / V is reduced”

M5 Major reason for expense of extraction − the answer must be about

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calcium

Calcium is produced / extracted by electrolysis OR calcium is expensive to extract OR calcium extraction uses electricity OR calcium extraction uses large amount of energy OR calcium is a (very) reactive metal / reacts with water or air OR calcium needs to be extracted / does not occur native

QoL Accept calcium is expensive “to produce” but not “to source, to get, to obtain, to buy” etc. In M5 it is neither enough to say that calcium is “expensive” nor that calcium “must be purified”

5

(b) M1 2Al + Fe2O3 2Fe + Al2O3

Ignore state symbols Credit multiples of the equation

M2 (Change in oxidation state) 0 to (+)3 OR (changed by) +3

In M2 if an explanation is given it must be correct and unambiguous

2

(c) M1 VCl2 + H2 V + 2HCl

In M1 credit multiples of the equation

M2 and M3 Two hazards in either order

• HCl / hydrogen chloride / hydrochloric acid is acidic / corrosive / toxic / poisonous

• Explosion risk with hydrogen (gas) OR H2 is flammable For M2 / M3 there must be reference to hydrogen; it is not enough to refer simply to an explosion risk For M2 / M3 with HCl hazard, require reference to acid(ic) / corrosive / toxic only

M4 The only other product / the HCl is easily / readily removed / lost / separated because it is a gas OR will escape (or this idea strongly implied) as a gas OR vanadium / it is the only solid product (and is easily separated) OR vanadium / it is a solid and the other product / HCl is a gas

In M4 it is not enough to state simply that HCl is a gas, since this is in the question.

4 [11]

Q16. Increase in volume

If a volume is quoted it must be less than 300

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1

Smaller increase in T above room temperature Or increased contact between calorimeter and water Or smaller heat loss by evaporation / from the surface

1 [2]

Q17. (a) The enthalpy (change) to break 1 mol of H—O / bonds

Allow heat energy 1

Averaged over a range of compounds / molecules Penalise energy but mark on ignore states CE = 0 for ionic bonds

1

(b) H2 + O2 H2O

ΔH = (H−H) + (O = O) − 2(H−O) / sum of (bonds broken) − sum of (bonds formed)

1

= 436 + 496 / 2 − 2 × 464 1

= −244 (kJ mol−1) Allow 1 mark only for +244 and −488 Units not essential but penalise incorrect units

1

(c) (i) same reaction / same equation / same number / same reactants and same products / same number and type of bonds broken and formed

Do not allow similar 1

(ii) There must be a slight difference between the actual bond enthalpy (in water) and mean bond enthalpies for the O−H bond (in other molecules)

Allow bond enthalpy value for enthalpy of formation may not be under standard conditions. Allow reference to bond energy rather than bond enthalpy Do not allow heat loss or experimental error Do not allow mean bond enthalpies are not accurate

1 [7]

Q18. (a) M1 (q = mcΔT = 100 × 4.18 × 38(.0))

= 15 884 / 15 880 / 15 900 / 16 000 (J) (OR 15.884 / 15.88 / 15.9 / 16 (kJ))

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Award full marks for correct answer Mark is for value not expression (at least 2sf); penalise incorrect units here only if M1 is the only potential scoring point in M1-M3

1

M2 Moles (methanol = 1.65 / 32.0) = 0.0516 or 0.052 At least 2sf

1

M3 Heat change per moles = M1/M2 (15 884 / 0.0516 / 1000 = 308 (kJ mol−1) (allow 305 to 310)

At least 2sf; answer must be in kJ mol−1

1

M4 Answer = −308 (kJ mol−1) (allow −305 to −310) This mark is for – sign (mark independently)

1

(b) Heating up copper / calorimeter / container / thermometer / heat capacity of copper / calorimeter / thermometer not taken into account OR Evaporation of alcohol/methanol OR Experiment not done under standard conditions

Not human errors (e.g. misreading scales) Not impure methanol Allow evaporation of water

1

(c) (100 × 0.5 / 38 =) 1.3 or 1.32 or 1.316% (minimum 2 sf) Allow correct answer to at least 2sf; Allow 1.31 or 1.315%

1

(d) Idea that heat loss is more significant issue OR Idea that temperature change/rise is (significantly / much) bigger than uncertainty

One of these two ideas only and each one must involve a comparison

1

(e) M1 Mass of ethanol = 500 × 0.789 (= 394.5 or 395 (g)) 1

M2 Moles of ethanol = M1 / 46.0 (= 8.576 or 8.58) 1

M3 Heat released = M2 × 1371 = 11800 (kJ) must be 3 sf 1

Correct answer to 3sf scores 3; correct value to 2sf or more than 3sf scores 2 Answers that are a factor of 10x out score 2 if given to 3sf or 1 if given to a different number of sf M3 ignore units, but penalise incorrect units M3 ignore sign

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M2 and M3 – allow consequential marking [10]

Q19. (a) (i) 2C6H12O6 3CH3COCH3 + 3CO2 + 3H2O

Or multiples 1

(ii) to speed up the reaction OR (provide a) catalyst or catalyses the reaction or biological catalyst OR release / contain / provides an enzyme

Ignore “fermentation” Ignore “to break down the glucose” Not simply “enzyme” on its own

1

(b) (i) CH3CH(OH)CH3 + [O] CH3COCH3 + H2O Any correct representation for the two organic structures. Brackets not essential. Not “sticks” for the structures in this case

1

(ii) Secondary (alcohol) OR 2° (alcohol) 1

(c) M1 q = m c ΔT

OR q =150 × 4.18 × 8.0 Award full marks for correct answer In M1, do not penalise incorrect cases in the formula

M2 = (±) 5016 (J) OR 5.016 (kJ) OR 5.02 (kJ) (also scores M1)

M3 This mark is for dividing correctly the number of kJ by the number of moles and arriving at a final answer in the range shown.

Using 0.00450 mol

therefore ΔH = − 1115 (kJ mol−1 )

OR − 1114.6 to − 1120 (kJ mol−1 )

Range (+)1114.6 to (+)1120 gains 2 marks

BUT − 1110 gains 3 marks and +1110 gains 2 marks

AND − 1100 gains 3 marks and +1100 gains 2 marks Award full marks for correct answer In M1, do not penalise incorrect cases in the formula Penalise M3 ONLY if correct numerical answer but sign is incorrect; (+)1114.6 to (+)1120 gains 2 marks Penalise M2 for arithmetic error and mark on If ΔT = 281; score q = m c ΔT only

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If c = 4.81 (leads to 5772) penalise M2 ONLY and mark on for M3 = − 1283 Ignore incorrect units in M2 If units are given in M3 they must be either kJ or kJ mol−1 in this case

3

(d) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / element


M3 with (all) reactants and products / (all) substances in standard / specified states

OR (all) reactants and products / (all) substances in normal states under standard conditions / 100 kPa / 1 bar and specified T / 298 K


3

(e) M1 Σ B (reactants) − Σ B (products) = ΔH OR Sum of bonds broken − Sum of bonds formed = ΔH OR 2B(C−C) + B(C=O) + 6B(C−H) + 4B(O=O) (LHS)

− 6B(C=O) − 6B(O−H) (RHS) = ΔH

M2 (also scores M1) 2(348)+805+6(412)+4(496) [LHS = 5957]

(696) (2472) (1984)

− 6(805) − 6(463) [RHS = (−) 7608] = ΔH

(4830) (2778)

OR using only bonds broken and formed (5152 − 6803)

M3 ΔH= − 1651 (kJ mol−1)

Candidates may use a cycle and gain full marks. Correct answer gains full marks Credit 1 mark for (+) 1651 (kJ mol−1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication / addition error; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 4O2, 3CO2 and 3H2O OR a clear statement of M1 which could be in words and scores only M1

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Allow a maximum of one mark if the only scoring point is LHS = 5957 (or 5152) OR RHS = 7608 (or 6803) Award 1 mark for + 1651

3

(f) For the two marks M1 and M2, any two from • heat loss or not all heat transferred to the apparatus or heat absorbed by

the apparatus or (specific) heat capacity of the apparatus not considered • incomplete combustion / not completely burned / reaction is not complete • The idea that the water may end up in the gaseous state (rather than

liquid) • reactants and / or products may not be in standard states. • MBE data refers to gaseous species but the enthalpy of combustion refers

to liquids in their standard states / liquid propanone and liquid water in standard states

• MBE do not refer to specific compounds OR MBE values vary with different compounds / molecules OR are average / mean values taken from a range of compounds / molecules

Apply the list principle but ignore incomplete reasons that contain correct chemistry Ignore “evaporation” Ignore “faulty equipment” Ignore “human error” Not enough simply to state that “MBE are mean / average values”

2 [15]

Q20. (a) The enthalpy / heat energy change when 1 mol (of a substance)

If enthalpy of formation definition given CE=O NOT just ‘energy’ ALLOW alternatives for substance e.g. molecule/compound/element

1 Is burned/reacts completely in oxygen

ALLOW reacts in excess oxygen 1

With all reactants and products in their standard states OR With all reactants and products in their normal states at 298K/given temp & 100kPa

ALLOW ‘everything’ for ‘reactants and products’ Penalise incorrect conditions if given ALLOW ‘normal states under standard conditions’

1

(b) ∆H = Σ∆Hc(reactants) - Σ∆Hc (products) OR Correctly and fully balanced cycle

Correct answer scores 3 1

∆H = [3(-394) + 4(-286)] – (-2010) OR

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∆H = -2326 + 2010 M2 also scores M1

1 ∆H = -316 (kJ mol-1) +316 scores 1 mark only

IGNORE units Check for AE in working – can award M3 as ecf (error carried forward) from M2 if M2 not given due to AE

1

(c) ∆H/-1893 = ΣB(reactants) - ΣB(products) OR ∆H/-1893 = ΣBonds broken - ΣBonds formed OR ∆H/-1893 = 2B(C-C) + 7B(C-H) + B(C-O) + B(O-H) + 4½ B(O=O) – 6B(C=O) – 8B(O-H)

Correct answer scores 3 1

-1893= 2B(C-C) + 7(412) + 360 + 463 + 4½(496) – 6(805) – 8(463) OR -1893= 2B(C-C) +5939 – 8534 OR -1893= 2B(C-C) -2595 OR 2B(C-C) = 702

M2 also scores M1 May see no 463 in bonds broken and 7x463 in made (gives 5476 – 8071)

1 B(C-C) = (+)351(kJ mol-1)

If NOT 351 check for AE. This would lose M2, but could gain M1 and M3 (+)234 scores 1 (due to 3(C-C)) NOT M3 from incorrect M2 unless incorrect M2 is due to AE IGNORE units If no other mark awarded then ALLOW 1 if 5939 or 5476 or 8534 or 8071 seen

1 [9]

Q21. B

[1]

Q22. (a) Weigh the spirit burner (alcohol) before and after combustion M1

Do not allow “a known mass of alcohol” owtte 1

Water in a calorimeter / beaker M2 1

Measure volume of water (or mass) M3 1

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Burn the alcohol to heat the water M4 1

Measure temperature rise in water M5 1

(b) Incomplete combustion

Evaporation of alcohol

Heat capacity of / heat absorption by the apparatus

Inadequate stirring Any two correct

1 1

(c) Acidified potassium dichromate / manganate(VII) (Heat) Allow sodium in place of potassium with appropriate colour change) If reagent incomplete lose M1 but mark on. If reagent incorrect, CE = 0/3

1

butan-1-ol orange to green / purple to colourless 1

2-methylpropan-2-ol NVC / orange / purple 1

(d) C4H9OH + 2O2 → 4C + 5H2O OR C4H9OH + 4O2 → 4CO + 5H2O

Allow any correct balanced equations which include combinations of C, CO and/or CO2 in the products but must be incomplete combustion.

1

Engine would not run as efficiently / would need to use more fuel / would release less energy

Allow build-up of carbon in engine costly to remove 1

CO / Particulates of carbon toxic Allow global dimming if carbon given as product

1 [13]

Q23. (a) Start a clock when KCl is added to water

1

Record the temperature every subsequent minute for about 5 minutes Allow record the temperature at regular time intervals until some time after all the solid has dissolved for M2

1

Plot a graph of temperature vs time

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1

Extrapolate back to time of mixing = 0 and determine the temperature 1

(b) Heat taken in = m × c × ΔT = 50 × 4.18 × 5.4 = 1128.6 J Max 2 if 14.6 °C used as ΔT

1

Moles of KCl = 5.00 / 74.6 = 0.0670 1

Enthalpy change per mole = +1128.6 / 0.0670 = 16 839 J mol-1

1

= +16.8 (kJ mol-1) Answer must be given to this precision

1

(c) ΔHsolution = ΔHlattice + ΔH(hydration of calcium ions) + 2 × ΔH(hydration of chloride ions)

ΔHlattice = ΔHsolution – ΔH(hydration of calcium ions) –2 ×ΔH(hydration of chloride ions)

1

ΔHlattice = –82–9 – (–1650 + 2 × –364) = +2295 (kJ mol–1) 1

(d) Magnesium ion is smaller than the calcium ion 1

Therefore, it attracts the chloride ion more strongly / stronger ionic bonding 1

[12]

Q24. (a) C(s) + 2F2(g) CF4(g)

State symbols essential 1

(b) Around carbon there are 4 bonding pairs of electrons (and no lone pairs) 1

Therefore, these repel equally and spread as far apart as possible 1

(c) ΔH = Σ ΔfH products – Σ ΔfH reactants or a correct cycle 1

Hence = (2 × –680) + (6 × –269) – (x) = –2889 1

x = 2889 – 1360 – 1614 = –85 (kJ mol–1) 1

Score 1 mark only for +85 (kJ mol–1)

(d) Bonds broken = 4(C–H) + 4(F–F) = 4 × 412 + 4 × F–F

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Bonds formed = 4(C–F) + 4(H–F) = 4 × 484 + 4 × 562 Both required

1

–1904 = [4 × 412 + 4(F–F)] – [4 × 484 + 4 × 562]

4(F–F) = –1904 – 4 × 412 + [4 × 484 + 4 × 562] = 632 1

F–F = 632 / 4 = 158 (kJ mol–1) 1

The student is correct because the F–F bond energy is much less than the C–H or other covalent bonds, therefore the F–F bond is weak / easily broken

Relevant comment comparing to other bonds (Low activation energy needed to break the F–F bond)

1 [10]

Q25. (a) Bonds broken = 2(C=O) + 3(H–H) = 2 × 743 + 3 × H–H

Bonds formed = 3(C–H) +(C–O) + 3(O–H) = 3 × 412 + 360 + 3 × 463 Both required

1

–49 = [2 × 743 + 3 × (H–H)] – [3 × 412 + 360 + 3 × 463]

3(H–H) = –49 – 2 × 743 + [3 × 412 + 360 + 3 × 463] = 1450 Both required

1

H–H = 483 (kJ mol–1) Allow 483.3(3)

1

(b) Mean bond enthalpies are not the same as the actual bond enthalpies in CO2 (and / or methanol and / or water)

1

(c) The carbon dioxide (produced on burning methanol) is used up in this reaction 1

(d) 4 mol of gas form 2 mol 1

At high pressure the position of equilibrium moves to the right to lower the pressure / oppose the high pressure

1

This increases the yield of methanol 1

(e) Impurities (or sulfur compounds) block the active sites Allow catalyst poisoned

1

(f) Stage 1: moles of components in the equilibrium mixture

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Extended response question

CO2(g) + 3H2(g) CH3OH(g) + H2O(g)

Initial moles 1.0 3.0 0 0

Eqm moles

(1–0.86) = 0.14

(3–3×0.86) = 0.42 0.86 0.86

1

Stage 2: Partial pressure calculations

Total moles of gas = 2.28

Partial pressures = mol fraction × ptotal 1

pCO2 = mol fraction × ptotal = 0.14 × 500 / 2.28 = 30.7 kPa

pH2 = mol fraction × ptotal = 0.42 × 500 / 2.28 = 92.1 kPa M3 is for partial pressures of both reactants Alternative M3 = ppCO2 = 0.0614 × 500 ppH2 = 0.1842 × 500

1

pCH3OH = mol fraction × ptotal = 0.86 × 500 / 2.28 = 188.6 kPa

pH2O = mol fraction × ptotal = 0.86 × 500 / 2.28 = 188.6 kPa M4 is for partial pressures of both products Alternative M4 = ppCH3OH = 0.3772 × 500 ppH2O = 0.3772 × 500

1

Stage 3: Equilibrium constant calculation Kp = pCH3OH × pH2O / pCO2 × (pH2)3

1

Hence Kp = 188.6 × 188.6 / 30.7 × (92.1)3 = 1.483 × 10–3 = 1.5 × 10–3

Answer must be to 2 significant figures 1

Units = kPa–2

1 [16]

Q26.

(a) C6H11OH + 6CO2 + 6H2O 1

(b) Temperature rise = 20.1

q = 50.0 × 4.18 × 20.1 = 4201 (J)

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1

Mass of alcohol burned = 0.54 g and Mr alcohol = 100.0

∴ mol of alcohol = n = 0.54 / 100 = 0.0054 1

Heat change per mole = q / 1000n OR q / n

= 778 kJ mol–1 OR 778 000 J mol–1

1

ΔH = –778 kJ mol–1 OR –778 000 J mol–1

M4 is for answer with negative sign for exothermic reaction Units are tied to the final answer and must match

1

(c) Less negative than the reference 1

Heat loss OR incomplete combustion OR evaporation of alcohol OR heat transferred to beaker not taken into account

1

(d) Water has a known density (of 1.0 g cm–3) 1

Therefore, a volume of 50.0 cm3 could be measured out 1

[9]

Q27. C

[1]

Q28. B

[1]

Q29. (a) Decrease

1

Increasing pressure moves equilibrium to the side of least moles i.e. backward reaction

1

To oppose the increase in pressure or to decrease the pressure 1

(b) A catalyst speeds up the rate of the forward and backward reaction 1

By the same amount 1

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(c) ΔH = −111 − (−75 − 242) 1

206 (kJ mol−1) 1

(d) ΔS = 3 × 131 + 198 − (186 + 189) = 216 J K−1 mol−1

1

ΔG = ΔH − TΔS 1

0 = 206 − T 1

T = 953.7 or 954 K 1

T = 681 (°C) If the value given in the question is used then the answer is 283 (°C)

1 [12]

Q30. TWO correct extrapolations of best fit straight lines

Max 5/7 if no extrapolations or best fit straight lines drawn

1

Use of their lines to calculate the temperature change at the 4th minute 1

(17 °C)

Q = mcΔT

Q = 10 × 4.18 × [student’s temperature change]

Q = [710.6 J] Correct numbers inserted into expression.

1

Moles of Mg = 0.24 / 24.3 = 0.00988 mol 1

ΔH = 710.6 / 0.00988 = 71923.07 J mol−1

1

ΔH = –72 (kJ mol−1) Must be negative to score M6

1

Answer to 2 significant figures 1

[7]

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Q31. (a) 2Fe(s) + O2(g) ⟶ Fe2O3(s) ONLY

Don’t allow multiples. States must be shown 1

(b) M1 Correct cycle or equation If M1 and M2 not awarded then M3 can be awarded for their M2 divided by 3

1 M2 (3 × ΔfHCO2) = −19 + (−822) + 3(−111) − 0 (3 × ΔfHCO2) = −1174

1 M3 ΔfHCO2 = −391  kJ mol−1

−317 for 1 mark +391 for 1 mark

1

Allow 2 sig fig or more

(c) M1 Correct Hess’s law cycle or equation If M1 and M2 not awarded then M3 can be awarded for their M2 divided by 6

1 M2 (6(N−H)) = 944 + 3(+436) + 92 (6(N−H)) = 2344

−391 for 1 mark 1

M3 N−H = (+)391 kJ mol−1

1

Allow 2 sig fig or more

(d) Data book value derived from (a number of) different compounds (not just different NH3 molecules)

1 [8]

Q32. (a) Not possible to prevent some dissolving

ALLOW It is soluble / dissolves / other hydrates may form / suggestions related to difficulty of measuring T (change) of a solid

1

(b) (ΔhydH =) –155 – (–39) OR labelled cycle Minimum needed for ‘labelled cycle’

1

–116 (kJ mol−1) 1/2 for (+)116 or for –29 or for seeing –116 that has then be

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processed further 1

(c) This question is marked using levels of response. Refer to the Mark Scheme Instructions for examiners for guidance on how to mark this question

Level 3 (5 – 6 marks)

All stages are covered and the explanation of each stage is correct and virtually complete. Stage 2 must include use of a graphical method for Level 3 (i.e. ‘highest T reached’ method is max Level 2)

Answer communicates the whole explanation, including reference to enthalpy, coherently and shows a logical progression through all three stages.Answer is full and detailed and is supported by an appropriate range of relevant points such as those given below: For the answer to be coherent there must be some indication of how the graph is used to find ΔT


All stages are covered (NB ‘covered’ means min 2 from each of stage 1 and 3) but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages covered and the explanations are generally correct and virtually complete

Answer is coherent and shows some progression through all three stages. Some steps in each stage may be out of order and incomplete


Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR only one stage is covered but the explanation is generally correct and virtually complete

Answer shows some progression between two stages

Level 0 (0 marks)

Insufficient correct Chemistry to warrant a mark

Indicative Chemistry Content

Stage 1 Method

(1a) Measures water with named appropriate apparatus (1b) Suitable volume/mass / volume/mass in range 10 – 200 cm3/g (1c) Into insulated container / polystyrene cup (NOT just ‘lid’) (1d) Add known mass of MgCl2(s) (1e) Use of ‘before and after’ weighing method. NOT ‘added with washings’

Stage 2 Measurements (could mark from diagram)

(2a) Record initial temperature (min 2 measurements) (2b) Record T at regular timed intervals for 5+ mins / until trend seen (2c) Plot T vs time

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Stage 3 Use of Results (3a and 3b could come from diagram)

(3a) Extrapolate lines to when solid added (to find initial and final T) (3b) Tfinal – Tinitial = ΔT / idea of finding ΔT from graph at point of addition (3c) q = mcΔT (3d) amount = mass/Mr (0.80/95.3 = 8.39 × 10−3 mol) (3e) ΔHsoln = –q/8.39 × 10−3 or in words

This could all be described in words without showing actual calculations but describing stages

If method based on ‘combustion’ Max Level 1 6

(d)

M1 = 5 points correctly plotted M2 = line drawn correctly (NOT if curved, doubled or kinked) (Check line of best fit – if through 250, -600.5 and 280, -595.5 +/- one small square then award M2, if all crosses on line award M1 as well)

2

Gradient = Δ(ΔG)/ΔT = 0.167 (kJ K−1 mol−1) 1

(ΔG = ΔH – TΔS so gradient = –ΔS)

ΔS = –167 (J K−1 mol−1) M4 = unit conversion i.e. M3 × 1000; M5 = –sign (process marks) Correct answer with sign gets M3, M4 and M5 ALLOW –163 to –171

1+1 [14]

Q33. (a) C2H5OH(I) + 3O2(g) ⟶ 2CO2(g) + 3H2O(I)

1 mark for correct formulae and balancing

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1

1 mark for all correct state symbols 1

(b) (Standard) enthalpy of formation 1

Difficult to prevent C reacting with O2 to form some CO2 1

(c) ΔH = ΣΔHc reactants − ΣΔHc products or a correct cycle 1

OR ΔH = −393−(−283)

ΔH = −110 (kJ mol−1)

1

(d) Correctly drawn Hess’s law cycle 1

4 (Xe–F) = 252 + (2 × 158) = 568

Xe–F = 568 / 4 1

Xe–F = 142 (kJ mol−1)) 1

(e) Mean bond enthalpy found by taking an average for Xe–F in a range of compounds

1 [10]

Q34. (a) M1 Amount ZnSO4 = 1.0 × mol or Amount ZnSO4 = 0.050 mol

Mark M1 and M2 independently 1

M2 Amount Mg = mol or Amount Mg = 0.0856 mol (Hence Mg in excess)

1 M3 Q = mcΔT

M3 could be scored in M4 1

M4 Q = 50.0 × 4.18 × 37.3 or Q = 7795.7 J

If an error in M4, lose M4 and M5 and only award M6 for correct use of their incorrect M4 and division by their correct limiting reagent

1

M5 (Energy released per mole) kJ mol−1 or J mol−1

M5 division by their limiting reagent 1

M6 ΔH = − 156 kJ mol−1

1

(b) Heat loss (from the apparatus would mean the experimental value is smaller /

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lower / less exothermic than the data source) 1

(c) Marks awarded for this answer will be determined by the quality of the communication as well as the standard of the scientific response. Examiners should apply a ‘best-fit’ approach to the marking.

Level 3 (5 – 6 marks) Covers 3 Stages with matching justifications Answer is full and detailed and is supported by an appropriate range of relevant points such as those given below: • argument is well structured with minimum repetition or irrelevant points • accurate and clear expression of ideas with only minor errors in the use of

technical terms, spelling and punctuation and grammar

Level 2 (3 – 4 marks) Covers 2 Stages with matching justification. OR covers 3 Stages with incomplete justification Answer has some omissions but is generally supported by some of the relevant points below: • the argument shows some attempt at structure • the ideas are expressed with reasonable clarity but with a few errors in the

use of technical terms, spelling, punctuation and grammar

Level 1 (1 – 2 marks) Covers 1 Stage with matching justification. OR covers 2 Stages with incomplete justification Answer is largely incomplete. It may contain valid points which are not clearly linked to an argument structure. Unstructured answer. Errors in the use of technical terms, spelling, punctuation and grammar or lack of fluency

Level 0 (0 marks)

Insufficient correct chemistry

Indicative Chemistry Content

Stage 1 Improved insulation 1a Insulate the beaker or use a polystyrene cup or a lid 1b To reduce heat loss

Stage 2 Improved temperature recording 2a Record the temperature for a suitable time before adding the metal 2b To establish an accurate initial temperature OR 2c Record temperature values at regular time intervals 2d To plot the temperature results against time on a graph

Stage 3 Improved analysis of results 3a Extrapolate the cooling back to the point of addition 3b To establish a (theoretical) maximum temperature OR temperature change (e.g. at the 4th minute) OR adjust for the cooling /apply a cooling correction 3a and 3b could be seen on an extrapolated sketch graph

(Note– IGNORE use of measuring equipment with greater precision) 6

[13]

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Q35. (a) C3H8 + 5O2 ⟶ 3CO2 + 4H2O

allow fractions / multiples allow any correct structural representation of molecules ignore state symbols

1

(b) M1 working that leads to n = 13 e.g. −6650 = −(496n + 202) and/or 496n = 6650 − 202 and/or 496n = 6448 (n = 13)

1

M2 C13H28

C13H28 scores M1 and M2 if some correct working shown C13H28 with no working scores M2 only allow error carried forward for M2 for a correct formula of an alkane from the value of n worked out for M1 (but there must be some working shown leading to this incorrect value of n); for example, allow C14H30 if error in M1 stemming from error in rearranging equation

1

(c) Idea that • alkane is not gaseous or • equation relates to gaseous alkanes or • it takes energy to convert it into a gas or • that water / alkane / substances are gaseous in calculations using bond enthalpies

ignore references to heat loss, incomplete combustion, loss of evaporation, not being in standard conditions or that it is not standard state

1

(d) M1 plotting the four values correctly (allow one error where point is ±1 square out)

If plotted points for wrong number of C atoms for two or more compounds, cannot score M1 or M2, but could score M3 if read value off for 3C atoms

1 M2 smooth best fit curve

M2 best fit curve for their four points for the correct number of C atoms

1 M3 value from their best fit line for 3 C atoms (allow ± 1 square)

M3 need – sign (but ignore units); cannot score M3 unless there is a line on the graph

1

(e) M1 mass of isooctane = 692 (g) correct answer scores M1 and M2

1 M2 3.31 × 104 or 33100 (kJ) (3sf only)

M2 correct value to incorrect number of sig figs is 1 mark;

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ignore sign ; no error carried forward for M2

1 [9]

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Energetics exam pack 2

Name: ________________________

Class: ________________________

Date: ________________________

Time: 252 minutes

Marks: 248 marks

Comments:

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Q1. (a) Define the term standard enthalpy of formation, ∆Hfο

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Use the data in the table to calculate the standard enthalpy of formation of liquid methylbenzene, C7H8

Substance C(s) H2(g) C7H8(l)

Standard enthalpy of combustion, ∆Hcο /kJ mol–1 –394 –286 –3909

7C(s) + 4H2(g) → C7H8(l)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) An experiment was carried out to determine a value for the enthalpy of combustion of liquid methylbenzene using the apparatus shown in the diagram.

Burning 2.5 g of methylbenzene caused the temperature of 250 g of water to rise by 60°C. Use this information to calculate a value for the enthalpy of combustion of methylbenzene, C7H8

(The specific heat capacity of water is 4.18 J K–1 g–1. Ignore the heat capacity of the container.)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(d) A 25.0 cm3 sample of 2.00 mol dm–3 hydrochloric acid was mixed with 50.0 cm3 of a

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1.00 mol dm–3 solution of sodium hydroxide. Both solutions were initially at 18.0 °C.

After mixing, the temperature of the final solution was 26.5°C.

Use this information to calculate a value for the standard enthalpy change for the following reaction.

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

In your calculation, assume that the density of the final solution is 1.00 g cm–3 and that its specific heat capacity is the same as that of water. (Ignore the heat capacity of the container.)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(e) Give one reason why your answer to part (d) has a much smaller experimental error than your answer to part (c).

___________________________________________________________________

___________________________________________________________________ (1)

(Total 15 marks)

Q2. Using the data below, which is the correct value for the standard enthalpy of formation for TiCl4(l)?

C(s) + TiO2(s) + 2Cl2(g) → TiCl4(l) + CO2(g) ∆H = −232 kJ mol−1

Ti(s) + O2(g) → TiO2(s) = −912 kJ mol−1

C(s) + O2(g) → CO2(g) = −394 kJ mol−1

A −1538 kJ mol−1

B −1094 kJ mol−1

C −750 kJ mol−1

D +286 kJ mol−1

(Total 1 mark)

Q3. (a) State what is meant by the term mean bond enthalpy.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (2)

(b) Ethanal has the structure

Gaseous ethanal burns as shown by the equation

CH3CHO(g) + 2½O2(g) → 2H2O(g) + 2CO2(g)

Use the mean bond enthalpy data given below to answer the following questions.

Bond Mean bond enthalpy/kJ mol–1

C—H +413

C—C +347

C==O +736

O==O +498

O—H +464

(i) Calculate the enthalpy change which occurs when all the bonds in the reactants shown in the above equation are broken.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(ii) Calculate the enthalpy change which occurs when all the bonds in the products shown in the above equation are formed.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(iii) Hence, calculate the enthalpy change for the complete combustion of ethanal as shown in the equation above.

______________________________________________________________

______________________________________________________________ (5)

(Total 7 marks)

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Q4. A 50.0 cm3 sample of a 0.200 mol dm–3 solution of silver nitrate was placed in a polystyrene beaker. An excess of powdered zinc was added to this solution and the mixture stirred. Zinc nitrate, Zn(NO3)2, and silver were formed and a rise in temperature of 3.20 °C was recorded.

(a) Write an equation for the reaction between silver nitrate and zinc.

___________________________________________________________________ (1)

(b) Calculate the number of moles of silver nitrate used in the experiment.

___________________________________________________________________

___________________________________________________________________ (2)

(c) Calculate the heat energy evolved by the reaction in this experiment assuming that all the energy evolved is used to heat only the 50.0 g of water in the mixture. (Specific heat capacity of water is 4.18 J g–1 K–1)

___________________________________________________________________

___________________________________________________________________ (2)

(d) Calculate the heat energy change for the reaction per mole of zinc reacted.

___________________________________________________________________

___________________________________________________________________ (2)

(e) Explain why the experimental value for the heat energy evolved in this experiment is less than the correct value.

___________________________________________________________________

___________________________________________________________________ (1)

(Total 8 marks)

Q5. (a) Define the term standard molar enthalpy of formation, ΔHf .

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) State Hess’s law.

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___________________________________________________________________

___________________________________________________________________ (1)

(c) Propanone, CH3COCH3, burns in oxygen as shown by the equation

CH3COCH3(l) + 4 O2(g) → 3H2O(l) + 3CO2(g)

Use the data given below to calculate the standard enthalpy of combustion of propanone.

CO2(g) H2O(l) CH3COCH3(l)

ΔHf /kJ mol–1 –394 –286 –248

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 7 marks)

Q6. (a) What is the meaning of the term enthalpy change?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) (i) Define the term standard enthalpy of formation of a compound.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(ii) Write an equation, including state symbols, for the formation from its elements of solid sodium sulphate, Na2SO4

______________________________________________________________ (5)

(c) State Hess’s Law.

___________________________________________________________________

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___________________________________________________________________ (1)

(d) Some standard enthalpy changes are difficult to measure directly but can be determined from standard enthalpies of combustion. Maleic acid, C4H4O4, reacts with oxygen to form carbon dioxide and water as shown by the following equation.

C4H4O4(s) + 3O2(g) → 4CO2(g) + 2H2O(l)

Use the standard enthalpy of combustion data given below to calculate a value for the standard enthalpy change for the following reaction.

4C(s) + 2H2(g) + 2O2(g) → C4H4O4(s)

C4H4O4(s) C(s) H2(g)

ΔHcθ / kJ mol–1 –1356 –393.5 –285.8

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 11 marks)

Q7. The data below refer to the industrial production of nitric acid from ammonia.

Reaction 1 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) ∆H = −909 kJ mol−1

Reaction 2 2NO(g) + O2(g) 2NO2(g) ∆H = −115 kJ mol−1

Reaction 3 3NO2(g) + H2O(l) 2HNO3(aq) + NO(g) ∆H = −117 kJ mol−1

The direct oxidation of ammonia to nitrogen dioxide can be represented by the equation

4NH3(g) + 7O2(g) → 4NO2(g) + 6H2O(g)

for which the standard enthalpy change, in kJ mol−1, is

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A −1139

B −1024

C −794

D −679 (Total 1 mark)

Q8. The table below contains some mean bond enthalpy data.

Bond H––H C––C C=C N≡N N––H

Mean bond enthalpy / kJ mol–1 436 348 612 944 388

(a) Explain the term mean bond enthalpy.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) (i) Write an equation for the formation of one mole of ammonia, NH3, from its elements.

______________________________________________________________

(ii) Use data from the table above to calculate a value for the enthalpy of formation of ammonia.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (4)

(c) Use the following equation and data from the table above to calculate a value for the C–H bond enthalpy in ethane.

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (3)

(Total 9 marks)

Q9. Using the information below, answer this question.

Fe2O3(s) + 3H2(g) → 2Fe(s) + 3H2O(g) ΔH = +96 kJ mol−1, ΔS = +138 J K−1 mol−1

Fe2O3(s) H2(g) Fe(s)

ΔH / kJ mol−1 −822.0 0 0

ΔS / J K−1 mol−1 90.0 131.0 27.0

The standard enthalpy of formation of steam is

A +286 kJ mol−1

B +242 kJ mol−1

C −242 KJ mol−1

D −286 kJ mol−1

(Total 1 mark)

Q10. (a) Write an equation for the complete combustion of propanone, C3H6O, to form carbon

dioxide and water.

___________________________________________________________________ (1)

(b) In a laboratory experiment, 1.45 g of propanone were burned completely in oxygen. The heat from this combustion was used to raise the temperature of 100 g of water from 293.1 K to 351.2 K.

(i) Calculate the number of moles of propanone in the 1.45 g.

______________________________________________________________

______________________________________________________________

(ii) Calculate the heat energy required to raise the temperature of 100 g of water from 293.1 K to 351.2 K. (The specific heat capacity of water is 4.18 J K–1 g–1)

______________________________________________________________

______________________________________________________________

______________________________________________________________

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______________________________________________________________

(iii) Hence, calculate a value, in kJ mol–1, for the enthalpy of combustion of propanone.

______________________________________________________________

______________________________________________________________ (5)

(c) In a similar experiment, the enthalpy of combustion of butanone, C4H8O, was found to be –1290 kJ mol–1. A data book value for the same reaction is ΔHc = –2430 kJ mol–1.

(i) Suggest one reason why the experimental value is very different from the data book value.

______________________________________________________________

(ii) This data book value of ΔHc for butanone (–2430 kJ mol–1) refers to the formation of carbon dioxide gas and water in the gaseous state. How would this value differ if it referred to the formation of water in the liquid state? Explain your answer.

Difference _____________________________________________________

Explanation ____________________________________________________

______________________________________________________________ (3)

(d) Calculate a value for the standard enthalpy of formation for liquid ethanethiol,C2H5SH. Use the equation given below and enthalpy of combustion data from the following table.

Substance C2H5SH(l) C(s) H2(g) S(s)

ΔHc / kJ mol–1 –1170 –394 –286 –297

2C(s) + 3H2(g) + S(s) → C2H5SH(l)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 12 marks)

Q11. (a) Define the term standard enthalpy of formation.

(3)

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(b) State Hess’s Law and use it, together with the data given in the table below, to calculate the standard enthalpy change for the following reaction.

MgO(s) + 2HCl(g) → MgCl2(s) + H2O(l)

MgO HCl(g) MgCl2 H2O

ΔHf /kJ mol–1 –602 –92 –642 –286

(4)

(c) In an experiment, an excess of solid magnesium oxide was added to 50 cm3 of 3.0 mol dm–3 hydrochloric acid. The initial temperature of the solution was 21 °C. After reaction, the temperature had risen to 53 °C. (The specific heat capacity of water is 4.2 J K–1 g–1)

Use this information to calculate the enthalpy change for the reaction of one mole of magnesium oxide with hydrochloric acid. For your calculation you should assume that all the heat from the reaction is used to raise the temperature of 50 g of water.


Q12. Use the information below to answer this question.

C(s) + O2(g) → CO2(g) ∆H = −393.5 kJ mol−1

H2(g) + O2(g) → H2O(l) ∆H = −285.8 kJ mol−1

3C(s) + 4H2(g) → C3H8(g) ∆H = −104.0 kJ mol−1

4C(s) + 5H2(g) → C4H10(g) ∆H = −125.2 kJ mol−1

The value in kJ mol−1 for the enthalpy of combustion of propane is

A −211.7

B −419.7

C −2220

C −2878 (Total 1 mark)

Q13. Consider the reactions

C2H4(g) + 2O2(g) → 2CO(g) + 2H2O(g) ∆H = −758 kJ mol−1

2C(s) + 2H2(g) → C2H4(g) ∆H = +52 kJ mol−1

H2(g) + O2(g) → H2O(g) ∆H = −242 kJ mol−1

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The enthalpy of formation of carbon monoxide is

A −111 kJ mol−1

B −163 kJ mol−1

C −222 kJ mol−1

D -464 kJ mol−1

(Total 1 mark)


C(s) + O2(g) → CO2(g) ∆H = −393.5 kJ mol−1

H2(g) + O2(g) → H2O(l) ∆H = −285.8 kJ mol−1

3C(s) + 4H2(g) → C3H8(g) ∆H = −104.0 kJ mol−1

4C(s) + 5H2(g) → C4H10(g) ∆H = −125.2 kJ mol−1

The value in kJ mol−1 of the enthalpy of thermal dissociation when butane forms propane, hydrogen and carbon is

A −26.3

B −17.5

C +17.5

C +21.2 (Total 1 mark)

Q15. Given the following data

C(s) + 2H2(g) → CH4(g) ∆H = −75 kJ mol−1

H2(g) → 2H(g) ∆H = +436 kJ mol−1

which one of the following is the enthalpy change, in kJ mol−1, of the reaction below?

CH4(g) → C(s) + 4H(g)

A −947

B +511

C +797


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Q16. In which one of the following reactions is the standard enthalpy change equal to the standard enthalpy of formation of lithium fluoride?

A Li(g) + F(g) → LiF(s)

B Li+(g) + F−(g) → LiF(s)

C Li+(aq) + F−(g) → LiF(s)

D Li(s) + F2(g) → LiF(s) (Total 1 mark)


C(s) + O2(g) → CO2(g) ΔH = −394 kJ mol−1

H2(g) + O2(g) → H2O(l) ΔH = −286 kJ mol−1

4C(s) + 5H2(g) → C4H10(g) ΔH = −126 kJ mol−1

The standard enthalpy of combustion of butane, in kJ mol−1, is

A −2880

B −2590

C −806


Q18. (a) The table below contains some mean bond enthalpy data.

Bond H–O O–O O=O

Mean bond enthalpy/kJ mol–1 463 146 496

The bonding in hydrogen peroxide, H2O2, can be represented by H–O–O–H. Use these data to calculate the enthalpy change for the following reaction.

H2O2(g) → H2O2(g) + O2(g)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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(3)

(b) The standard enthalpy of formation, ΔHf for methane, is –74.9 kJ mol–1. Write an equation, including state symbols, for the reaction to which this enthalpy change applies.

___________________________________________________________________ (2)

(c) The enthalpy changes for the formation of atomic hydrogen and atomic carbon from their respective elements in their standard states are as follows.

H2(g) → H(g) ΔH = +218 kJ mol–1

C(s) → C(g) ΔH = +715 kJ mol–1

(i) By reference to its structure, suggest why a large amount of heat energy is required to produce free carbon atoms from solid carbon.

______________________________________________________________

______________________________________________________________

(ii) Parts (b) and (c) give enthalpy data for the formation of CH4(g), H(g) and C(g). Use these data and Hess’s Law to calculate the value of the enthalpy change for the following reaction.

CH4(g) → C(g) + 4H(g)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(iii) Use your answer from part (c)(ii) to calculate a value for the mean bond enthalpy of a C–H bond in methane.

______________________________________________________________ (5)

(Total 10 marks)

Q19. When ethanamide (CH3CONH2) burns in oxygen the carbon is converted into carbon dioxide, the hydrogen is converted into water and the nitrogen forms nitrogen gas.

Substance ethanamide carbon dioxide

water

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Enthalpy of formation ( ) / kJ mol−1

−320 −394 −286

Using the data above, which one of the following is a correct value for the enthalpy of combustion of ethanamide?

A −1823 kJ mol−1

B −1183 kJ mol−1

C −1000 kJ mol−1

D −360 kJ mo1−1

(Total 1 mark)

Q20. This question is about the reaction given below.

CO(g) + H2O(g) CO2(g) + H2(g)

Enthalpy data for the reacting species are given in the table below.

Substance CO(g) H2O(g) CO2(g) H2(g)

ΔH / kJ mol−1 −110 −242 −394 0

The standard enthalpy change for this reaction of carbon monoxide and steam is

A +42 kJ mol−1

B −42 kJ mol−1

C +262 kJ mol−1

D −262 kJ mol−1

(Total 1 mark)

Q21. (a) Define the term standard enthalpy of combustion, ∆Hc&ohbar;

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Use the mean bond enthalpy data from the table and the equation given below to calculate a value for the standard enthalpy of combustion of propene. All substances are in the gaseous state.

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Bond C == C C—C C—H O == O O == C O—H

Mean bond enthalpy/ kJ mol–1 612 348 412 496 743 463

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) State why the standard enthalpy of formation, ∆Hfο, of oxygen is zero.

___________________________________________________________________ (1)

(d) Use the data from the table below to calculate a more accurate value for the standard enthalpy of combustion of propene.

Compound C3H6(g) CO2(g) H2O(g)

Standard enthalpy of formation, ∆Hf ο/ kJ mol–1 +20 –394 –242

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(e) Explain why your answer to part (b) is a less accurate value than your answer to part (d).

___________________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q22.

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(a) Explain the meaning of the terms mean bond enthalpy and standard enthalpy of formation.

Mean bond enthalpy __________________________________________________

___________________________________________________________________

___________________________________________________________________

Standard enthalpy of formation __________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (5)

(b) Some mean bond enthalpies are given below.

Bond N–H N–N N≡N H–O O–O

Mean bond enthalpy/kJ mol–1 388 163 944 463 146

Use these data to calculate the enthalpy change for the following gas-phase reaction between hydrazine, N2H4, and hydrogen peroxide, H2O2

+ 2 H––O––O––H N ≡ N + 4 H––O––H

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) Some standard enthalpies of formation are given below.

N2H4(g) H2O2(g) H2O(g)

∆Hfο /kJ mol–1 +75 –133 –242

These data can be used to calculate the enthalpy change for the reaction in part (b).

N2H4(g) + 2H2O2(g) → N2(g) + 4H2O(g)

(i) State the value of ∆HfO for N2(g).

______________________________________________________________

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(ii) Use the ∆HfO values from the table to calculate the enthalpy change for this reaction.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (4)

(d) Explain why the value obtained in part (b) is different from that obtained in part (c)(ii).

___________________________________________________________________

___________________________________________________________________ (1)

(Total 13 marks)

Q23. When 0.10 g of propane was burned the quantity of heat evolved was 5.0 kJ. The enthalpy of combustion of propane in kJ mol−1 is

A −800

B −1500

C −2200


Q24. (a) Iron is extracted from iron(III) oxide using carbon at a high temperature.

(i) State the type of reaction that iron(III) oxide undergoes in this extraction.

______________________________________________________________ (1)

(ii) Write a half-equation for the reaction of the iron(III) ions in this extraction.

______________________________________________________________ (1)

(b) At a high temperature, carbon undergoes combustion when it reacts with oxygen.

(i) Suggest why it is not possible to measure the enthalpy change directly for the following combustion reaction.

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C(s,graphite) + O2(g) CO(g)

______________________________________________________________

______________________________________________________________ (1)

(ii) State Hess's Law.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(iii) State the meaning of the term standard enthalpy of combustion.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(c) Use the standard enthalpies of formation in the table below and the equation to calculate a value for the standard enthalpy change for the extraction of iron using carbon monoxide.

Fe2O3(s) CO(g) Fe(l) CO2(g)

∆Hf/ kJ mol-1 - 822 - 111 +14 - 394

Fe2O3(s) + 3CO(g) 2Fe(I) + 3CO2(g)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(d) (i) Write an equation for the reaction that represents the standard enthalpy of formation of carbon dioxide.

______________________________________________________________ (1)

(ii) State why the value quoted in part (c) for the standard enthalpy of formation of CO2(g) is the same as the value for the standard enthalpy of combustion of carbon.

______________________________________________________________

______________________________________________________________ (1)

(Total 12 marks)

Q25. The table below shows data for the four hydrocarbons ethyne, propyne, propene and propane. ΔHc is the standard enthalpy of combustion of these hydrocarbons.

Compound Name Mr −ΔHc / kJ mol−1

HC≡CH ethyne 26 1300

HC≡CCH3 propyne 40 1940

H2C=CHCH3 propene 42 2060

CH3CH2CH3 propane 44 2220

The complete combustion of 2.0 g of one of the above hydrocarbons releases exactly 100 kJ of heat energy.

This hydrocarbon is

A ethyne

B propyne

C propene

D propane (Total 1 mark)

Q26. A group of students devised an experiment which they believed would enable them to investigate the strength of the intermolecular forces between ethyl ethanoate molecules

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(CH3COOCH2CH3) and trichloromethane molecules (CHCl3).

They mixed exactly 0.10 mol of each of the two liquids in a copper calorimeter and recorded the following results. The starting temperature of both liquids was the same.

Mass of 0.10 mol of ethyl ethanoate / g 8.80

Mass of 0.10 mol of trichloromethane / g 11.95

Increase in temperature (∆T) on mixing / K 9.5

(a) (i) Write an expression for the heat change (q) which relates mass (m), specific heat capacity (c) and change in temperature (∆T).

______________________________________________________________ (1)

(ii) Calculate the amount of heat required to increase the temperature of 8.80 g of ethyl ethanoate by 9.5 K during the mixing process. (You should assume that c for ethyl ethanoate = 1.92 J g–1 K–1)

______________________________________________________________ (1)

(iii) Calculate the amount of heat required to increase the temperature of 11.95 g of trichloromethane by 9.5 K during the mixing process. (You should assume that c for trichloromethane = 0.96 J g–1 K–1)

______________________________________________________________ (1)

(iv) Using the values from parts (a) (ii) and (a) (iii), calculate the molar enthalpy change in kJ mol–1 for the mixing process.

______________________________________________________________

______________________________________________________________ (2)

(b) The students deduced that the heat change was due only to the formation of intermolecular forces between ethyl ethanoate molecules and trichloromethane molecules.

Ignoring all experimental errors, give one reason why the students may have made an incorrect deduction.

___________________________________________________________________

___________________________________________________________________ (1)

(Total 6 marks)

Q27. The sketch graph below shows how the entropy of a sample of water varies with temperature.

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(a) Suggest why the entropy of water is zero at 0 K.

___________________________________________________________________ (1)

(b) What change of state occurs at temperature T1?

___________________________________________________________________ (1)

(c) Explain why the entropy change, ∆S, at temperature T2 is much larger than that at temperature T1.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) It requires 3.49 kJ of heat energy to convert 1.53 g of liquid water into steam at 373 K and 100 kPa.

(i) Use these data to calculate the enthalpy change, ∆H, when 1.00 mol of liquid water forms 1.00 mol of steam at 373 K and 100 kPa.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(ii) Write an expression showing the relationship between free-energy change, ∆G, enthalpy change, ∆H, and entropy change, ∆S.

______________________________________________________________

(iii) For the conversion of liquid water into steam at 373 K and 100 kPa, ∆G = 0 kJ mol–1

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Calculate the value of ∆S for the conversion of one mole of water into steam under these conditions. State the units.

(If you have been unable to complete part (d)(i) you should assume that ∆H = 45.0 kJ mol–1. This is not the correct answer.)

Calculation _____________________________________________________

______________________________________________________________

______________________________________________________________

Units _________________________________________________________ (6)

(Total 10 marks)

Q28. The combustion of hydrocarbons is an important source of energy.

(a) Define the term standard enthalpy of combustion.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) (i) Write an equation for the complete combustion of ethane, C2H6.

______________________________________________________________

(ii) Use the standard enthalpies of formation given below to calculate the standard enthalpy of combustion of ethane.

Formula and state of compound C2H6(g) CO2(g) H2O(l)

Standard enthalpy of formation (at 298 K)/kJ mol–1 –85 –394 –286

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (4)

(c) A container and its contents of total heat capacity 120 J K–1 were heated using a methane burner. Calculate the maximum theoretical temperature rise when 0.10 g of methane was completely burned. The standard enthalpy of combustion of methane is –890 kJ mol–1.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (4)

(Total 11 marks)

Q29. A method of synthesising ammonia directly from nitrogen and hydrogen was developed by Fritz Haber. On an industrial scale, this synthesis requires a high temperature, a high pressure and a catalyst and is very expensive to operate.

(a) Use the data given below to calculate a value for the enthalpy of formation of ammonia

Bond N ≡N H – H N – H

Mean bond enthalpy/kJ mol–1 945 436 391

(3)

(b) A manager in charge of ammonia production wished to increase the daily production of ammonia and reduce the production costs. How would a chemist explain the factors that would influence the commercial efficiency of this production process?


Q30. Hydrogen gas is used in the chemical industry.

(a) Tungsten is extracted by passing hydrogen over heated tungsten oxide (WO3).

(i) State the role of the hydrogen in this reaction.

______________________________________________________________ (1)

(ii) Write an equation for this reaction.

______________________________________________________________ (1)

(iii) State one risk of using hydrogen gas in metal extractions.

______________________________________________________________

______________________________________________________________ (1)

(b) Hydrogen is used to convert oleic acid into stearic acid as shown by the following equation.

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+ H2 CH3(CH2)16COOH

oleic acid stearic acid

(i) Use your knowledge of the chemistry of alkenes to deduce the type of reaction that has occurred in this conversion.

______________________________________________________________ (1)

(ii) State the type of stereoisomerism shown by oleic acid.

______________________________________________________________ (1)

(c) Hydrogen reacts with nitrogen in the Haber Process. The equation for the equilibrium that is established is shown below.

N2(g) + 3H2(g) 2NH3(g)

(i) State Le Chatelier’s principle.

______________________________________________________________

______________________________________________________________ (1)

(ii) Use Le Chatelier’s principle to explain why an increase in the total pressure of this equilibrium results in an increase in the equilibrium yield of ammonia.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(d) Hydrogen reacts with oxygen in an exothermic reaction as shown by the following equation.

H2(g) + O2(g) → H2O(g) ∆H = –242 kJ mol–1

Use the information in the equation and the data in the following table to calculate a value for the bond enthalpy of the H–H bond.

O–H O=O

Mean bond enthalpy / kJ mol–1 + 463 + 496

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 11 marks)

Q31. Barium can be extracted from barium oxide (BaO) in a process using aluminium. A mixture of powdered barium oxide and powdered aluminium is heated strongly. The equation for this extraction process is shown below.

3BaO(s) + 2Al(s) → 3Ba(s) + Al2O3(s)

Some standard enthalpies of formation are given in the table below.

Substance BaO(s) Al2O3(s)

∆Hf&ohbar;/kJ mol–1 –558 –1669

(a) (i) State what is meant by the term standard enthalpy of formation.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) State why the standard enthalpy of formation of barium and that of aluminium are both zero.

______________________________________________________________ (1)

(iii) Use the data to calculate the standard enthalpy change for the reaction shown by the equation above.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

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(b) (i) Suggest the major reason why this method of extracting barium is expensive.

______________________________________________________________ (1)

(ii) Using barium oxide and aluminium powders increases the surface area of the reactants. Suggest one reason why this increases the rate of reaction.

______________________________________________________________ (1)

(c) (i) Write an equation for the reaction of barium with water.

______________________________________________________________ (1)

(ii) A solution containing barium ions can be used to test for the presence of sulfate ions in an aqueous solution of sodium sulfate.

Write the simplest ionic equation for the reaction which occurs and state what is observed.

Simplest ionic equation

______________________________________________________________

Observation ____________________________________________________ (2)

(iii) State how barium sulfate can be used in medicine. Explain why this use is possible, given that solutions containing barium ions are poisonous.

Use __________________________________________________________

Explanation ____________________________________________________

______________________________________________________________ (2)

(Total 14 marks)

Q32. This question is about the extraction of titanium from titanium(IV) oxide by a two-stage process. The first stage in the process produces titanium(IV) chloride. In the second stage, titanium(IV) chloride is converted into titanium. The enthalpy change for the second stage can be determined using Hess’s Law.

(a) Give one reason why titanium is not extracted directly from titanium(IV) oxide using carbon.

___________________________________________________________________

___________________________________________________________________ (1)

(b) Give the meaning of the term enthalpy change.

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(c) State Hess’s Law.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(d) Define the term standard enthalpy of formation.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(e) The following standard enthalpy of formation data refer to the second stage in the extraction of titanium.

TiCl4(g) Na(I) NaCl(s) Ti(s)

ΔHfο/ kJ mol–1 –720 +3 –411 0

(i) State why the value for the standard enthalpy of formation of Na(I) is not zero.

______________________________________________________________

______________________________________________________________ (1)

(ii) Use data from the table to calculate a value for the standard enthalpy change of the following reaction.

TiCl4(g) + 4Na(I) 4NaCl(s) + Ti(s)

______________________________________________________________

______________________________________________________________

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______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(iii) State the role of sodium in this reaction.

______________________________________________________________ (1)

(Total 11 marks)

Q33. A scientist used mass spectrometry to analyse a sample of the air near a fertiliser factory. The sample of air included traces of a gas which was shown by its molecular ion to have a precise Mr = 44.00105

(a) State the meaning of the term molecular ion.

___________________________________________________________________

___________________________________________________________________ (1)

(b) (i) Use the following data to show that the trace gas was dinitrogen oxide (N2O).

Show your working.

Atom Precise relative atomic mass

12C 12.00000

14N 14.00307

16O 15.99491

______________________________________________________________

______________________________________________________________ (1)

(ii) Propane is used as a fuel in the fertiliser factory. State why both propane and its combustion product, carbon dioxide, might have been identified as the trace gas if the scientist had used relative molecular masses calculated to one decimal place.

of 56

______________________________________________________________

______________________________________________________________ (1)

(iii) State why the precise relative atomic mass for the 12C isotope is exactly 12.00000

______________________________________________________________ (1)

(c) Dinitrogen oxide is formed when ammonia is oxidised according to the following equation.

2NH3(g) + 2O2(g) → N2O(g) + 3H2O(l)

(i) Use the standard enthalpies of formation in the table below to calculate a value for the standard enthalpy change of this reaction.

NH3(g) O2(g) N2O(g) H2O(l)

ΔHfο/ kJ mol–1 –46 0 +82 –286

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) State one condition necessary for enthalpies of formation to be quoted as standard values at a specified temperature of 298 K.

______________________________________________________________ (1)

(Total 8 marks)

Q34. Comparison of lattice enthalpies from Born-Haber cycles with lattice enthalpies from calculations based on a perfect ionic model are used to provide information about bonding in crystals.

(a) Define the terms enthalpy of atomisation and lattice dissociation enthalpy.

Enthalpy of atomisation ________________________________________________

___________________________________________________________________

___________________________________________________________________

Lattice dissociation enthalpy ____________________________________________

___________________________________________________________________

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___________________________________________________________________ (4)

(b) Use the following data to calculate a value for the lattice dissociation enthalpy of sodium chloride.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) Consider the following lattice dissociation enthalpy (ΔHLο) data.

NaBr AgBr

ΔHLο(experimental)/kJ mol–1 +733 +890

ΔHLο(theoretical)/kJ mol–1 +732 +758

The values of ΔHLο (experimental) have been determined from Born–Haber cycles.

The values of ΔHLο (theoretical) have been determined by calculation using a perfect ionic model.

(i) Explain the meaning of the term perfect ionic model.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) State what you can deduce about the bonding in NaBr from the data in the table.

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______________________________________________________________

______________________________________________________________ (1)

(iii) State what you can deduce about the bonding in AgBr from the data in the table.

______________________________________________________________

______________________________________________________________ (1)

(Total 11 marks)

Q35. Ammonia can be manufactured by the Haber Process.

The equation for the reaction that occurs is shown below.

N2(g) + 3H2(g) 2NH3(g)

(a) The table below contains some bond enthalpy data.

N N H–H N–H

Mean bond enthalpy / kJ mol–1 944 436 388

(i) Use data from the table to calculate a value for the enthalpy of formation for one mole of ammonia.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) A more accurate value for the enthalpy of formation of ammonia is –46 kJ mol–1. Suggest why your answer to part (a) (i) is different from this value.

______________________________________________________________

______________________________________________________________ (1)

(b) The table below contains some entropy data.

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H2(g) N2(g) NH3(g)

Sο / J K–1 mol–1 131 192 193

Use these data to calculate a value for the entropy change, with units, for the formation of one mole of ammonia from its elements.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) The synthesis of ammonia is usually carried out at about 800 K.

(i) Use the ΔH value of –46 kJ mol–1 and your answer from part (b) to calculate a value for ΔG, with units, for the synthesis at this temperature. (If you have been unable to obtain an answer to part (b), you may assume that the entropy change is –112 J K–1 mol –1. This is not the correct answer.)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Use the value of ΔG that you have obtained to comment on the feasibility of the reaction at 800 K.

______________________________________________________________ (1)

(Total 11 marks)

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Mark schemes

Q1. (a) Enthalpy change when 1 mol of compound (1)

Is formed from it’s elements (1)

All substances in their standard state (1) 3

(b) ΔH = ΣΔHοc (reactants) – ΣΔHοc (products) (1)

= (7x – 394) + (4 x – 286) – (– 3909) (1)

= + 7 kJmol–1 (1) 3

(c) Heat change = m c ΔT (1)

= 250 × 4.18 × 60 = 62700J = 62.7kJ (1)

Moles C7H8 = 2.5 /92 = 0.0272 (1)

ΔH = 62.7 / 0.0272 = – 2307 kJ mol–1 (1) (allow –2300 to –2323)

4

(d) Mass of water heated = 25 + 50 = 75g Temp rise = 26.5 – 18 = 8.5 °C

both for (1) mark

Heat change = 75 × 4.18 × 8.5 = 2665 J = 2.665 kJ (1)

Moles HCl = 0.05 (1)

ΔH = – 2.665 / 0.05 = –53.3 kJmol–1 (1) (allow –53 to –54)

4

(e) Less heat loss (1) 1

[15]

Q2. C

[1]

Q3. (a) (Energy required) to break a given covalent bond (1)

averaged over a range of compounds (1) Penalise first mark if ‘energy’ / ‘enthalpy’ evolved

2

(b) (i) 4 × C−H = 4 × 413 = +1652

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1 × C−C = 1 × 347 = 347 1 × C=O = 1 × 736 = 736 2½ × O=O = 2.5 × 498 = 1245 (1) = 2735 + 1245 = +3980 (1)

first mark for 4 : 1: 1 or 2735 ignore sign

(ii) 4 × H−O = -4 × 464 = –1856 4 × C−O = -4 × 736 = –2944 (1) = –4800 (1)

First mark for 4 : 4

(iii) ΔHR = ΣBonds broken − ΣBonds made = +3980 − 4800 = −820 (1)

Conseq Mark for incorrect answers in (i) and (ii) as (i) Answer + (ii) Answer =

5 [7]

Q4. (a) 2AgNO3 + Zn → Zn(NO3)2 + 2Ag (1)

Accept an ionic equation i.e.2Ag+ +Zn → 2Ag + Zn2+

1

(b) Moles = mv / 1000 (1) = 0.20 × 50/1000 = 1.00 × 10–2

2

(c) Heat energy change = mCΔT (1) = 50 × 418 × 3.2 J

= 669 J (Ignore signs) (1) Allow 668, 67.0 0.67kJ Penalise wrong units if given

2

(d) = 134 kJ mol–1

Mark one : 2 × (answer to (c)) Mark two : Dividing by answers to (b) Allow 133 – 134 Penalise incorrect units Mark conseq to equation in (a) for full marks, also to that in (c) If No working is shown and answer is incorrect zero

2

(e) Incomplete reaction or Heat loss (1) 1

[8]

Q5. (a) (Enthalpy change) when 1 mol (1) of a compound is formed

from its constituent elements (1) in their standard states (1) 3

Allow energy or heat, Ignore evolved or absorbed Mark each point independently

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(b) (The enthalpy change for a reaction is) independent of the route (1) 1

(c) ΔHR = Hf products ‑ Hf reactants (1) = [(3 × -286) + (3 × -394)] ‑ (-248) (1) = -1792 (1) (kJ mol–1)

Deduct one mark for each error to zero 3

[7]

Q6. (a) Heat energy change (1)

Not energy on its own

measured at constant pressure (1) Mark separately, ignore constant temperature statements

2

(b) (i) Enthalpy change when 1 mol of a substance (or compound / product) (1) is formed from its constituent elements (1) in their standard states (1) under standard conditions (1)

Mark separately

(ii) 2Na(s) + S(s) + 2O2(g) → Na2SO4(s) Balanced (1) State symbols (1), but only if all species are correct

Allow S8 (s) 5

(c) Enthalpy change is independent of reaction route (1) Penalise incorrect additional statements

1

(d)

–1356 + (2 × 285.8) + (4 × 393.5) + ΔHfC4H4O4 = 0

ΔHf = –789.6 kJ mol–1

If answer is incorrect: Score +789.6 two marks Score (× 1); (× 2) and (× 4) for species - one mark If an incorrect negative answer given check for AE for loss of

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one mark 3

[11]

Q7. A

[1]

Q8. (a) Enthalpy (Energy) to break a (covalent) bond (1) OR dissociation energy

Varies between compounds so average value used (1) QL mark OR average of dissociation energies in a single molecule / e.g. CH4

Do not allow mention of energy to form bonds but with this case can allow second mark otherwise 2nd mark consequential on first

2

(b) (i) 1/2 N2 + 3/2 H2 → NH3 (1) Ignore s s

(ii) ΔH = (Σ)bonds broken – (Σ)bonds formed (1) = 1/2 × 944 + 3/2 × 436 – 3 × 388 (1) = –38 kJ mol–1 (1)

Ignore no units, penalise wrong units Score 2/3 for -76 1/3 for +38 Allow 1/3 for +76

4

(c) 4 (C–H) + (C=C) + (H–H) – (6 (C–H) + (C–C)) = –136 (1) OR (C=C) + (H–H) – ((C–C) + 2 (C–H)) = –136 2 (C–H) = 836 (1) (C–H) = 418 (kJ mol–1) (1)

Note: allow (1) for –836 another (1) for –418

3 [9]

Q9. C

[1]

Q10. (a) C3H6O + 4O2 → 3CO2 + 3H2O (1) (or multiple) 1

(b) (i) (1) = 0.0250 (1) allow 0.025

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allow conseq on wrong Mr

1.45/100, CE; C.E.

(ii) heat released = mcΔT = 100 × 4.18 × 58.1 (1)

if 1.45 used in place of 100 CE = 0

= 24300 J (1) (or 24.3kJ) allow 24200 to 24300 ignore decimal places units tied to answer If use 0.1 × 4.18 × 51.8 allow ½ for 24.3 with no units

(iii) = –972 (kJ mol–1) (1) allow –968 to –973 allow +972 allow conseq allow no units penalise wrong units

5

(c) (i) Heat loss (1) or energy loss do not allow incomplete combustion

(ii) Difference: more negative (1) (or more exothermic) QoL mark

Explanation: heat (or energy) released when water vapour condenses (1) or heat/energy required to vaporise water or water molecules have more energy in the gaseous state

3

(d) ΔH = ΣΔHreactants – ΣΔHproducts (1)

(or cycle ) = (2 × –394) + (3 × –286) + (–297) – (–1170) (1) = –773 (1)

ignore units even if wrong Allow 1/3 for +773

3 [12]

Q11. (a) (i) enthalpy (or heat or heat energy) change when

1 mol of a substance (1) (QL mark) is formed from its elements (1)

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all substances in their standard states (1) (or normal states at 298K, 100 kPa or std condits)

not STP, NTP 3

(b) enthalpy change (or enthalpy of reaction) is independent of route (1)

ΔH = ΣΔHf prods - ΣΔHf reactants (or cycle) (1) minimum correct cycle is:

ΔH = -642 – 286 – (–602 + 2 × –92) (1) = –142 (kJ mol–1) (1)

penalise this mark for wrong units +142 scores 1 mark out of the last three

4

(c) ΔH = mcT (1) (or mcΔT) = 50 × 4.2 × 32 = 6720 J = 6.72J (1)

mark is for 6720 J or 6.72 kJ

moles HCl = × conc = × 3 (1)

= 0.15 (1) if error here mark on conseq.

Therefore moles of MgO reacted = moles HCl/2 (1) (mark is for/2, CE if not/2) = 0.15/2 = 0.075

Therefore ΔH = 6.72/0.075 (1) = –90 kJ (mol–1)

kJ must be given, allow 89 to 91 value (1) sign (1); this mark can be given despite CE for /2

8

Note various combinations of answers to part (c) score as follows:

–89 to –91 kJ (8) (or –89000 to 91000J) no units (7)

+89 to +91 kJ (7) (or + 89000 to +91000J) no units (6)

–44 to –46 kJ (5) (or -44000 to -46000J) no units (4) if units after 6.72 or 6720 (5)

+44 to +46 kJ (4) (or +44000 to + 46000) if no units and

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if no units after 6.72 or 6720 (3) otherwise check, could be (4)

[15]

Q12. C

[1]

Q13. A

[1]

Q14. D

[1]

Q15. D

[1]

Q16. D

[1]

Q17. A

[1]

Q18. (a) ΔH = Σ(bonds broken) – Σ(bonds formed) (or cycle)

1

= +146 – 496/2 (or 2 × 463 + 146 –(2 × 463 + 496/2) 1

= – 102 (kJ mol–1) (1) (accept no units, wrong units loses a mark; +102 scores (1) only)

1

(b) C(s) + 2H2(g) → CH4(g) equation (1) Correct state symbols (1) 2

(c) (i) Macromolecular (accept giant molecule or carbon has many (4) bonds)

1

(ii) ΔH = ΣΔHf(products) – ΣΔHf (reactants) (or cycle) 1

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= 715 + 4 × 218 – (–74.9) 1

= 1662 (kJ mol–1) (accept no units, wrong units loses one mark, allow 1660 to 1663, –1662 scores one mark only)

1

(iii) 1662/4 = 415.5 (mark is for divide by four, allow if answer to (c)(ii) is wrong)

1 [10]

Q19. B

[1]

Q20. B

[1]

Q21. (a) enthalpy change/ heat energy change when 1 mol of a substance

1

is completely burned in oxygen 1

at 298K and 100 kPa or standard conditions 1

(not 1atm)

(b) ∆H = ∑ bonds broken – ∑ bonds formed 1

= (6 × 412) + 612 +348 + (4.5 × 496) – ((6 × 743) + (6 × 463)) 1

= – 1572 kJ mol–1

1

(c) by definition ∆Hf is formation from an element 1

(d) ∆Hc = ∑ ∆Hf products -∑ ∆Hf reactants or cycle 1

= (3 × – 394) + (3 × –242) – (+20) 1

= − 1928 kJ mol–1

1

(e) bond enthalpies are mean/average values 1

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from a range of compounds 1

[12]

Q22. (a) enthalpy (or energy) to break (or dissociate) a bond;

1

averaged over different molecules (environments); 1

enthalpy (or heat energy) change when one mole of a compound; 1

is formed from its elements; 1

in their standard states; 1

(b) enthalpy change = Σ(bonds broken) – Σ(bonds formed) or cycle; 1

= 4 × 388 +163 + 2 × 146 + 4 × 463 – (944 + 8 × 463); (or similar)

1

= –789; (+ 789 scores 1 only)

1

(c) (i) zero; 1

(ii) AH = Σ (enthalpies of formation of products) –Σ (enthalpies of formation of reactants)

1

= 4 × –242-(75 + 2 × –133); 1

= –777; (+ 777 scores one only)

1

(d) mean bond enthalpies are not exact (or indication that actual values are different from real values)

1 [13]

Q23. C

[1]

Q24. (a) (i) reduction OR reduced OR redox OR reduction–oxidation

of 56

Not “oxidation” alone 1

(ii) Fe3+ + 3e–

Fe

Ignore state symbols Do not penalise absence of charge on electron Credit Fe3+ Fe – 3e–

Credit multiples 1

(b) (i) Because (one of the following)

CO is not the only product OR Reference to “incomplete combustion to form CO” does not answer the question

(Some) complete combustion (also)occurs OR

CO2 is (also) formed

Further oxidation occurs 1

(ii) The enthalpy change / heat (energy) change at constant pressure in a reaction is independent of the route / path taken (and depends only on the initial and final states)

1

(iii) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / element For M1, credit correct reference to molecule/s or atom/s

M2 is burned completely / undergoes complete combustion in (excess) oxygen

M3 with all reactants and products / all substances in standard states For M3 Ignore reference to 1 atmosphere

OR all reactants and products / all substances in normal / specified states under standard conditions / 100 kPa / 1 bar and specified T / 298 K

3

(c) M1 (could be scored by a correct mathematical expression which must have all ∆H symbols and the ∑)

Correct answer gains full marks Credit 1 mark ONLY for –1 (kJ mol–1)

M1 ∆Hr = ∑∆Hf (products) – ∑∆Hf (reactants) Credit 1 mark ONLY for – 27 (kJ mol–1) i.e. assuming value for Fe(l) = 0

OR correct cycle of balanced equations with 2Fe, 3C and 3O2

M2 ∆Hr = 2(+14) + 3(– 394) – (– 822) – 3(–111)

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= 28 –1182 + 822 + 333


M3 = (+) 1 (kJ mol–1)

(Award 1 mark ONLY for – 1)

(Award 1 mark ONLY for – 27) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a

transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2)

• If no AE, check for a correct method; this requires either a correct cycle with 2Fe, 3C and 3O2 OR a clear statement of M1 which could be in words and scores only M1

3

(d) (i) C(s) + O2(g) CO2(g) State symbols essential Possible to include C(s, graphite)

1

(ii) These two enthalpy changes are for the same reaction / same equation / same reactants and products

Penalise reference to CO2 being produced by a different route

OR

They both make one mole of carbon dioxide only from carbon and oxygen (or this idea clearly implied)

“both form CO2” is not sufficient (since other products might occur e.g.CO)

OR

The same number and same type of bonds are broken and formed 1

[12]

Q25. A

[1]

Q26. (a) (i) q = mc ΔT

Ignore case except T 1

(ii) 8.80 × 1.92 × 9.5 = 161 (J) to 160.5(12) (J) Credit 0.161 provided it is clear that it is kJ. Penalise wrong units

1

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(iii) 11.95 × 0.96 × 9.5 = 109 (J) to 108.98(4) (J) Credit 0.109 provided it is clear that it is kJ. Penalise wrong units.

1

(iv) M1 Addition of (a)(ii) and (a)(iii)

M2 Multiply by 10 and convert to kJ (divide by 1000) leading to an answer Consequential on (a)(ii) and (a)(iii) Penalise wrong units Ignore the sign

Therefore ΔH = (–) 2.69 OR (–) 2.7(0) (kJ mol–1) Ignore greater numbers of significant figures (2.69496) Subtraction in M1 is CE

2

(b) One from:

• No account has been taken of the intermolecular forces initially in the two liquids OR each liquid has its own intermolecular forces in operation before mixing.

• The liquids may react or reference to reaction or reference to bonds broken or formed

Any statement which shows that there are other intermolecular forces to consider. Ignore heat loss and ignore poor mixing.

1 [6]

Q27. (a) Particles are in maximum state of order

(or perfect order or completely ordered or perfect crystal or minimum disorder or no disorder) (entropy is zero at 0 k by definition)

1

(b) (Ice) melts (or freezes or changes from solid to liquid or from liquid to solid)

1

(c) Increase in disorder 1

Bigger (at T2) 1

Second mark only given if first mark has been awarded

(d) (i) Moles of water = 1.53/18 (= 0.085) 1

Heat change per mole = 3.49/0.085 = 41.1 (kJ mol–1) (allow 41 to 41.1, two sig. figs.) (penalise –41 (negative value), also penalise wrong units but

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allow kJ only) 1

(ii) ΔG = ΔH – TΔS 1

(iii) ΔH = TΔS or ΔS = ΔH/T (penalise if contradiction)

1

ΔS = 41.1/373 = 0.110 kJ K–1 (mol–1) (or 110 (J K–1 (mol–1)) (allow 2 sig. figs.) (if use value given of 45, answer is 0.12 (or 120 to 121) (if ΔH is negative in (d) (i), allow negative answer) (if ΔH is negative in (d) (i), allow positive answer) (if ΔH is positive in (d) (i), penalise negative answer)

1

Correct units as above (mol–1 not essential) 1

[10]

Q28. (a) The enthalpy change when 1 mol of a compound

1

is completely burnt in oxygen 1

under standard conditions, or 298K and 100kPA 1

(b) (i) C2H6 + 3½O2 → 2CO2 + 3H2O 1

(ii) ΔH = 2 × ΔHfο (CO2) + 3 × ΔHfο (H2O) – ΔHfο (C2H6) 1

= – 788 – 858 – (–85) 1

= – 1561 kJ mol–1

1

(c) moles methane = = 6.25 × 10–3

1 kJ evolved = 6.25 × 10–3 × 890 = 5.56

1 5.56 × 103 joules = (mc)ΔT

1

ΔT = = 46.4 K 1

[11]

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Q29. (a) Equation 1/2N2 + 3/2H2 → NH3

1

ΔHf = [(945 × 0.5) + (426 × 1.5)] – (391 × 3) 1

= –46.5 kJ mol–1

1

Mark Range

The marking scheme for this part of the question includes an overall assessment for the Quality of Written Communication (QWC). There are no discrete marks for the assessment of QWC but the candidates’ QWC in this answer will be one of the criteria used to assign a level and award the marks for this part of the question

Descriptor an answer will be expected to meet most of the criteria in the level

descriptor

4-5 – claims supported by an appropriate range of evidence

– good use of information or ideas about chemistry, going beyond those given in the question

– argument well structured with minimal repetition or irrelevant points

– accurate and clear expression of ideas with only minor errors of grammar, punctuation and spelling

2-3 – claims partially supported by evidence

– good use of information or ideas about chemistry given in the question but limited beyond this

– the argument shows some attempt at structure

– the ideas are expressed with reasonable clarity but with a few errors of grammar, punctuation and spelling

0-1 – valid points but not clearly linked to an argument structure

– limited use of information or ideas about chemistry

– unstructured

– errors in spelling, punctuation and grammar or lack of fluency

(b) The higher the temperature the faster the reaction QWC 1

but, since the reaction is exothermic 1

the equilibrium yield is lower QWC 1

The higher the pressure the greater the equilibrium yield QWC 1

because there is a reduction in the number of moles of gas in the reaction

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1

but higher pressure is expensive to produce or plant is more expensive to build QWC

1

A better catalyst would lessen the time to reach equilibrium 1

and allow more ammonia to be produced in a given time QWC 1

[11]

Q30. (a) (i) Reducing agent

OR

Reduce(s) (WO3/tungsten oxide)

OR

electron donor

OR

to remove oxygen (from WO3/tungsten oxide or to form water); 1

(ii) WO3 + 3H2 → W + 3H2O Or multiples

1

(iii) One from

H2 is

• explosive

• flammable or inflammable

• easily ignited Ignore reference to pressure or temperature

1

(b) (i) Addition Ignore “electrophilic” Penalise “nucleophilic addition”

OR

(catalytic) hydrogenation

OR

Reduction 1

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(ii) Geometric(al)

OR

cis/trans OR E Z OR E/Z 1

(c) (i) (If any factor is changed which affects an equilibrium), the position of equilibrium will shift/move/change/respond/act so as to oppose the change.

OR

(When a system/reaction in equilibrium is disturbed), the equilibrium shifts/moves in a direction which tends to reduce the disturbance

A variety of wording will be seen here and the key part is the last phrase and must refer to movement of the equilibrium. QoL

1

(ii) M1 – Statement of number of moles/molecules There are more moles/molecules (of gas) on the left/of reactants

OR

fewer moles/molecules (of gas) on the right./products

OR

there are 4 moles/molecules (of gas) on the left and 2 moles/ molecules on the right.

Ignore “volumes” for M1 Mark independently

M2 – Explanation of response/movement in terms of pressure Increase in pressure is opposed (or words to that effect)

OR

pressure is lowered by a shift in the equilibrium (from left) to right/favours forward reaction.

2

(d) ΣB(reactants) – ΣB(products) = ΔH (M1)

OR

Sum of bonds broken – Sum of bonds formed = ΔH (M1)

B(H–H) + ½B(O=O) – 2B(O–H) = – 242 (M1)

B(H–H) = – 242 – ½(+496) + 2(+463) (this scores M1 and M2)

B(H–H) = (+)436 (kJ mol–1) (M3)

Award 1 mark for – 436

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Candidates may use a cycle and gain full marks. M1 could stand alone Award full marks for correct answer. Ignore units. Two marks can score with an arithmetic error in the working.

3 [11]

Q31. (a) (i) M1 The enthalpy change / heat change at constant pressure

when 1 mol of a compound / substance / product 1

M2 Is formed from its (constituent) elements 1

M3 With all reactants and products / all substances in standard states OR All reactants and products / all substances in normal states under standard conditions / 100 kPa / 1 bar and specified T / 298 K

Ignore reference to 1 atmosphere 1

(ii) By definition OR Because they are elements

1

(iii) M1 ΔHf = ΣΔHf (products) – ΣΔHf(reactants) 1

M2 = –1669 – 3(–558) (This also scores M1)

1

M3 = (+) 5 (kJ mol–1) Correct answer gains full marks. Assume the value is positive unless specifically stated as negative. Credit 1 mark if – 5 (kJ mol–1). For other incorrect or incomplete answers, proceed as follows: • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 3BaO OR a clear statement of M1 which could be in words and scores only M1

1

(b) (i) One from

• Aluminium is expensive (to extract OR due to electrolysis)

• High energy cost

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• The cost of heating strongly This requires a clear statement about cost

1

(ii) One from

• increase collision frequency

• OR more collisions

• OR more chance of colliding The answer MUST refer to more collisions. Ignore “more available to collide”

1

(c) (i) Ba + 2H2O → Ba(OH)2 + H2

Ignore state symbols Allow multiples and correct ionic equations

1

(ii) M1 Ba2+ + SO42– → BaSO4

(or the ions together) Allow crossed out Na+ ions, but penalise if not crossed out

1

M2 White precipitate / white solid Ignore state symbols Ignore “milky”

1

(iii) M1 Barium meal or ( internal ) X-ray or to block X-rays 1

M2 BaSO4 / barium sulfate is insoluble (and therefore not toxic) Accept a correct reference to M1 written in the explanation in M2, unless contradictory. For M2 NOT barium ions NOT barium NOT barium meal and NOT “It”. Ignore radio-tracing.

1 [14]

Q32. (a) One from

• Ti is not produced

• TiC / carbide is produced OR titanium reacts with carbon

• Product is brittle

• Product is a poor engineering material Penalise “titanium carbonate” Ignore “impure titanium” Credit “titanium is brittle”

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1

(b) Heat (energy) change at constant pressure QoL

1

(c) The enthalpy change in a reaction is independent of the route taken (and depends only on the initial and final states)

Credit “heat change at constant pressure” as an alternative to “enthalpy change”

1

(d) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / product

For M1, credit correct reference to molecule/s or atom/s

M2 is formed from its (constituent) elements

M3 with all reactants and products / all substances in standard states

OR all reactants and products / all substances in normal states under standard conditions / 100 kPa / 1 bar and any specified T (usually 298 K)

Ignore reference to 1 atmosphere 3

(e) (i) Na / it is not in its standard state / normal state under standard conditions

OR

Standard state / normal state under standard conditions for Na is solid / (s)

QoL Ignore “sodium is a liquid or sodium is not a solid”

1

(ii) M1 ∆Hr = ∑∆Hf (products) - ∑∆Hf (reactants)

M2 ∆Hr = 4(−411) − (−720) − 4(+3) = −1644 + 720 − 12 (This also scores M1)

M3 = −936 (kJ mol−1) Correct answer gains full marks Credit 1 mark for + 936 (kJ mol−1) Credit 1 mark for – 924 (kJ mol−1) i.e. assuming value for Na(l) = 0 For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either

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a correct cycle with 2Cl2 and 4Na OR a clear complete statement of M1 which could be in words and scores only M1

3

(iii) Reducing agent Ignore “reduces titanium”

OR reductant OR reduces TiCl4

OR electron donor 1

[7]

Q33. (a) The molecular ion is

• The molecule with one/an electron knocked off/lost Ignore the highest or biggest m/z peak

OR

• The molecule with a (single) positive charge

OR

• the ion with/it has the largest/highest/biggest m/z (value/ratio) Ignore “the peak to the right”

OR

• the ion with/it has an m/z equal to the Mr

Ignore “compound” 1

(b) (i) 2(14.00307) + 15.99491 = 44.00105 A sum is needed to show this

1

(ii) Propane/C3H8 and carbon dioxide/CO2 (and N2O) or they or both the gases/molecules or all three gases/molecules have an (imprecise) Mr of 44.0 (OR 44)

OR

they have the same Mr or molecular mass (to one d.p) This could be shown in a calculation of relative masses for propane and carbon dioxide

1

(iii) By definition

OR

The standard/reference (value/isotope) Ignore “element”

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Ignore “atom” 1

(c) (i) M1 (could be scored by a correct mathematical expression)

ΔH = ΣΔHproducts – ΣΔHreactants


M1 and M2 can be scored with correct moles as follows ΔH + 2(– 46) = +82 + 3(– 286)

ΔH – 92 = – 776

ΔH = 92 – 776 OR 92 + 82 – 858

M3 ΔH = – 684 (kJ mol–1) (This is worth 3 marks)

Award 1 mark ONLY for + 684 Full marks for correct answer. Ignore units. Deduct one mark for an arithmetic error.

3

(ii) The value is quoted at a pressure of 100 kPa OR 1 bar or 105 Pa

OR

All reactants and products are in their standard states/their normal states at 100 kPa or 1 bar

Ignore 1 atmosphere/101 kPa Ignore “constant pressure”

1 [8]

Q34. (a) Enthalpy change for the formation of 1 mol of gaseous atoms

allow heat energy change for enthalpy change 1

From the element (in its standard state) ignore reference to conditions

1

Enthalpy change to separate 1 mol of an ionic lattice/solid/compound enthalpy change not required but penalise energy

1

Into (its component) gaseous ions mark all points independently

1

(b) ΔHL = –ΔHf + ΔHa + I.E. + 1/2E(Cl-Cl) + EA Or correct Born-Haber cycle drawn out

1

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= +411 + 109 + 494 + 121 – 364 1

= +771 (kJ mol–1) –771 scores 2/3 +892 scores 1/3 –51 scores 1/3 –892 scores zero +51 scores zero ignore units

1

(c) (i) Ions are perfect spheres (or point charges) 1

Only electrostatic attraction/no covalent interaction mention of molecules/intermolecular forces/covalent bonds CE = 0 allow ionic bonding only If mention of atoms CE = 0 for M2

1

(ii) Ionic Allow no covalent character/bonding

1

(iii) Ionic with additional covalent bonding Or has covalent character/partially covalent Allow mention of polarisation of ions or description of polarisation

1 [11]

Q35. (a) (i) ΔH = Σ bonds broken –Σ bonds formed

1

= 944/2 + 3/2 × 436 –3 × 388 1

= –38 (kJ mol–1) ignore units even if incorrect correct answer scores 3 –76 scores 2/3 +38 scores 1/3

1

(ii) mean / average bond enthalpies are from a range of compounds or mean / average bond enthalpies differ from those in a single compound / ammonia

1

(b) ΔS = ΣS products –Σ S reactants 1

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= 193 – (192/2 + 131 × 3/2) 1

= –99.5 J K–1 mol–1

units essential for M3 correct answer with units scores 3 –199 J K–1 mol–1 & –99.5 score 2/3 –199 and + 99.5 J K–1 mol–1 score 1/3

1

(c) (i) ΔG = ΔH – TΔS = –46 + 800 × 99.5/1000 mark is for putting in numbers with 1000 if factor of 1000 used incorrectly CE = 0

1

= 33.6 or 33600 allow 33 to 34 (or 33000 to 34000)

1

kJ mol–1 with J mol–1

correct units for answer essential if answer to part (b) is wrong or if -112 used, mark consequentially e.g. • –199 gives 113 to 114 kJ mol–1 (scores 3/3) • –112 gives 43 to 44 kJ mol–1 (scores 3/3)

1

(ii) If answer to (c) (i) is positive: not feasible / not spontaneous

If answer to (c) (i) is negative: feasible / spontaneous if no answer to (c) (i) award zero marks

1 [11]

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Equilibrium and Kc exam pack 1

Name: ________________________

Class: ________________________

Date: ________________________

Time: 351 minutes

Marks: 318 marks

Comments:

At Minimum complete:

Q1 – straight forward Kc – 9 marks

Q2. Harder Kc – 10 marks- A/A*

Q3 – equilibrium -12 marks

Q5 – Kc and equilibrium – 10 marks

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Q1. When heated above 100 °C, nitrosyl chloride (NOCl) partly decomposes to form nitrogen monoxide and chlorine as shown in the equation.

2NOCl(g) 2NO(g) + Cl2(g)

(a) A 2.50 mol sample of NOCl was heated in a sealed container and equilibrium was established at a given temperature. The equilibrium mixture formed contained 0.80 mol of NO.

Calculate the amount, in moles, of Cl2 and of NOCl in this equilibrium mixture.

Moles of Cl2 _______________________________________________________

Moles of NOCl _____________________________________________________ (2)

(b) A different mixture of NOCl, NO and Cl2 reached equilibrium in a sealed container of volume 15.0 dm3. The equilibrium mixture formed contained 1.90 mol of NOCl and 0.86 mol of NO at temperature T.

The value of Kc for the equilibrium at temperature T was 7.4 × 10−3 mol dm−3.

(i) Write an expression for the equilibrium constant Kc

______________________________________________________________

______________________________________________________________ (1)

(ii) Calculate the amount, in moles, of Cl2 in this equilibrium mixture.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________

______________________________________________________________ (4)

(iii) Consider this alternative equation for the equilibrium at temperature T.

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NOCl(g) NO(g) + Cl2(g)

Calculate a value for the different equilibrium constant Kc for the equilibrium as shown in this alternative equation. Deduce the units of this Kc

Calculation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Units _________________________________________________________

______________________________________________________________ (2)

(Total 9 marks)

Q2.

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Q3. Ammonia is manufactured by the Haber process in which the following equilibrium is established.

N2(g) + 3H2(g) 2NH3(g)


Feature 1 __________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Feature 2 __________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) Explain why a catalyst has no effect on the position of an equilibrium.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (2)

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(c) The diagram shows how the equilibrium yield of ammonia varies with changes in pressure and temperature.

(i) Use the diagram to state the effect of an increase in pressure at constant temperature on the yield of ammonia. Use Le Chatelier's principle to explain this effect.

Effect on yield __________________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(ii) Use the diagram to state the effect of an increase in temperature at constant pressure on the yield of ammonia. Use Le Chatelier's principle to explain this effect.

Effect on yield __________________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

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______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(d) At equilibrium, with a pressure of 35 MPa and a temperature of 600 K, the yield of ammonia is 65%.

(i) State why industry uses a temperature higher than 600 K.

______________________________________________________________

______________________________________________________________ (1)

(ii) State why industry uses a pressure lower than 35 MPa. Do not include references to safety.

______________________________________________________________

______________________________________________________________ (1)

(Total 12 marks)

Q4. At high temperatures and in the presence of a catalyst, sulfur trioxide decomposes according to the following equation.

2SO3(g)

2SO2(g) + O2(g) ∆Hϴ = +196 kJ mol–1

(a) In an experiment, 8.0mol of sulfur trioxide were placed in a container of volume 12.0 dm3 and allowed to come to equilibrium. At temperature T1 there were 1.4 mol of oxygen in the equilibrium mixture.

(i) Calculate the amount, in moles, of sulfur trioxide and of sulfur dioxide in the equilibrium mixture.

Amount of sulfur trioxide __________________________________________

Amount of sulfur dioxide __________________________________________ (2)

(ii) Write an expression for the equilibrium constant, Kc, for this equilibrium.

______________________________________________________________

______________________________________________________________ (1)

(iii) Deduce the units of Kc for this equilibrium.

______________________________________________________________

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______________________________________________________________ (1)

(iv) Calculate a value of Kc for this equilibrium at temperature T1

(If you were unable to complete the calculations in part (a)(i) you should assume that the amount of sulfur trioxide in the equilibrium mixture was 5.8 mol and the amount of sulfur dioxide was 2.1 mol. These are not the correct values.)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(b) The experiment was repeated at the same temperature using the same amount of sulfur trioxide but in a larger container. State the effect, if any, of this change on:

(i) the amount, in moles, of oxygen in the new equilibrium mixture

______________________________________________________________ (1)

(ii) the value of Kc

______________________________________________________________ (1)

(c) The experiment was repeated in the original container but at temperature T2

The value of Kc was smaller than the value at temperature T1

State which is the higher temperature, T1 or T2


Higher temperature ___________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

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___________________________________________________________________ (3)

(Total 12 marks)

Q5. (a) A mixture of 1.50 mol of hydrogen and 1.20 mol of gaseous iodine was sealed in a

container of volume V dm3. The mixture was left to reach equilibrium as shown by the following equation.

H2(g) + l2(g)

2Hl(g)

At a given temperature, the equilibrium mixture contained 2.06 mol of hydrogen iodide.

(i) Calculate the amounts, in moles, of hydrogen and of iodine in the equilibrium mixture.

Moles of hydrogen ______________________________________________

Moles of iodine _________________________________________________ (2)

(ii) Write an expression for the equilibrium constant (Kc) for this equilibrium.

______________________________________________________________

______________________________________________________________ (1)

(iii) Kc for this equilibrium has no units. State why the units cancel in the expression for Kc

______________________________________________________________

______________________________________________________________ (1)

(iv) A different mixture of hydrogen, iodine and hydrogen iodide was left to reach equilibrium at the same temperature in a container of the same volume. This second equilibrium mixture contained 0.38 mol of hydrogen, 0.19 mol of iodine and 1.94 mol of hydrogen iodide.

Calculate a value for Kc for this equilibrium at this temperature.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________

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(2)

(b) This question concerns changes made to the four equilibria shown in parts (b)(i) to (b)(iv). In each case, use the information in the table to help you choose from the letters A to E the best description of what happens as a result of the change described. Write your answer in the box.

Each letter may be used once, more than once or not at all.

Position of equilibrium Value of equilibrium constant, Kc

A remains the same same

B moves to the right same

C moves to the left same

D moves to the right different

E moves to the left different

(i) Change: increase the temperature of the equilibrium mixture at constant pressure.

H2(g) + I2(g) 2Hl(g)∆Hϴ = +52 kJ mol–1 (1)

(ii) Change: increase the total pressure of the equilibrium mixture at constant temperature.

3H2(g) + N2(g) 2NH3(g)∆Hϴ = -92 kJ mol–1 (1)

(iii) Change: add a catalyst to the equilibrium mixture at constant temperature.

CO(g) + H2O(g) CO2(g) + H2(g)∆Hϴ = -41 kJ mol–1 (1)

(iv) Change: add chlorine to the equilibrium mixture at constant temperature.

PCl5(g) PCl3(g) + Cl2(g)∆Hϴ = +93 kJ mol–1 (1)

(Total 10 marks)

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Q6. A student investigated the chemistry of the halogens and the halide ions.

(a) In the first two tests, the student made the following observations.

Test Observation

1. Add chlorine water to aqueous potassium iodide solution.

The colourless solution turned a brown colour.

2. Add silver nitrate solution to aqueous potassium chloride solution.

The colourless solution produced a white precipitate.

(i) Identify the species responsible for the brown colour in Test 1.

Write the simplest ionic equation for the reaction that has taken place in Test 1.

State the type of reaction that has taken place in Test 1.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(ii) Name the species responsible for the white precipitate in Test 2.

Write the simplest ionic equation for the reaction that has taken place in Test 2.

State what would be observed when an excess of dilute ammonia solution is added to the white precipitate obtained in Test 2.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

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(b) In two further tests, the student made the following observations.

Test Observation

3. Add concentrated sulfuric acid to solid potassium chloride.

The white solid produced misty white fumes which turned blue litmus paper to red.

4. Add concentrated sulfuric acid to solid potassium iodide.

The white solid turned black. A gas was released that smelled of rotten eggs. A yellow solid was formed.

(i) Write the simplest ionic equation for the reaction that has taken place in Test 3.

Identify the species responsible for the misty white fumes produced in Test 3.

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (2)

(ii) The student had read in a textbook that the equation for one of the reactions in Test 4 is as follows.

8H+

+ 8I– + H2SO4 4I2 + H2

S + 4H2

O

Write the two half-equations for this reaction.

State the role of the sulfuric acid and identify the yellow solid that is also observed in Test 4.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (4)

(iii) The student knew that bromine can be used for killing microorganisms in swimming pool water.

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The following equilibrium is established when bromine is added to cold water.

Br2(I) + H2O(I)

HBrO(aq) + H+(aq) + Br–(aq)

Use Le Chatelier’s principle to explain why this equilibrium moves to the right when sodium hydroxide solution is added to a solution containing dissolved bromine.

Deduce why bromine can be used for killing microorganisms in swimming pool water, even though bromine is toxic.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (3)

(Total 15 marks)

Q7. A dynamic equilibrium is established when gas A is mixed with gas B at a given temperature.

A(g) + B(g) C(g) + D(g)

The figure below shows how the concentrations of reactants and products change with time.

(a) (i) On the appropriate axis of the figure, place an X to show the time when equilibrium is first established.

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(1)

(ii) State how the rate of the forward reaction and the rate of the reverse reaction are related to each other at equilibrium.

______________________________________________________________

______________________________________________________________ (1)

(b) Give the meaning of the term dynamic in the context of a dynamic equilibrium.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(c) The total pressure on the system is increased at constant temperature.

(i) State and explain the effect, if any, of this change on the position of this equilibrium.

Effect _________________________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) State and explain the effect, if any, of this change on the time taken to reach this equilibrium.

Effect _________________________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(Total 8 marks)

Q8. Methanol (CH3OH) is an important fuel that can be synthesised from carbon dioxide.

(a) The table shows some standard enthalpies of formation.

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CO2(g) H2(g) CH3OH(g) H2O(g)

∆HfƟ/kJ mol–1 – 394 0 – 201 – 242

(i) Use these standard enthalpies of formation to calculate a value for the standard enthalpy change of this synthesis.

CO2(g) + 3H2(g)

CH3OH(g) + H2O(g)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) State why the standard enthalpy of formation for hydrogen gas is zero.

______________________________________________________________

______________________________________________________________ (1)

(b) State and explain what happens to the yield of methanol when the total pressure is increased in this synthesis.

CO2(g) + 3H2(g)

CH3OH(g) + H2O(g)

Effect on yield _______________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(c) The hydrogen required for this synthesis is formed from methane and steam in a reversible reaction. The equation for this reaction is shown below.

CH4(g) + H2O(g) C0(g) + 3H2(g) ∆H = +206 kJ mol–1

State and explain what happens to the yield of hydrogen in this reaction when the temperature is increased.

Effect on yield _______________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (3)

(d) The methanol produced by this synthesis has been described as a carbon-neutral fuel.


______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(Extra space) ___________________________________________________

______________________________________________________________ (1)

(ii) Write an equation for the complete combustion of methanol.

______________________________________________________________ (1)

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(iii) The equation for the synthesis of methanol is shown below.

CO2(g) + 3H2(g)

CH3OH(g) + H2O(g)

Use this equation and your answer to part (d)(ii) to deduce an equation to represent the overall chemical change that occurs when methanol behaves as a carbon-neutral fuel.

Equation ___________________________________________________ (1)

(e) A student carried out an experiment to determine the enthalpy change when a sample of methanol was burned.

The student found that the temperature of 140 g of water increased by 7.5 °C when 0.011 mol of methanol was burned in air and the heat produced was used to warm the water.

Use the student’s results to calculate a value, in kJ mol–1, for the enthalpy change when one mole of methanol was burned. (The specific heat capacity of water is 4.18 J K–1 g–1).

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 16 marks)

Q9. Esters are produced by the reaction of alcohols with other esters and by the reaction of alcohols with carboxylic acids.

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(a) The esters which make up biodiesel are produced industrially from the esters in vegetable oils.

(i) Complete the equation for this formation of biodiesel.

(2)

(ii) Write an equation for the complete combustion of C17H35COOCH3.

______________________________________________________________ (2)

(b) The ester commonly known as diethyl malonate (DEM) occurs in strawberries and grapes. It can be prepared from acid A according to the following equilibrium.

(i) A mixture of 2.50 mol of A and 10.0 mol of ethanol was left to reach equilibrium in an inert solvent in the presence of a small amount of concentrated sulfuric acid. The equilibrium mixture formed contained 1.80 mol of DEM in a total volume, V dm3, of solution.

Calculate the amount (in moles) of A, of ethanol and of water in this equilibrium mixture.

Moles of A ____________________________________________________

Moles of ethanol _______________________________________________

Moles of water _________________________________________________ (3)

(ii) The total volume of the mixture in part (b)(i) was doubled by the addition of more of the inert solvent.

State and explain the effect of this addition on the equilibrium yield of DEM.

Effect _________________________________________________________

Explanation ____________________________________________________

______________________________________________________________ (2)

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(iii) Using A to represent the acid and DEM to represent the ester, write an expression for the equilibrium constant Kc for the reaction.

______________________________________________________________

______________________________________________________________ (1)

(iv) In a second experiment, the equilibrium mixture was found to contain 0.85 mol of A, 7.2 mol of ethanol, 2.1 mol of DEM and 3.4 mol of water.

Calculate a value of Kc for the reaction and deduce its units.

Calculation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Units _________________________________________________________

______________________________________________________________ (3)

(Total 13 marks)

Q10. A study of equilibrium is important for understanding chemical reactions.

(a) State le Chatelier’s principle.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (1)

(b) Catalysts play an important role in many reactions.

(i) State the meaning of the term catalyst. Explain, in general terms, how catalysts work.

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Meaning of the term catalyst _______________________________________

______________________________________________________________

______________________________________________________________

How catalysts work ______________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(Extra space) ___________________________________________________

______________________________________________________________

(ii) State the effect, if any, of a catalyst on the time taken to reach equilibrium.

______________________________________________________________ (1)

(iii) State the effect, if any, of a catalyst on the position of an equilibrium.

______________________________________________________________ (1)

(c) Consider the following equilibrium reactions.

ΔHᶿ / kJ mol−1

P H2(g) + l2(g) 2Hl(g) −10

Q CO2(g) + 3H2(g) CH3OH(g) + H2O(g) −49

R N2O4(g) 2NO2(g) +58

S N2(g) + 3H2(g) 2NH3(g) −92

T C2H4(g) + H2O(g) CH3CH2OH(g) −42

In each of parts (c)(i) to (c)(v), you should record in the box one of the letters, P, Q, R, S or T, that corresponds to the equilibrium that best fits the information provided. You may use each letter once, more than once or not at all.

(i) A decrease in temperature at constant pressure shifts the position of this equilibrium from right to left.

(1)

(ii) This equilibrium uses concentrated phosphoric acid as a catalyst in a hydration reaction.

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(1)

(iii) A decrease in pressure at constant temperature shifts the position of this equilibrium from left to right.

(1)

(iv) There is no change in the position of this equilibrium when the pressure is increased at constant temperature.

(1)

(v) An increase in the concentration of steam at constant temperature and constant pressure shifts the position of this equilibrium from right to left.

(1)

(Total 11 marks)

Q11. Ethanol is an important industrial compound.

(a) Ethanol can be produced by the hydration of ethene. The equation for the equilibrium that is established is

H2C=CH2(g) + H2O(g) CH3CH2OH(g) ΔH = −42 kJ mol−1

The operating conditions for the process are a temperature of 300 oC and a pressure of 7 MPa. Under these conditions, the conversion of ethene into ethanol is 5%.

(i) Identify the catalyst used in this process. Deduce how an overall yield of 95% is achieved in this process without changing the operating conditions.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) Use your knowledge of equilibrium reactions to explain why a manufacturer might consider using an excess of steam in this process, under the same operating conditions.

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______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(iii) At pressures higher than 7 MPa, some of the ethene reacts to form a solid with a relative molecular mass greater than 5000.

Deduce the identity of this solid.

Give one other reason for not operating this process at pressures higher than 7 MPa. Do not include safety reasons.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(b) Write an equation for the reaction that has an enthalpy change that is the standard enthalpy of formation of ethanol.

___________________________________________________________________ (2)

(c) When ethanol is used as a fuel, it undergoes combustion.


______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Consider these bond enthalpy data.

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C–H C–C C–O O=O C=O O–H

Bond enthalpy / kJ mol−1 412 348 360 496 805 463

Use these data and the equation to calculate a value for the enthalpy of combustion of gaseous ethanol.

CH3CH2OH(g) + 3O2(g) 2CO2(g) + 3H2O(g)

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(d) Gaseous ethanol can be used to convert hot copper(II) oxide into copper.

(i) Deduce the role of ethanol in this reaction.

______________________________________________________________ (1)

(ii) Draw the structure of the organic compound with Mr = 60 that is produced in this reaction.


Q12. This question is about the gaseous equilibrium between compounds E, F and G as shown in the equation.

E (g) + 2F(g) 2G(g) ΔH = –50 kJ mol–1

(a) A 2.0 mol sample of E was heated in a sealed container with a 1.0 mol sample of F. Equilibrium was established at a given temperature and the equilibrium mixture formed contained 0.80 mol of G.

Calculate the amount, in moles, of E and of F in this equilibrium mixture.

Moles of E __________________________________________________________

Moles of F __________________________________________________________ (2)

(b) Write an expression for the equilibrium constant Kc for this equilibrium. State the units of Kc

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Expression _________________________________________________________

___________________________________________________________________

___________________________________________________________________

Units ______________________________________________________________

___________________________________________________________________ (2)

(c) A different mixture of E and F reached equilibrium at temperature T1 in a container ofvolume 1.50 dm3. This equilibrium mixture contained 2.50 mol of E, 1.20 mol of F and 0.85 mol of G.

Calculate a value of Kc for the equilibrium at temperature T1

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) The mixture in part (c) was allowed to reach equilibrium at temperature T1 in a different container of volume 3.00 dm3.

State whether the amount of G in the equilibrium mixture will increase, decrease or stay the same. Explain your answer.

Effect on the amount of G ______________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(e) The mixture in part (c) was allowed to reach equilibrium at temperature T2 in the original container of volume 1.50 dm3.

The value of Kc for the equilibrium was found to have increased.

State and explain which of T1 or T2 is the higher temperature.


Explanation _________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (3)

(Total 12 marks)

Q13. A and B react together in this reversible reaction.

A + 3B ⇌ C + 2D

A mixture of 10 mol of A and 10 mol of B were left to reach equilibrium. The equilibrium mixture contained 4 mol of B.

What is the total amount, in moles, of substances in the equilibrium mixture?

A 14

B 16

C 18

D 20 (Total 1 mark)

Q14. Sulfur dioxide reacts with oxygen to form sulfur trioxide according to the equation

2SO2(g) + O2(g) 2SO3(g)

(a) Write an expression for the equilibrium constant, Kc, for this reaction and deduce its units.

Kc ________________________________________________________________

___________________________________________________________________

Units ______________________________________________________________

___________________________________________________________________ (2)

(b) Samples of sulfur dioxide, oxygen and sulfur trioxide were added to a flask of volume 1.40 dm3 and allowed to reach equilibrium at a given temperature. The flask contained 0.0550 mol of sulfur dioxide and 0.0720 mol of sulfur trioxide at equilibrium. Kc has the numerical value of 27.9 under these conditions.

Calculate the amount, in moles, of oxygen gas in this equilibrium mixture.

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) The experiment in (b) was repeated with the same amounts of sulfur dioxide, oxygen and sulfur trioxide at the same temperature but in a smaller flask. The mixture was allowed to reach equilibrium.

(i) State the effect, if any, of using a smaller flask on the value of Kc

______________________________________________________________ (1)

(ii) State the effect, if any, of using a smaller flask on the amount of sulfur trioxide at equilibrium. Explain your answer.

Effect _________________________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(Total 9 marks)

Q15. Hydrogen is produced in industry from methane and steam in a two-stage process.

(a) In the first stage, carbon monoxide and hydrogen are formed. The equation for this reaction is

CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH = +206 kJ mol−1

(i) Use Le Chatelier’s principle to state whether a high or low temperature should be used to obtain the highest possible equilibrium yield of hydrogen from this first stage. Explain your answer.

Temperature ___________________________________________________

Explanation ____________________________________________________

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______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) Le Chatelier’s principle suggests that a high pressure will produce a low yield of hydrogen in this first stage.

Explain, in terms of the behaviour of particles, why a high operating pressure is used in industry.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(iii) A nickel catalyst is used in the first stage.

Explain why the catalyst is more effective when coated onto an unreactive honeycomb.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(b) The second stage is carried out in a separate reactor. Carbon monoxide is converted into carbon dioxide and more hydrogen is formed.

The equation for this reaction is

CO(g) + H2O(g) CO2(g) + H2(g) ΔH = −41 kJ mol−1

Use Le Chatelier’s principle to state the effect, if any, of a decrease in the total pressure on the yield of hydrogen in this second stage. Explain your answer.

Effect ______________________________________________________________

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Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 9 marks)

Q16. Hydrogen is produced by the reaction of methane with steam. The reaction mixture reaches a state of dynamic equilibrium.

CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g) ∆H = +206 kJ mol−1

Which of the following shows how the equilibrium yield of hydrogen and the value of the equilibrium constant are affected by the changes shown?

Change Effect on

equilibrium yield of H2(g)

Effect on value of Kc

A Increase pressure decrease decrease

B Add a catalyst increase no effect

C Increase temperature increase increase

D Remove CO(g) as formed increase increase (Total 1 mark)

Q17. Iodide ions are present in seawater but at very low concentrations. Certain types of seaweed are able to extract and concentrate iodide ions in their cells up to about 3% by mass. This seaweed could be a source of the element iodine (I2).

The following is an account of a method that was used to extract I2 from Laminaria seaweed. The solvent tetrachloromethane (CCl4) is no longer used because it is very toxic.

A. Collect and dry some seaweed. Heat it very strongly in a crucible until a small quantity of ash is formed.

B. Add distilled or deionised water to the cooled ash in a beaker. Boil the suspension for 5 minutes. Allow to cool.

C. Filter the suspension. D. Gradually add dilute sulfuric acid to the filtrate until the solution is acidic. E. Add hydrogen peroxide solution. A brown solution will be formed. F. Transfer the solution to a separating funnel. G. Add CCl4 to the funnel. It forms a separate organic layer. This organic layer changes

from a colourless liquid to a purple solution. H. Add the organic layer to an evaporating basin and place this in a fume cupboard.

Grey-black crystals of iodine will form as the solvent evaporates.

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(a) In Step A of the method, explain how it could have been confirmed that the decomposition of the seaweed was complete.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) The suspension was filtered in Step C. Suggest an advantage of using vacuum filtration for this part of the method.

___________________________________________________________________

___________________________________________________________________ (1)

(c) Describe how, in Step D, the solution could have been tested to show when it became acidic. Your method should not contaminate the solution.

___________________________________________________________________

___________________________________________________________________ (2)

(d) Write an overall equation showing the oxidation of iodide ions to iodine in Step E using hydrogen peroxide solution in acidic conditions. (No oxygen is evolved in this reaction.)

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(e) A diagram of a separating funnel is shown below.

Aqueous solutions and tetrachloromethane are immiscible. When added to the separating funnel they form two layers as shown in the diagram. Prolonged shaking of

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the mixture allows iodine (dissolved in the aqueous layer) to pass into the tetrachloromethane layer. The densities of some liquids are shown in the table.

Liquid H2O Filtrate from Step C CCl4

Concentrated H2SO4

Density / g cm–3 1.0 1.2 1.6 1.8

Explain briefly whether the upper layer or the lower layer in the separating funnel is likely to show a purple colouration after Step G.

___________________________________________________________________

___________________________________________________________________ (1)

(f) The iodine in the separating funnel quickly establishes an equilibrium after shaking the contents. The concentrations of iodine in the aqueous layer and in the CCl4 layer become constant. This is shown by the relationship

A sample of Laminaria seaweed, mass 56.4 g, was processed by the method given. After Step H, 1.673 g of iodine remained in the evaporating basin. The volume of each layer was 50.0 cm3. The seaweed contains 3.00% iodine by mass.

Calculate the value of K from these data. Show your working.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(g) It has been suggested that cyclohexene could be used to extract the iodine from the aqueous layer. Explain why this would not be a suitable solvent.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(h) The iodine produced at the end of Step H is impure and needs to be recrystallised from a suitable inert solvent. Explain the essential feature to consider when choosing a suitable inert solvent for this recrystallisation.

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (2)

(Total 14 marks)

Q18. Ethene reacts with steam in the presence of an acid catalyst to form ethanol.

CH2=CH2(g) + H2O(g) ⇌ CH3CH2OH(g)

(a) Write an expression for the equilibrium constant Kc for this equilibrium. Deduce the units of Kc.

Expression _________________________________________________________

___________________________________________________________________

___________________________________________________________________

Units ______________________________________________________________ (2)

(b) An equilibrium mixture was found to contain 0.700 mol of ethene, 1.20 mol of steam and 4.40 mol of ethanol at a temperature T. The volume of the container was 2.00 dm3.

Calculate a value of Kc for this equilibrium at this temperature.

Give your answer to an appropriate number of significant figures.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 4 marks)

Q19. A pale brown mixture of NO2 and N2O4 is allowed to reach equilibrium in a sealed gas syringe according to the following equation.

2NO2(g) ⇌ N2O4(g)

When the plunger is pushed further into the syringe the pressure increases and the mixture becomes paler in colour.

When the syringe is placed in a hot oven the mixture becomes darker in colour.

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Which of the following statements is correct?

A NO2 is brown and the forward reaction is exothermic.

B NO2 is brown and the forward reaction is endothermic.

C NO2 is colourless and the forward reaction is exothermic.

D NO2 is colourless and the forward reaction is endothermic. (Total 1 mark)

Q20. Ethanol and ethanoic acid react reversibly to form ethyl ethanoate and water according to the equation:

CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O

A mixture of 8.00 × 10–2 mol of ethanoic acid and 1.20 × 10–1 mol of ethanol is allowed to reach equilibrium at 20 °C.

• The equilibrium mixture is placed in a graduated flask and the volume made up to 250 cm3 with distilled water.

• A 10.0 cm3 sample of this equilibrium mixture is titrated with sodium hydroxide added from a burette.

• The ethanoic acid in this sample reacts with 3.20 cm3 of 2.00 × 10–1 mol dm–3 sodium hydroxide solution.

(a) Calculate the value for Kc for the reaction of ethanoic acid and ethanol at 20 °C. Give your answer to the appropriate number of significant figures.

Kc ____________________ (6)

(b) A student obtained the titration results given in Table 1.

Table 1

Rough 1 2 3



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Titre / cm3

Complete Table 1. (1)

(c) Calculate the mean titre and justify your choice of titres.

Calculation

Mean titre = ____________________cm3

Justification _________________________________________________________

___________________________________________________________________ (2)

(d) The pH ranges of three indicators are shown in Table 2.

Table 2

Indicator pH range

Bromocresol green 3.8–5.4

Bromothymol blue 6.0–7.6

Thymol blue 8.0–9.6

Select from Table 2 a suitable indicator for the titration of ethanoic acid with sodium hydroxide.

___________________________________________________________________ (1)

(e) The uncertainty in the mean titre for this experiment is ±0.15 cm3.

Calculate the percentage uncertainty in this mean titre.

Percentage uncertainty = ____________________ % (1)

(f) Suggest how, using the same mass of ethanoic acid, the experiment could be improved to reduce the percentage uncertainty.

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 13 marks)

Q21. Acid X reacts with methanol to form an ester Y.

(a) Write an expression for the equilibrium constant, Kc, for this reaction. Use X and Y in your expression.

___________________________________________________________________

___________________________________________________________________ (1)

(b) A mixture of 0.32 mol of acid X and 0.84 mol of CH3OH was allowed to reach equilibrium in the presence of a small amount of catalyst. The equilibrium mixture formed contained 0.26 mol of ester Y.

Calculate the amounts, in moles, of X, CH3OH and H2O in this equilibrium mixture.

Amount of X ________________________________________________________

Amount of CH3OH ____________________________________________________

Amount of H2O ______________________________________________________ (3)

(c) Calculate the value of Kc and state the units.

Kc ______________ units _______ (3)

(d) Predict the effect on Kc if the reaction is carried out at a lower temperature.

___________________________________________________________________ (1)

(Total 8 marks)

Q22. When one mole of ammonia is heated to a given temperature, 50% of the compound

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dissociates and the following equilibrium is established.

NH3(g) N2(g) + H2(g)

What is the total number of moles of gas present in this equilibrium mixture?

A 1.5

B 2.0

C 2.5


Q23. Many chemical processes release waste products into the atmosphere. Scientists are developing new solid catalysts to convert more efficiently these emissions into useful products, such as fuels. One example is a catalyst to convert these emissions into methanol. The catalyst is thought to work by breaking a H–H bond.

An equation for this formation of methanol is given below.


Some mean bond enthalpies are shown in the following table.

Bond C=O C–H C–O O–H

Mean bond enthalpy / kJ mol−1 743 412 360 463

(a) Use the enthalpy change for the reaction and data from the table to calculate a value for the H–H bond enthalpy.

H–H bond enthalpy = _______________ kJ mol−1

(3)

(b) A data book value for the H–H bond enthalpy is 436 kJ mol−1.

Suggest one reason why this value is different from your answer to part (a).

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________ (1)

(c) Suggest one environmental advantage of manufacturing methanol fuel by this reaction.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(d) Use Le Chatelier's principle to justify why the reaction is carried out at a high pressure rather than at atmospheric pressure.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(e) Suggest why the catalyst used in this process may become less efficient if the carbon dioxide and hydrogen contain impurities.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (1)

(f) In a laboratory experiment to investigate the reaction shown in the equation below, 1.0 mol of carbon dioxide and 3.0 mol of hydrogen were sealed into a container. After the mixture had reached equilibrium, at a pressure of 500 kPa, the yield of methanol was 0.86 mol.

CO2(g) + 3H2(g) CH3OH(g) + H2O(g)

Calculate a value for Kp

Give your answer to the appropriate number of significant figures. Give units with your answer.

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Kp = _______________ Units = _______________ (7)

(Total 16 marks)



Name _____________________________________________________________


(2)


___________________________________________________________________ (1)

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(c) Name polymer Y.

___________________________________________________________________ (1)



___________________________________________________________________ (1)



___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(Total 11 marks)

Q25. A student carried out an experiment to determine the value of the equilibrium constant (Kc) for the esterification reaction between ethanoic acid and ethanol.

ethanoic acid + ethanol ⇌ ethyl ethanoate + water

(a) Write an equation for this reaction.

___________________________________________________________________ (1)

(b) Draw the skeletal formula of ethyl ethanoate.

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___________________________________________________________________ (1)

(c) The student used a small amount of concentrated sulfuric acid as a catalyst to increase the rate of the reaction.

State, in general terms, how a catalyst works.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(d) The student mixed 0.0435 mol of ethanol and 0.0435 mol of ethanoic acid. The student added 5.00 × 10−4 mol of sulfuric acid to the mixture. This mixture was left for one week to reach equilibrium. The equilibrium reaction was stopped by adding the mixture to water.

For this reaction, Kc = 4.07 at the temperature of the experiment.

Calculate the volume of 0.400 mol dm−3 sodium hydroxide solution required to react completely with the acids in the equilibrium mixture.

Volume = __________________ cm3

(6)

(e) Suggest how the student could check that the mixture had reached equilibrium after one week.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (2)

(Total 12 marks)

Q26. Colourless solutions of X(aq) and Y(aq) react to form an orange solution of Z(aq) according to the following equation.

X(aq) + 2Y(aq) Z(aq) ΔH = −20 kJ mol−1

A student added a solution containing 0.50 mol of X(aq) to a solution containing 0.50 mol of Y(aq) and shook the mixture. After 30 seconds, there was no further change in colour. The amount of Z(aq) at equilibrium was 0.20 mol.

(a) Deduce the amounts of X(aq) and Y(aq) at equilibrium.

Amount of X(aq) = ________ mol Amount of Y(aq) = ________ mol (2)

(b) On the grid below, draw a graph to show how the amount of Z(aq) changed from the time of initial mixing until 60 seconds had elapsed.

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(3)

(c) The student prepared another equilibrium mixture in which the equilibrium concentrations of X and Z were: X(aq) = 0.40 mol dm−3 and Z(aq) = 0.35 mol dm−3.

For this reaction, the equilibrium constant Kc = 2.9 mol−2 dm6. Calculate a value for the concentration of Y at equilibrium. Give your answer to the appropriate number of significant figures.

[Y] = ____________________ mol dm−3

(3)

(d) The student added a few drops of Y(aq) to the equilibrium mixture of X(aq), Y(aq) and Z(aq) in part (c).

Suggest how the colour of the mixture changed. Give a reason for your answer.

Colour change_______________________________________________________

Reason ____________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________ (3)

(e) The student warmed the equilibrium mixture from part (c).

Predict the colour change, if any, when the equilibrium mixture was warmed.

___________________________________________________________________

___________________________________________________________________ (1)

(Total 12 marks)

Q27. There are several stages in the industrial production of methanol from methane.

(a) The first stage involves a gaseous equilibrium between the reactants (methane and steam), and some gaseous products. Figures 1 and 2 show the percentage conversion of methane into the gaseous products under different conditions at equilibrium.

Deduce the optimum conditions for the industrial conversion of methane and steam into the gaseous products.

Explain your deductions.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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(6)

(b) The equation shows the final stage in the production of methanol.

CO(g) + 2H2(g) ⇌ CH3OH(g)

20.1  mol of carbon monoxide and 24.2  mol of hydrogen were placed in a sealed container. An equilibrium was established at 600  K. The equilibrium mixture contained 2.16  mol of methanol.

Calculate the amount, in moles, of carbon monoxide and of hydrogen in the equilibrium mixture.

Amount of carbon monoxide = ____________________ mol

Amount of hydrogen = ____________________ mol (2)

(c) A different mixture of carbon monoxide and hydrogen was allowed to reach equilibrium at 600 K

At equilibrium, the mixture contained 2.76  mol of carbon monoxide, 4.51  mol of hydrogen and 0.360  mol of methanol. The total pressure was 630  kPa

Calculate a value for the equilibrium constant, Kp, for this reaction at 600  K and state its units.

Value of Kp ____________________ Units ____________________ (6)

(Total 14 marks)

Q28. Hydrogen can be manufactured by the reaction of methane with steam. An equilibrium is established as shown by the equation.

CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)

(a) Use Le Chatelier’s principle to predict the effect on the equilibrium yield of hydrogen if the overall pressure is increased. Explain your answer.

Effect on yield _______________________________________________________

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Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Explain why the equilibrium yield of hydrogen is unchanged if a catalyst is used in the reaction.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) The table shows the standard enthalpy of formation and the standard entropy for each substance in this equilibrium reaction.

CH4(g) H2O(g) CO(g) H2(g)

ΔfHθ / kJ mol−1 −75 −242 −111 0

Sθ / J K−1 mol−1 186 189 198 131

Use data from the table to calculate the standard enthalpy change for this equilibrium reaction.

Standard enthalpy change _____________ kJ mol−1

(2)

Use your answer from part (c) and the entropy data from the table above to calculate the minimum temperature, in °C, needed for this reaction to be feasible. Give your answer to the appropriate number of significant figures.

(If you did not complete part (c) you should assume a value of 120 kJ mol−1 for the standard enthalpy change. This is not the correct value).

Minimum temperature _________ °C (5)

(Total 12 marks)

Q29. Methanol can be manufactured by the reaction of carbon monoxide with hydrogen

CO(g) + 2H2(g) ⇌ CH3OH(g)

In an experiment, 0.73 mol of carbon monoxide was heated with 1.25 mol of hydrogen. An equilibrium mixture was formed that contained 0.43 mol of methanol.

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(a) Calculate the amount, in moles, of each reactant present at equilibrium.

Amount of carbon monoxide = ____ mol

Amount of hydrogen = ___________ mol (2)

(b) Write an expression for the equilibrium constant, Kc, for this reaction.

___________________________________________________________________ (1)

(c) In another experiment at a different temperature, the equilibrium mixture contained 0.452 mol of carbon monoxide, 0.106 mol of hydrogen and 0.273 mol of methanol in a flask of volume 9.40 × 103 cm3.

Calculate the value of the equilibrium constant, Kc, at this temperature and state the units.

Kc = __________ Units = __________ (4)

(d) The total pressure of this equilibrium mixture in the flask was 482.9 kPa.

Calculate the temperature, in °C, of the equilibrium mixture. (The ideal gas constant R = 8.31 J mol−1 K−1)

Temperature = ________________ °C (4)

(Total 11 marks)

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Q30. The following equilibrium was established in a container with volume V cm3 at 393 K and 200 kPa.

M2(g) + R(g) ⇌ RM2(g) ΔH = +150 kJ mol−1

Which change would increase the yield of RM2?

A change the pressure to 150 kPa

B change the temperature to 293 K

C remove RM2 as it is formed

D change the volume of the vessel to 2V cm3

(Total 1 mark)

Q31. Ethanoic acid and ethane-1,2-diol react together to form the diester (C6H10O4) as shown.

2CH3COOH(l) + HOCH2CH2OH(l) ⇌ C6H10O4(l) + 2H2O(l)

(a) Draw a structural formula for the diester C6H10O4

(1)

(b) A small amount of catalyst was added to a mixture of 0.470 mol of ethanoic acid and 0.205 mol of ethane-1,2-diol.

The mixture was left to reach equilibrium at a constant temperature.

Complete Table 1.

Table 1

Amount in the mixture / mol

CH3COOH HOCH2CH2OH C6H10O4 H2O

At the start 0.470 0.205 0 0

At equilibrium 0.180

Space for working

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(3)

(c) Write an expression for the equilibrium constant, Kc, for the reaction.

The total volume of the mixture does not need to be measured to allow a correct value for Kc to be calculated.

Justify this statement.

Expression

Justification _________________________________________________________

___________________________________________________________________ (2)

(d) A different mixture of ethanoic acid, ethane-1,2-diol and water was prepared and left to reach equilibrium at a different temperature from the experiment in part (b)

The amounts present in the new equilibrium mixture are shown in Table 2. Table 2

Amount in the mixture / mol

CH3COOH HOCH2CH2OH C6H10O4 H2O

At new equilibrium

To be calculated 0.264 0.802 1.15

The value of Kc was 6.45 at this different temperature.

Use this value and the data in Table 2 to calculate the amount, in mol, of ethanoic acid present in the new equilibrium mixture.


Amount of ethanoic acid ____________________ mol (3)

(Total 9 marks)

Q32.

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Hydrogen can be produced by this reaction.

CO(g) + H2O(g) ⇌ CO2(g) + H2(g)

In an experiment 4.20 mol of carbon monoxide were mixed with 2.00 mol of steam. When the reaction reached equilibrium, 1.60 mol of hydrogen had been formed.

What is the value of the equilibrium constant, Kc, for this reaction?

A 0.30

B 0.41

C 1.54


Q33. The forward reaction in this equilibrium is endothermic

COCl2 (g) ⇌ CO(g) + Cl2 (g)

Which statement is correct?

A If the total pressure is increased at constant temperature, the proportion of COCl2 in the equilibrium mixture will decrease

B Use of a catalyst will increase the proportion of COCl2 in the equilibrium mixture at constant temperature and pressure

C Reducing the equilibrium concentration of CO will increase the value of the equilibrium constant

D Raising the temperature from 373 K to 473 K will increase the value of the equilibrium constant

(Total 1 mark)

Q34. When substances P and Q react together to form substance R an equilibrium is established according to the equation

P(g) + Q(g) ⇌ 2R(g)

The equilibrium constant expression is Kc =

1.0 mol of P and 1.0 mol of Q were mixed in a container with volume 1.0 dm3

At equilibrium, x mol of P had reacted.

(a) The amount, in moles, of each of P and Q at equilibrium is (1− x).

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Deduce in terms of x the amount, in moles, of R in the equilibrium mixture.

___________________________________________________________________ (1)

(b) At 298 K the value of the equilibrium constant Kc = 3.6

Calculate a value for the equilibrium concentration, in mol dm−3, of R.

Equilibrium concentration of R ____________________ mol dm−3

(3) (Total 4 marks)

Q35. Methanol, for use as a fuel, can be produced by the reaction of carbon monoxide with hydrogen.

CO(g) + 2H2(g) ⇌ CH3OH(g) ΔH = –90 kJ mol–1

The reaction is typically carried out at 300 °C and 3 × 107 Pa, in the presence of a catalyst.

(a) The graph shows the Maxwell–Boltzmann distribution for a mixture of carbon monoxide and hydrogen at 300 °C.

(i) Sketch a second curve on the graph to show the distribution of molecular energies in this mixture at a higher temperature.

(1)

(ii) Explain with reference to both curves on the graph how a small change in temperature leads to a large change in the rate of reaction.

______________________________________________________________

______________________________________________________________

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______________________________________________________________

______________________________________________________________ (2)

(b) Both the rate of production and equilibrium yield of methanol are considered when choosing the most appropriate conditions for the operation of this process on an industrial scale.

(i) State and explain the effect of a higher pressure on the equilibrium yield of methanol.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (3)

(ii) By considering both rate and yield, state why the reaction is carried out at a temperature of 300 °C rather than at a higher temperature.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(Total 8 marks)

Q36.

The following equilibrium is established between colourless dinitrogen tetraoxide gas (N2O4) and dark brown nitrogen dioxide gas.

N2O4(g) 2NO2(g) ΔH = 58 kJ mol–1

(i) Give two features of a reaction at equilibrium.

Feature 1 ______________________________________________________

______________________________________________________________

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______________________________________________________________

______________________________________________________________

Feature 2 ______________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(ii) Use Le Chatelier’s principle to explain why the mixture of gases becomes darker in colour when the mixture is heated at constant pressure.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(iii) Use Le Chatelier’s principle to explain why the amount of NO2 decreases when the pressure is increased at constant temperature.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(Total 6 marks)

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Mark schemes

Q1. (a) Cl2 0.4

1

NOCl 1.7 1

(b) (i) Kc=

Penalise expression containing V Allow ( ) here, but must have all brackets. If Kc expression wrong, max 2 in (b)(ii) for M1 for correct rearrangement of their Kc and M4 for multiplying by 15

1

(ii) M1

Mark is for rearrangement of correct Kc expression. If Kc rearrangement wrong, can only score max 2 for: M3 and M4

1

M2

Rounding 1.90 / 15 wrongly to 0.126 is AE

1

M3 [Cl2] = 0.0361 to 0.0365 (min 2 sfs) Mark for correct calculation of [Cl2]

1

M4 mol Cl2 = 0.54 to 0.55 Correct answer scores 4 ignore working Mark is for answer of (M3 × 15)

1

(iii) ( �(7.4 × 10−3) = ) 0.086

Allow 0.085 to 0.086) Mark for answer OR conseq on their Cl2

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Or 1

mol ½ dm−3/2 OR mol 0.5 dm −1.5

NOT 1

[9]

Q2.

Q3. (a) In either order

For M1 accept [ ] for concentration

M1 Concentrations (of reactants and products) remain or stay constant / the same NOT “equal concentrations” and NOT “concentration(s) is / are the same”

M2 Forward rate = Reverse / backward rate NOT “amount”

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Ignore “dynamic” and ignore “speed” Ignore “closed system” It is possible to score both marks under the heading of a single feature

2

(b) M1 Catalysts increase rate of / speed up both forward and reverse / backward reactions

If M1 is given as “no effect” / “no change” then CE= 0 for clip

M2 increase in rate / affect on rate / speed is equal / the same Ignore references to “decrease in rate”

2

(c) (i) M1 (The yield) increases / goes up / gets more If M1 is given as “decreases” / “no effect” / “no change” then CE= 0 for clip, but mark on from a blank.

M2 There are more moles / molecules (of gas) on the left / of reactants Ignore “volumes”, “articles” “atoms” and “species” for M2

OR fewer moles / molecules (of gas) on the right / products

OR there are 4 moles / molecules (of gas) on the left and 2 moles / molecules on the right.

OR (equilibrium) shifts / moves to the side with less moles / molecules

M3 Can only score M3 if M2 is correct

The equilibrium shifts / moves (from left to right) to oppose the increase in pressure For M3, not simply “to oppose the change” For M3 credit the equilibrium shifts / moves to lower / decrease the pressure (There must be a specific reference to the change that is opposed)

3

(ii) M1 The yield decreases / goes down / gets less If M1 is given as “increase” / “no effect” / “no change” then CE= 0 for clip, but mark on from a blank.

M2 (Forward) reaction is exothermic OR gives out / releases heat

OR

reverse reaction is endothermic OR takes in / absorbs heat


The equilibrium shifts / moves (from right to left) to oppose the increase in temperature

For M3, not simply “to oppose the change” For M3 credit the equilibrium shifts / moves to absorb the heat OR

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to cool the reaction OR to lower the temperature (There must be a specific reference to the change that is opposed)

3

(d) (i) Must be comparative Credit correct reference to rate being too (s)low / (s)lower at temperatures less than 600 K

Higher rate of reaction

OR increase / speed up the rate (of reaction) Ignore statements about the “yield of ammonia”

OR Gets to equilibrium faster/ quicker

OR faster or quicker rate / speed of attainment of equilibrium 1

(ii) Less electrical pumping cost Not just “less expensive” alone

OR Not just “less energy or saves energy” alone

Use lower pressure equipment / valves / gaskets / piping etc. Credit correct qualified references to higher pressures

OR

Uses less expensive equipment Ignore references to safety

1 [12]

Q4. (a) (i) Mol SO3 = 5.2

1

Mol SO2 = 2.8 1

(ii)

Penalise expression containing numbers or V Allow ( ) but must have all brackets. If brackets missing but otherwise correct, penalise here but mark on

Ignore subsequent correct working If Kc wrong (wrong powers or upside down etc) can only score M1 in (a)(iv)

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1

(iii) mol dm–3

Allow conseq to their wrong Kc 1

(iv) If Kc wrong in (a)(iv) (wrong powers or upside down etc) can only score M1

Values from (a)(i)

or

Alternative values

1

M1 For dividing all three by volume – if volume missed or used wrongly, lose M1 & M2 but can score M3 conseq

M2 insertion of values (allow conseq use of their wrong values from (a)(i)) AE (–1) for copying numbers wrongly or swapping two numbers

1

Values from (a)(i) M3 = 0.0338 or 0.034 (allow 0.03376 to 0.035) Min 2 sfs Ignore units in (a)(iv)

If vol missed score only M3 Values from (a)(i) 0.406 - allow values between 0.40 (if correctly rounded) and 0.41

Alternative values M3 0.0153 or 0.015 (allow 0.015 to 0.017) Min 2 sfs Ignore units in (a)(iv)

from alternative values allow 0.18 to 0.184 1

(b) (i) Increase or more moles (of oxygen) or higher 1

(ii) No change or no effect or none or (remains) same 1

(c) M1 T1

If T2 CE = 0 1

M2 (At Temp,T2, when Kc is lower) Equm/reaction moves to left or

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towards reagent or towards SO3 OR moles SO3 increases 1

M3 This reverse reaction is exothermic,

OR

M3 (forward) reaction is endothermic

M2 if Temp is increased Equm/reaction moves to right or towards product or towards SO2 OR moles SO2 increases

OR

M3 (forward) reaction is endothermic

M2 if Temp is decreased Equm/reaction moves to left or towards reagent or towards SO3 OR moles SO3 increases

1 [12]

Q5. (a) (i) mol H2 = 0.47

1

mol I2 = 0.17 If answers reversed, ie mol H2 = 0.17 mol I2 = 0.47 then allow one mark (for second answer).

1

(ii)

Penalise expression containing V But mark on in (a)(iv)

Penalise missing square brackets in this part (and not elsewhere in paper) but mark on in (a)(iv)

1

(iii) equal number of moles (on each side of equation)

OR

equal moles (top and bottom of Kc expression) 1

(iv)

Ignore V If Kc wrong in (a)(ii) (wrong powers or upside down etc) no marks here

1

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= 52(.1) 1

(b) (i) D 1

(ii) B 1

(iii) A 1

(iv) C 1

[10]

Q6. (a) (i) M1 iodine OR I2 OR I3–

Ignore state symbols Credit M1 for “iodine solution”

M2 Cl2 + 2I – 2Cl – + I2

OR ½ Cl2 + I – Cl – + ½ I2

Penalise multiples in M2 except those shown M2 accept correct use of I3–

M3 redox or reduction-oxidation or displacement 3

(ii) M1 (the white precipitate is) silver chloride M1 must be named and for this mark ignore incorrect formula

M2 Ag+ + Cl – AgCl For M2 ignore state symbols Penalise multiples

M3 (white) precipitate / it dissolves

OR colourless solution Ignore references to “clear” alone

3

(b) (i) M1 H2SO4 + 2Cl – 2HCl + SO42–

For M1 ignore state symbols

OR H2SO4 + Cl– HCl + HSO4–

Penalise multiples for equations and apply the list principle

OR H+ + Cl– HCl

M2 hydrogen chloride OR HCl OR hydrochloric acid 2

(ii) M1 and M2 in either order For M1 and M2, ignore state symbols and credit multiples

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M1 2I – I2 + 2e –

OR

8I – 4I2 + 8e – Do not penalise absence of charge on the electron Credit electrons shown correctly on the other side of each equation

M2 H2SO4 + 8H+ + 8e – H2S + 4H2O

OR

SO42– + 10H+ + 8e – H2S + 4H2O Additional equations should not contradict

M3 oxidising agent / oxidises the iodide (ions)

OR

electron acceptor

M4 sulfur OR S OR S2 OR S8 OR sulphur 4

(iii) M1 The NaOH / OH– / (sodium) hydroxide reacts with / neutralises the H+ / acid / HBr (lowering its concentration)

OR a correct neutralisation equation for H+ or HBr with NaOH or with hydroxide ion Ignore reference to NaOH reacting with bromide ions Ignore reference to NaOH reacting with HBrO alone

M2 Requires a correct statement for M1

The (position of) equilibrium moves / shifts(from L to R)

• to replace the H+ / acid / HBr that has been removed / lost

• OR to increase the H+ / acid / HBr concentration

• OR to make more H+ / acid / HBr / product(s)

• OR to oppose the loss of H+ / loss of product(s)

• OR to oppose the decrease in concentration of product(s) In M2, answers must refer to the (position of) equilibrium shifts / moves and is not enough to state simply that it / the system / the reaction shifts to oppose the change.

M3 The (health) benefit outweighs the risk or wtte

OR

a clear statement that once it has done its job, little of it remains

OR

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used in (very) dilute concentrations / small amounts / low doses 3

[15]

Q7. (a) (i) Award mark for X on the time axis at the point where the lines just become

horizontal Allow this mark if X is above the letters “sh” in the word “show” in part(ii) - in the range of lines 31 to 33.

1

(ii) They are equal / the same

OR

Forward (rate) = Reverse / backward (rate) Allow the word ‘speed’ in this context. Ignore reference to concentration.

1

(b) Both OR forward and reverse reactions occur at the same time

OR both are occurring at once

OR both occur all of the time

OR both are ongoing

OR both never stop Ignore ‘at equal rates’. Ignore reference to concentration or equilibrium. The idea that both reactions occur simultaneously is essential. The simple idea of ‘both reactions occurring’ is insufficient for the mark.

1

(c) (i) M1 No effect / no change / none / stays the same

M2 requires correct M1 In M2, ignore reference to particles or atoms.

M2 Equal (number of) moles / molecules on both sides 2

(ii) M1 Less time or it decreases or (equilibrium) reached faster (ie M1 is a reference to time taken)

If M1 is ‘more time / it increases’ or ‘no effect’, then CE=0 for the clip. Reference to faster / increased rate / increased speed alone penalises M1, but mark on M2 and M3.

M2 More particles / molecules in a given volume / space

OR the particles / molecules are closer together If M1 is blank, then look for all three marks in the text.

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M3 More successful / productive collisions in a given time

OR more collisions with E>EAct in a given time

OR more frequent successful / productive collisions

OR increased / greater successful / productive collision frequency / rate Ignore reference to reactants / products. Penalise M3 if an increase / decrease in the value of EAct is stated.

3 [8]


have all ∆Hsymbols and the ∑ or SUM)

M1 ΔHr = ΣΔHf (products) - ΣΔHf (reactants)

OR a correct cycle of balanced equations with 1C, 3H2 and 1O2

M2 ΔHr = – 201 + (– 242) – (– 394) ΔHr = – 201 – 242 + 394 ΔHr = – 443 + 394 (This also scores M1)

M3 = – 49 (kJ mol–1) (Award 1 mark ONLY for + 49) Correct answer gains full marks Credit 1 mark ONLY for + 49 (kJ mol–1) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either correct cycle of balanced equations with 1C, 3H2 and 1O2

OR a clear statement of M1 which could be in words and scores only M1

3

(ii) It is an element / elemental Ignore reference to “standard state”

OR

By definition 1

(b) M1 (The yield) increases / goes up / gets more If M1 is given as “decreases” / “no effect” / “no change” then CE= 0 for clip, but mark on only M2 and M3 from a blank M1

M2 There are more moles / molecules (of gas) on the left / of reactants

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OR fewer moles / molecules (of gas) on the right / products OR there are 4 moles /molecules (of gas) on the left and 2 moles / molecules on the right. OR (equilibrium) shifts / moves to the side with less moles / molecules

Ignore “volumes”, “particles” “atoms” and “species” for M2

M3: Can only score M3 if M2 is correct

The (position of) equilibrium shifts / moves (from left to right) to oppose the increase in pressure

For M3, not simply “to oppose the change” For M3 credit the equilibrium shifts / moves (to right) to lower / decrease the pressure (There must be a specific reference to the change that is opposed)

3

(c) M1 Yield increases goes up

M2 The (forward) reaction / to the right is endothermic OR takes in/ absorbs heat

OR

The reverse reaction / to the left is exothermic OR gives out / releases heat If M1 is given as “decrease” / “no effect” / “no change” then CE= 0 for clip, but mark on only M2 and M3 from a blank M1


M3 The (position of) equilibrium shifts / moves (from left to right) to oppose the increase in temperature (QoL)

For M3, not simply “to oppose the change” For M3, credit the (position of) equilibrium shifts / moves (QoL) to absorb the heat OR to cool the reaction OR to lower the temperature (There must be a specific reference to the change that is opposed)

3

(d) (i) An activity which has no net / overall (annual) carbon emissions to the atmosphere OR An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere. OR There is no change in the total amount / level of carbon dioxide /CO2 carbon /greenhouse gas present in the atmosphere.

The idea that the carbon /CO2 given out equals the carbon /CO2 that was taken in from the atmosphere

1

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(ii) CH3OH + 1½ O2 CO2 + 2H2O Ignore state symbols Accept multiples

1

(iii) 3H2 + 1½ O2 3H2O Ignore state symbols

OR Accept multiples

2H2 + O2 2H2O Extra species must be crossed through

1

(e) M1 q = m c ∆T Award full marks for correct answer Ignore the case for each letter

OR q = 140 × 4.18 × 7.5

M2 = 4389 (J) OR 4.389 (kJ) OR 4.39 (kJ) OR 4.4 (kJ)(also scores M1)

M3 Using 0.0110 mol therefore ∆H = – 399 (kJmol–1 ) OR – 400

Penalise M3 ONLY if correct numerical answer but sign is incorrect; +399 gains 2 marks Penalise M2 for arithmetic error and mark on In M1, do not penalise incorrect cases in the formula If ∆T = 280.5; score q = m c ∆T only If c = 4.81 (leads to 5050.5) penalise M2 ONLY and mark on for M3 = – 459

+399 or +400 gains 2 marks Ignore incorrect units

3 [16]

Q9. (a) (i) 3CH3OH

Not molecular formula 1

HOCH2CH(OH)CH2OH 1

(ii) → 19CO2 + 19H2O Or doubled

1

C17H35COOCH3 + 27½ or 55/2 O2

Consequential on correct right-hand side 1

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(b) (i) A0.7 1

Ethanol6.4 1

Water3.6 1

(ii) No effect If wrong, CE= 0

1

Equal moles on each side of equation OR V cancels Ignore moles of gas

1

(iii) M1

Must have all brackets but allow ( )

1

(iv) M2

If Kc wrong can only score M4 for units consequential to their Kc working in (b)(iv)

1

M3 0.55 (min 2dp) 1

M4 No units 1

[13]

Q10. (a) (If any factor is changed which affects an equilibrium), the (position of) equilibrium will

shift / move so as to oppose / counteract the change. Must refer to equilibrium Ignore reference to “system” alone A variety of wording will be seen here and the key part is the last phrase

OR

(When a system / reaction in equilibrium is disturbed), the (position of) equilibrium shifts / moves in a direction which tends to reduce the disturbance

An alternative to shift / move would be the idea of changing / altering the position of equilibrium

1

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(b) (i) M1 A substance that speeds up the reaction / alters the rate but is chemically unchanged at the end / not used up

Both ideas needed for M1 Credit can score for M1, M2 and M3 from anywhere within the answer

M2 Catalysts provide an alternative route / alternative pathway / different mechanism

M3 that has a lower activation energy / Ea

OR lowers the activation energy / Ea

3

(ii) (Time is) less / shorter / decreases / reduces Credit “faster”, “speeds up”, “quicker” or words to this effect

1

(iii) None 1

(c) (i) R 1

(ii) T 1

(iii) R 1

(iv) P 1

(v) Q 1

[11]

Q11. (a) (i) M1 c(oncentrated) phosphoric acid / c(onc.) H3PO4

OR c(oncentrated) sulfuric acid / c(onc.) H2SO4

In M1, the acid must be concentrated. Ignore an incorrect attempt at the correct formula that is written in addition to the correct name.

M2 Re-circulate / re-cycle the (unreacted) ethene (and steam) / the reactants OR pass the gases over the catalyst several / many times

In M2, ignore “remove the ethanol”. Credit “re-use”.

2

(ii) M1 (By Le Chatelier’s principle) the equilibrium is driven / shifts / moves to the right / L to R / forwards / in the forward direction

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M2 depends on a correct statement of M1 The equilibrium moves / shifts to

• oppose the addition of / increased concentration of / increased moles / increased amount of water / steam

• to decrease the amount of steam / water

Mark M3 independently M3 Yield of product / conversion increase OR ethanol increases / goes up / gets more

3

(iii) M1 Poly(ethene) / polyethene / polythene / HDPE / LDPE

M2 At higher pressures More / higher cost of electrical energy to pump / pumping cost OR Cost of higher pressure equipment / valves / gaskets / piping etc. OR expensive equipment

Credit all converse arguments for M2 2

(b) M1 for balanced equation

M2 for state symbols in a correctly balanced equation

2C(s / graphite) + 3H2(g) + ½O2(g) CH3CH2OH(l) (C2H5OH)

Not multiples but credit correct state symbols in a correctly balanced equation. Penalise C2H6O but credit correct state symbols in a correctly balanced equation.

2

(c) (i) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / element

If standard enthalpy of formation CE=0


M3 with (all) reactants and products / (all) substances in standard / specified states OR (all) reactants and products / (all) substances in normal states under standard conditions / 100 kPa / 1 bar and specified T / 298 K


3

(ii) M1 Correct answer gains full marks

ΣB(reactants) − ΣB(products) = ΔH Credit 1 mark for (+) 1279 (kJ mol−1)

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OR Sum of bonds broken − Sum of bonds formed = ΔH OR B(C-C) + B(C-O) + B(O-H) + 5B(C-H) + 3B(O=O) (LHS) − 4B(C=O) − 6B(O−H) (RHS) = ΔH

M2 (also scores M1) 348+360+463+5(412)+3(496) [LHS = 4719] (2060) (1488) − 4(805) − 6(463) [RHS = − 5998] = ΔH (3220) (2778) OR using only bonds broken and formed (4256 − 5535)

For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 2C and 6H and 7O OR a clear statement of M1 which could be in words and scores only M1

M3 ΔH= − 1279 (kJ mol−1)

Allow a maximum of one mark if the only scoring point is LHS = 4719 OR RHS = 5998

Award 1 mark for +1279

Candidates may use a cycle and gain full marks 3

(d) (i) Reducing agent OR reductant OR electron donor OR to reduce the copper oxide

Not “reduction”. Not “oxidation”. Not “electron pair donor”.

1

(ii) CH3COOH 1

[17]

Q12. (a) Mol of E 1.6(00)

Ignore extra zeros. 1

Mol of F 0.2(00) 1

(b) Kc = Penalise expression containing V. Penalise missing brackets or ( ).

1

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mol−1 dm3

If Kc wrong, allow units consequential to their Kc, but no marks in (c) unless correct Kc used in (c).

1

(c) Kc = Vol missed or used wrongly – no marks. If Kc correct in (b) but squared term missed here, no further marks.

1

= 0.3(01) Allow 0.299−0.304 Ignore units.

1

(d) M1 Decrease If M1 is incorrect CE=0 for the clip. If M1 is blank, mark on and seek to credit the correct information in the explanation.

1

M2 More moles on LHS / reactants or fewer / less moles on RHS / products (allow correct ratio 3:2)

M2 not just a generic statement ‘shifts to more moles’. 1

M3 (Equilibrium) shifts / moves either to oppose reduction in pressure / or to increase the pressure

M3 depends on a correct statement for M2. Not ‘favours’. Allow ‘to oppose change’ only if reduction in pressure noted.

1

(e) M1 T1

If M1 is incorrect, CE=0 for the clip. If M1 is blank, mark on and seek to credit the correct information in the explanation.

1

M2 (Forward*) reaction is exothermic OR Backward reaction is endothermic

*Assume answer refers to forward reaction unless otherwise stated.

1

M3 (at T2 or lower temperature)

(Equilibrium) shifted / moved to oppose reduction in temp

OR

at T1 or higher temp, (Equilibrium) shifted / moved to oppose (increase in temp)

M3 depends on a correct statement for M2

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Allow “to oppose change” only if change in temperature is stated. Not ‘favours’.

1 [12]

Q13. C

[1]

Q14.

(a) Kc = Penalise ( ) in this part but can score units; mark on in (b) If Kc expression wrong no marks in this part but can score M1 & M3 in (b)

1

units = mol−1 dm3

1

(b) [O2] = or or Correct answer scores three marks Ignore ( ) in this part Penalise contradiction in M1

M1 1

0.061(4) If Kc expression wrong in (a) can score M1 here for rearrangement of their Kc & M3 for multiplication by 1.4

M2

mol O2 = 0.0614 × 1.4 = 0.086 (allow 0.085−0.087) If Kc or rearrangement wrong here score only M3 for multiplication by 1.4

1

M3 = correct answer of (M2 × 1.4)

M3 1

(c) (i) No effect OR none OR no change OR stays the same 1

(ii) Effect: Increase or more SO3

Increase or more SO3

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If wrong effect, no further marks, but M2 and M3 are independent of each other

M1 1

Fewer mole(cule)s on RHS or 3 moles to 2 moles or (eqm shifts) to side with fewer moles (V3 or) residual V decreases in numerator of Kc expression

M2 1

Equilibrium moves / shifts to reduce the pressure / oppose the increase in pressure

to keep Kc constant,

ratio

must increase Allow to oppose the change only if increase pressure mentioned

M3 1

[9]

Q15. (a) (i) M1

High (temperature) OR Increase (the temperature) If M1 is incorrect CE = 0 for the clip If M1 is blank, mark on and seek to credit the correct information in the text

M2 The (forward) reaction / to the right is endothermic or takes in / absorbs heat OR The reverse reaction / to the left is exothermic or gives out / releases heat

M3 depends on correct M2 and must refer to temperature / heat M3 depends on a correct statement for M2

At high temperature, the (position of ) equilibrium shifts / moves left to right to oppose the increase in temperature

For M3, the position of equilibrium shifts / moves to absorb heat OR to lower the temperature OR to cool down the reaction

3

(ii) M1

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The reaction gets to equilibrium faster / in less time OR Produces a small yield faster / in less time OR Increases the rate (of reaction / of attainment of equilibrium)

Mark independently

M2

High pressure leads to one of the following • more particles / molecules in a given volume • particles / they are closer together • higher concentration of particles / molecules AND • more collisions in a given time / increased collision frequency

Penalise M2 for reference to increased energy of the particles 2

(iii) M1 Increase in / more / large(r) / big(ger) surface area / surface sites Mark independently For M1 accept Éan increase in surface”

M2 increase in / more successful / productive / effective collisions (in a given time) (on the surface of the catalyst / with the nickel)

For M2 not simply “more collisions” Ignore “the chance or likelihood” of collisions

2

(b) M1 No effect / None

If M1 is incorrect CE = 0 for the clip If M1 is blank, mark on and seek to credit the correct information in the text

M2 requires a correct M1 Equal / same number / amount of moles / molecules / particles on either side of the equation OR 2 moles / molecules / particles on the left and 2 moles / molecules / particles on the right

M2 depends on a correct statement for M1 In M2 not “atoms”

2 [9]

Q16. C

[1]

Q17. (a) Reheat the sample at least once.

Heat to constant mass gains both marks. 1

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Mass of ash should not have changed. Mark independently.

1

(b) Vacuum filtration is quicker / saves time Allow ‘easier to wash residue to extract all iodide ions’.

1

(c) Use indicator (paper) on a withdrawn sample / place a pH probe into the solution If any indicator (including paper) is used directly on the solution lose this mark but then mark on.

1

Keep testing until paper shows acidity / until pH drops below 7. Indicator does not need to be specified but if it is then correct colour must be quoted.

1

(d) 2I– + H2O2 + 2H+ → I2 + 2H2O Do not accept 2l– + H2O2 → I2 + 2OH– as reaction conditions are acidic. Accept multiples and fractions. Ignore state symbols.

1

(e) Lower layer – as it will be the denser CCl4

Mark is for correct identification and correct reasoning. 1

(f) Iodine in seaweed = 56.4 × (3/100) = 1.692 g 1

Iodine left in aqueous layer = 1.692 – 1.673 = 0.0190 g 1

K = (1.673/(253.8 × 0.05)) / (0.0190/(253.8 × 0.05)) = 88.1 Neither 253.8 nor 0.05 have to appear in working since they cancel. Accept 88

1

(g) It would react with the iodine Allow (electrophilic) addition OR forms 1,2 –diiodocyclohexane OR addition across a double bond for both marks.

1

It is unsaturated 1

(h) Solubility (of the iodine in the solvent) is high when hot and low when cold 1

(Therefore, on cooling a solution,) a significant quantity of crystals appear 1

[14]

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Q18.

(a) Penalise missing brackets or use of (); allow correct molecular formulae in correct expression (and allow CH2CH2); ignore powers shown as 1

1

M2 mol−1 dm3

Units must be in simplest form on one line (or dm3 mol−1) Units are consequential on expression in M1 (mol−1 dm3 only scores if it is the units for the expression in M1)

1

(b) 10.5 (3sf) scores both marks; Correct value to 2sf (10) or 4sf or more (10.476...) scores 1 mark Volume not used is CE=0 If use incorrect expression for Kc in part (b) then no marks in part (b)

1

M2 10.5 (must be 3sf) If a value from the question is copied incorrectly into the expression, could still score M2 if then used correctly in calculation (AE -1) Ignore units

1 [4]

Q19. A

[1]

Q20. (a) Stage 1: Moles of acid at equilibrium

Moles of sodium hydroxide in each titration = (3.20 × 2.00 × 10–1) / 1000 = 6.40 × 10–4

Extended response 1

Sample = 10 cm3 so moles of acid in 250 cm3 of equilibrium mixture = 25 × 6.40 × 10–4 = 1.60 × 10–2

M2 can only be scored if = answer to M1 × 25 1

Stage 2: Moles of ester and water formed

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Moles of acid reacted = 8.00 × 10–2 – 1.60 × 10–2 = 6.40 × 10–2

= moles ester and water formed M3 is 8.00 × 10–2 – M2

1

Stage 3: Moles of ethanol at equilibrium

Moles of ethanol remaining = 1.20 × 10–1 – 6.40 × 10–2 = 5.60 × 10–2

M4 is 1.20 × 10–1 – M3 1

Stage 4: Calculation of equilibrium constant

Kc = [CH3COOCH2CH3] [H2O] / [CH3COOH] [CH3CH2OH] 1

= (6.40 × 10–2)2 / (1.60 × 10–2)(5.60 × 10–2)

= 4.5714 = 4.57 M6 is M32 / M2 × M4 Answer must be given to 3 significant figures

1

(b)

Rough 1 2 3



Titre / cm3 4.50 4.00 4.20 3.95

1

(c) Mean = 4.00 + 3.95 / 2 = 3.98 (cm3) Allow 3.975 (cm3)

1

Titres 1 and 3 are concordant Allow titre 2 is not concordant

1

(d) Thymol blue 1

(e) Percentage uncertainty: 0.15 / 3.98 × 100 = 3.77% Allow consequential marking on mean titre from 2.3

1

(f) Use a lower concentration of NaOH 1

So that a larger titre is required (reduces percentage uncertainty in titre) 1

[13]

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Q21.

(a) 1

(b) 0.06 1

0.32 1

0.52 1

(c) 1

= (11.44) = 11 (2 sf) 1

No units 1

(d) Increase 1

[8]

Q22. A

[1]

Q23. (a) Bonds broken = 2(C=O) + 3(H–H) = 2 × 743 + 3 × H–H

Bonds formed = 3(C–H) +(C–O) + 3(O–H) = 3 × 412 + 360 + 3 × 463 Both required

1

–49 = [2 × 743 + 3 × (H–H)] – [3 × 412 + 360 + 3 × 463]

3(H–H) = –49 – 2 × 743 + [3 × 412 + 360 + 3 × 463] = 1450 Both required

1

H–H = 483 (kJ mol–1) Allow 483.3(3)

1

(b) Mean bond enthalpies are not the same as the actual bond enthalpies in CO2 (and / or methanol and / or water)

1

(c) The carbon dioxide (produced on burning methanol) is used up in this reaction 1

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(d) 4 mol of gas form 2 mol 1

At high pressure the position of equilibrium moves to the right to lower the pressure / oppose the high pressure

1

This increases the yield of methanol 1

(e) Impurities (or sulfur compounds) block the active sites Allow catalyst poisoned

1

(f) Stage 1: moles of components in the equilibrium mixture Extended response question

CO2(g) + 3H2(g) CH3OH(g) + H2O(g)

Initial moles 1.0 3.0 0 0

Eqm moles

(1–0.86) = 0.14

(3–3×0.86) = 0.42 0.86 0.86

1

Stage 2: Partial pressure calculations

Total moles of gas = 2.28

Partial pressures = mol fraction × ptotal 1

pCO2 = mol fraction × ptotal = 0.14 × 500 / 2.28 = 30.7 kPa

pH2 = mol fraction × ptotal = 0.42 × 500 / 2.28 = 92.1 kPa M3 is for partial pressures of both reactants Alternative M3 = ppCO2 = 0.0614 × 500 ppH2 = 0.1842 × 500

1

pCH3OH = mol fraction × ptotal = 0.86 × 500 / 2.28 = 188.6 kPa

pH2O = mol fraction × ptotal = 0.86 × 500 / 2.28 = 188.6 kPa M4 is for partial pressures of both products Alternative M4 = ppCH3OH = 0.3772 × 500 ppH2O = 0.3772 × 500

1

Stage 3: Equilibrium constant calculation Kp = pCH3OH × pH2O / pCO2 × (pH2)3

1

Hence Kp = 188.6 × 188.6 / 30.7 × (92.1)3 = 1.483 × 10–3 = 1.5 × 10–3

Answer must be to 2 significant figures

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1

Units = kPa–2

1 [16]

Q24. (a) Alkenes

1


1


1


(d) High pressure Allow pressure � MPa Mention of catalyst loses the mark

1


Level 3



5–6 marks

Level 2



3–4 marks

Level 1

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1–2 marks

Level 0


Indicative chemistry content Stage 1: consider effect of higher temperature on yield (Or vice versa for lower temperature) • Le Chatelier’s principle predicts that equilibrium shifts to oppose any increase in temperature • Exothermic reaction, so equilibrium shifts in endothermic direction / to the left • So a Higher T will reduce yield Stage 2: consider effect of higher temperature on rate (Or vice versa for lower temperature) • At higher temperature, more high energy molecules • more collisions have E>Ea • So rate of reaction increases / time to reach equilibrium decreases Stage 3: conclusion Industrial conditions chosen to achieve (cost-effective) balance of suitable yield at reasonable rate

[11]

Q25. (a) CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O

1

(b) 1

(c) A catalyst provides an alternative mechanism for reaction. 1

That has a lower activation energy. 1

(d) Kc expression shown correctly e.g. Kc = 1

Hence Kc = 4.07 = x2 / (0.0435 − x)2 (if x = amount of ester/water produced and therefore = amount by which amounts of acid and alcohol decreased).

1

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So So x = 0.0291 mol.

1

Acid left at equilibrium = 0.0435 − 0.0291 = 0.0144 mol. 1

Adding acid catalyst = 0.0144 + 2(0.0005) = 0.0154 mol (adding 2 × 0.0005 as 0.0005 mol of H2SO4 added and catalyst so not used up and dibasic).

1

Volume of alkali needed = 1000 × 0.0154/0.400 = 38.5 cm3. 1

(e) Test several samples − at least one tested after a week. 1

Check that the result has not changed. 1

[12]

Q26. (a) amount of X = 0.50 – 0.20 = 0.30 (mol)

1

amount of Y = 0.50 – 2 × 0.20 = 0.10 (mol) 1

(b) Axes labelled with values, units and scales that use over half of each axis All three of values, units and scales are required for the mark

1

Curve starts at origin 1

Then flattens at 30 seconds at 0.20 mol 1

(c) Expression = Kc = 1

[Y]2 = 1

[Y] = (0.35 / 0.40 × 2.9)0.5 = 0.5493 = 0.55 (mol dm–3) Answer must be to 2 significant figures

1

(d) Darkened / went more orange 1

The equilibrium moved to the right 1

To oppose the increased concentration of Y 1

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(e) The orange colour would fade 1

[12]



Level 3 (5 – 6 marks) All stages are covered and the explanation of each stage is generally correct and virtually complete. To access Level 3, statement 3a must be considered. Answer is communicated coherently and shows a logical progression from stage 1 (including 1b) to stage 2 and stage 3

Level 2 (3 – 4 marks) All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete. Answer is mainly coherent and shows progression from stage 1 to stage 2 and/or stage 3.

Level 1 (1 – 2 marks) Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete. Answer includes isolated statements but these are presented in a logical order, with sensible reasoning.

Level 0 (0 marks) Insufficient correct chemistry to gain a mark.

Indicative chemistry content

Stage 1 – Deductions from graph 1a Yield increases as temperature increases (or converse) 1b After a certain temperature yield no longer increases 1c Yield decreases as pressure increases (or converse)

Stage 2 – Optimum temperature and explanation 2a High temperature results in high energy costs/expensive 2b (After a certain temperature) yield no longer increases therefore there is no gain in using a higher temperature 2c Optimum temperature is between 780-880oC

Stage 3 – Optimum pressure and explanation 3a Low pressure may be too slow 3b So compromise pressure required 3c Optimum pressure is 1000-2000kPa or moderate pressure used

6

(b) Moles of carbon monoxide 17.9 Allow 17.94

1

Moles of hydrogen 19.9 Allow 19.88

1

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(c)

ignore brackets If Kp expression incorrect can only score M2 & M3 & M4

1

Total moles of gas = (2.76 + 4.51 + 0.36) = 7.63 If CE in M2 allow ecf for M3, M4 and M6 If no total moles calculated then can only score M1 and M6

1

pp(CO) = × 630 (kPa) (= 228 (kPa))

pp(H2) = × 630 (kPa) (= 372 (kPa))

pp(CH3OH) = × 630 (kPa) (= 29.7 (kPa))

All 3 pp of CO, H2 and CH3OH = 2 marks 2 pp correct = 1 mark

2

Kp = = 9.4(1) × 10−7 or 9.4(1) × 10−13 if pp in Pa

can also score M1 from this expression Allow 9.39 to 9.50 × 10−7 (kPa−2)

1

kPa−2 or Pa−2 (if converted to 630 000) If no marks awarded allow M6 only for kPa−2 or Pa−2

1 [14]

Q28. (a) Decrease

1

Increasing pressure moves equilibrium to the side of least moles i.e. backward reaction

1

To oppose the increase in pressure or to decrease the pressure 1

(b) A catalyst speeds up the rate of the forward and backward reaction 1

By the same amount 1

(c) ΔH = −111 − (−75 − 242) 1

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206 (kJ mol−1) 1

(d) ΔS = 3 × 131 + 198 − (186 + 189) = 216 J K−1 mol−1

1

ΔG = ΔH − TΔS 1

0 = 206 − T 1

T = 953.7 or 954 K 1

T = 681 (°C) If the value given in the question is used then the answer is 283 (°C)

1 [12]

Q29. (a) Mol CO = (0.73 − 0.43) = 0.30 (mol)

1

Mol H2 = (1.25 − 2(0.43)) = 0.39 (mol) 1

(b) Kc = 1

(c) Divides throughout by volume 1

Kc = 1

Kc =

Kc = 4.75 × 103

1

Unit = mol−2 dm+6

1

(d) pV = nRT

T = 1

n = 0.452 + 0.106 + 0.273 = 0.831 (mol) Calculation of moles and substitution of all values

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1

= Correct conversion of p and V

1

= 384 °C Conversion to °C

1 [11]

Q30. C

[1]

Q31. (a)

Allow CH3COOCH2CH2OOCCH3

OR CH3COOCH2CH2OCOCH3

OR

1

(b) Mol HOCH2CH2OH = 6.00 × 10−2 OR 0.06(00) 1

Mol C6H10O4 = 1.45 × 10−1 OR 0.145 1

Mol H2O = 2.90 × 10−1 OR 0.29(0) 1

(c)

Allow words for acid and alcohol

1

The volume cancels out (Penalise a contradictory justification from expression if the volumes do not cancel out) OR there are equal no of moles on each side of the equation OR

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there are equal no of molecules on each side of the equation 1

(d)

M1

M2

Mol CH3COOH = 0.789 (must be 3 sfs) Allow 0.788 – 0.790 M3

0.789 scores 3

Allow without V : (nCH3COOH)2 =

If (nCH3COOH)2 =0.623 then award M1 and M2

If Kc is correct in (c) but incorrect rearrangement, then CE=0 except if upside down rearrangement then M3 only awarded for 1.27

If Kc is incorrect in (c) then only M1 can be awarded for correct rearrangement.

[9]

Q32. D

[1]

Q33. D

[1]

Q34. (a) mol R = 2x

1

(b) 3.6 = M1 can be awarded for the insertion of their answer from (a) correctly

1

√3.6 = (only positive root to be used) M2 can be awarded if their expression is expanded

1

√3.6 −√3.6 x = 2x

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1.9 = 3.9x X = 0.49 [R] = 0.97 mol dm−3 (allow range 0.97–.098)

M3 solve for x from their expression in M1 and use it to calculate [R]

1 [4]

Q35. (a) (i) Curve drawn from origin with peak clearly lower and to right.

New curve crosses original once only, finishes above original and does not clearly curve up IGNORE relative areas

1

(ii) (Relative areas under curves indicate) many (owtte) more molecules with E greater than or equal to Ea (at higher T) or reverse argument

ALLOW ‘particles’ IGNORE ‘atoms’

1 (Large) increase in (number of) successful (owtte) collisions per unit time

OR ‘frequency of successful collisions’ 1

(b) (i) Yield increases Yield decreases/stays the same CE = 0 If not answered mark on

1 More moles/molecules (of gas) on left/fewer on right/3 on left 1 on right

1 Equilibrium shifts/moves (to right) to reduce pressure/oppose higher pressure

No M3 if ‘more moles on right’ in M2 IGNORE ‘favours’ NOT just ‘oppose the change’ QoL means that M3 is only awarded if these ideas are clearly linked in one statement

1

(ii) Higher T would increase rate but decrease yield/make less methanol OR Lower T decreases rate but increases yield;

If no mention of both rate AND (idea of) yield max 1 1

Chosen T is a compromise/balance (between rate and yield) owtte 1

[8]

Q36.

(i) In either order

M1 Concentration(s) (of reactants and products)

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remain(s) constant / stay(s) the same / remain(s) the same / do(es) not change

M2 Forward rate = Reverse / backward rate For M1 accept [ ] for concentration NOT “equal concentrations” and NOT “concentration(s) is/are the same” NOT “amount” Ignore “dynamic” and ignore “speed” Ignore “closed system” It is possible to score both marks under the heading of a single feature

2

(ii) M1

The (forward) reaction / to the right is endothermic or takes in / absorbs heat

OR

The reverse reaction / to the left is exothermic or gives out / releases heat

M2 depends on correct M1 and must refer to temperature/heat

The equilibrium shifts / moves left to right to oppose the increase in temperature M2 depends on a correct statement for M1 For M2, the equilibrium shifts/moves to absorb the heat OR to lower the temperature OR to cool the reaction

2

(iii) M1 refers to number of moles

There are fewer moles (of gas) on the left OR more moles (of gas) on the right. OR there is one mole (of gas) on the left and 2 moles on the right.

M2 depends on correct M1 and must refer to pressure The equilibrium shifts / moves right to left to oppose the increase in pressure

M2 depends on a correct statement for M1 For M2, the equilibrium shifts/moves to lower the pressure.

2 [6]

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Equilibrium and Kc exam pack 2

Name: ________________________

Class: ________________________

Date: ________________________

Time: 297 minutes

Marks: 293 marks

Comments:

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Q1. Nitrogen dioxide dissociates according to the following equation.

2NO2(g) 2NO(g) + O2(g)

When 21.3 g of nitrogen dioxide were heated to a constant temperature, T, in a flask of volume 11.5 dm3, an equilibrium mixture was formed which contained 7.04 g of oxygen.

(a) (i) Calculate the number of moles of oxygen present in this equilibrium mixture and deduce the number of moles of nitrogen monoxide also present in this equilibrium mixture.

Number of moles Of O2 at equilibrium ________________________________

______________________________________________________________

Number of moles of NO at equilibrium _______________________________

(ii) Calculate the number of moles in the original 21.3 g of nitrogen dioxide and hence calculate the number of moles of nitrogen dioxide present in this equilibrium mixture.

Original number of moles of NO2 ____________________________________

______________________________________________________________

Number of moles of NO2 at equilibrium _______________________________

______________________________________________________________ (4)

(b) Write an expression for the equilibrium constant, Kc, for this reaction. Calculate the value of this constant at temperature T and give its units.

Expression for Kc ____________________________________________________

___________________________________________________________________

Calculation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(c) The total number of moles of gas in the flask is 0.683. Use the ideal gas equation to determine the temperature T at which the total pressure in the flask is 3.30 × 105 Pa. (The gas constant R = 8.31 J K–1mol–1)

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(d) State the effect on the equilibrium yield of oxygen and on the value of Kc when the same mass of nitrogen dioxide is heated to the same temperature T, but in a different flask of greater volume.

Yield of oxygen ______________________________________________________

Value of Kc _________________________________________________________ (2)

(Total 13 marks)

Q2. The ester methyl ethanoate is hydrolysed as shown in the following equation.

CH3COOCH3(l) + H2O(l) CH3COOH(l) + CH3OH(l) ΔH = +3 kJ mol−1

A 3 mol sample of methyl ethanoate was mixed with 3 mol of water and left to reach equilibrium at 298 K. The equilibrium yield of ethanoic acid was 2 mol. The value of Kc for this reaction at 298 K is

A

B

C 2

D 4 (Total 1 mark)

Q3. Hydrogen is produced by the reaction between steam and methane when the following dynamic equilibrium is established.

CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH = +206 kJ mol–1

(a) Use Le Chatelier’s principle to predict the separate effects of an increase in temperature and of an increase in pressure on the yield of hydrogen obtained in the above reaction. In each case, explain your answer.

(6)

(b) State how, and explain why, the use of a catalyst might or might not change the equilibrium yield of hydrogen, and also the amount of hydrogen produced, in a given time.


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Q4. Methanol can be synthesised from carbon monoxide by the reversible reaction shown below.

CO(g) + 2H2(g) CH3OH(g) ΔH = –91 kJ mol–1

The process operates at a pressure of 5 MPa and a temperature of 700 K in the presence of a copper-containing catalyst. This reaction can reach dynamic equilibrium.

(a) By reference to rates and concentrations, explain the meaning of the term dynamic equilibrium.

___________________________________________________________________

___________________________________________________________________ (2)

(b) Explain why a high yield of methanol is favoured by high pressure.

___________________________________________________________________

___________________________________________________________________ (2)

(c) Suggest two reasons why the operation of this process at a pressure much higher than 5 MPa would be very expensive.

Reason 1 __________________________________________________________

Reason 2 __________________________________________________________

___________________________________________________________________ (2)

(d) State the effect of an increase in temperature on the equilibrium yield of methanol and explain your answer.

Effect _____________________________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(e) If a catalyst were not used in this process, the operating temperature would have to be greater than 700 K. Suggest why an increased temperature would be required.

___________________________________________________________________ (1)

(Total 10 marks)


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A saturated solution of magnesium hydroxide, Mg(OH)2, contains 0.1166 g of Mg(OH)2 in 10.00 dm3 of solution. In this solution the magnesium hydroxide is fully dissociated into ions.

The equilibrium constant expression for the dissolving of magnesium hydroxide is K = [Mg2+] [OH−]2. In a saturated solution of Mg(OH)2 at a different temperature, the concentration of hydroxide ions is 1.0 × 10−3 mol dm−3.

Which one of the following has the correct value and units for K under these conditions?

A 1.0 × 10−6 mol2 dm−6

B 5.0 × 10−7 mol2 dm−6

C 1.0 × 10−9 mol3 dm−9

D 5.0 × 10−10 mol3 dm−9

(Total 1 mark)

Q6. The ester methyl ethanoate is hydrolysed as shown in the following equation.

CH3COOCH3(l) + H2O(l) CH3COOH(l) + CH3OH(l) ΔH = +3 kJ mol−1

The equilibrium yield of ethanoic acid could be increased by

A lowering the temperature.

B adding a catalyst.

C adding more water to the reaction mixture.

D adding more methanol to the reaction mixture. (Total 1 mark)

Q7. (a) A flask containing a mixture of 0.200 mol of ethanoic acid and 0.110 mol of ethanol

was maintained at 25 °C until the following equilibrium had been established.

CH3COOH(l) + C2H5OH(l) CH3COOC2H5(l) + H2O(l)

The ethanoic acid present at equilibrium required 72.5 cm3 of a 1.50 mol dm–3 solution of sodium hydroxide for complete reaction.

(i) Calculate the value of the equilibrium constant, Kc, for this reaction at 25 °C.

(ii) The enthalpy change for this reaction is quite small. By reference to the number and type of bonds broken and made, explain how this might have been predicted.

(9)

(b) Aspirin can be prepared by acylation using either ethanoyl chloride or ethanoic anhydride, as represented by the equations shown below.

CH3COCl + HOC6H4COOH → CH3COOC6H4COOH + HCl

(CH3CO)2O + HOC6H4COOH → CH3COOC6H4COOH + CH3COOH

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(i) By a consideration of the intermolecular forces involved, explain why the product HCl is a gas but the product CH3COOH is a liquid at room temperature.

(ii) Give two industrial advantages of using ethanoic anhydride rather than ethanoyl chloride in the manufacture of aspirin.






The equilibrium yield in all three reactions is increased when

A the pressure is increased.

B the pressure is decreased.

C the temperature is increased.

D the temperature is decreased. (Total 1 mark)

Q9. Ethanoic acid reacts with ethanol in a reversible reaction represented by the equation below. In an experiment 3.0 mol of ethanoic acid were mixed with 1.0 mol of ethanol and when the reaction had reached equilibrium 0.9 mol of water had been formed.


The equilibrium constant for the reaction under these conditions is

A 0.20

B 0.23

C 3.9

C 4.3 (Total 1 mark)



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Possible units for the equilibrium constant, Kc, for reaction 2 are

A mol−2 m6

B mol−1 dm3

C no units

D mol dm−3

(Total 1 mark)

Q11. Hydrogen is produced on an industrial scale from methane as shown by the equation below.

CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH = +205 kJ mol–1

(a) State Le Chatelier’s principle.

___________________________________________________________________

___________________________________________________________________ (1)

(b) The following changes are made to this reaction at equilibrium. In each case, predict what would happen to the yield of hydrogen from a given amount of methane. Use Le Chatelier’s principle to explain your answer.

(i) The overall pressure is increased.

Effect on yield of hydrogen ________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

(ii) The concentration of steam in the reaction mixture is increased.

Effect on yield of hydrogen ________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________ (6)

(c) At equilibrium, a high yield of hydrogen is favoured by high temperature. In a typical industrial process, the operating temperature is usually less than 1200 K. Suggest two reasons why temperatures higher than this are not used.

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Reason 1 ___________________________________________________________

Reason 2 ___________________________________________________________

___________________________________________________________________ (2)

(Total 9 marks)

Q12. Ethanoic acid reacts with ethanol in a reversible reaction represented by the equation below. In an experiment 3.0 mol of ethanoic acid were mixed with 1.0 mol of ethanol and when the reaction had reached equilibrium 0.9 mol of water had been formed.


The percentage of ethanoic acid converted into the ester CH3COOC2H5 in this reaction is

A 22.5%

B 30%

C 43%

C 90% (Total 1 mark)

Q13. Methanol, CH3OH, is a convenient liquid fuel.

(a) An experiment was conducted to determine the enthalpy of combustion of liquid methanol. The energy obtained from burning 2.12 g of methanol was used to heat 150 g of water. The temperature of the water rose from 298 K to 362 K. (The specific heat capacity of water is 4.18 J K–1 g–1)


(ii) Use the data above to calculate a value for the enthalpy of combustion of one mole of liquid methanol.

(7)

(b) Methanol can be synthesised from methane and steam by a process that occurs in two stages.

Stage 1 CH4(g) + H2O(g) 3H2(g) + CO(g) ΔHO = +206 kJ mol–1

Stage 2 CO(g) + 2H2(g) CH3OH(g) ΔHO = –91 kJ mol–1

(i) Explain why, in Stage 1, a higher yield of hydrogen and carbon monoxide is not obtained if the pressure is increased.

(ii) Stage 2 is carried out at a compromise temperature of 500K. By considering what would happen at higher and lower temperatures, explain why 500 K is considered to be a compromise for Stage 2.

(5)

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(c) The standard enthalpies of combustion of carbon monoxide and of hydrogen are –283 kJ mol–1 and –286 kJ mol–1, respectively. Use these data and the enthalpy change for Stage 2 to calculate a value for the standard enthalpy of combustion of gaseous methanol.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 15 marks)

Q14. (a) The expression for an equilibrium constant, Kc, for a homogeneous equilibrium

reaction is given below.

(i) Write an equation for the forward reaction.

______________________________________________________________

(ii) Deduce the units of Kc

______________________________________________________________

(iii) State what can be deduced from the fact that the value of Kc is larger when the equilibrium is established at a lower temperature.

______________________________________________________________ (3)

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(b) A 36.8 g sample of N2O4 was heated in a closed flask of volume 16.0 dm3. An equilibrium was established at a constant temperature according to the following equation.

N2O4(g) 2NO2(g)

The equilibrium mixture was found to contain 0.180 mol of N2O4

(i) Calculate the number of moles of N2O4 in the 36.8 g sample.

______________________________________________________________

______________________________________________________________

(ii) Calculate the number of moles of NO2 in the equilibrium mixture.

______________________________________________________________

______________________________________________________________

(iii) Write an expression for Kc and calculate its value under these conditions.

Expression for Kc ________________________________________________

______________________________________________________________

Calculation _____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(iv) Another 36.8 g sample of N2O4 was heated to the same temperature as in the original experiment, but in a larger flask. State the effect, if any, of this change on the position of equilibrium and on the value of Kc compared with the original experiment.

Effect on the position of equilibrium _________________________________

Effect on the value of Kc __________________________________________ (9)

(Total 12 marks)

Q15. Methanol can be formed on an industrial scale from carbon dioxide and hydrogen by a reversible reaction as shown below.

CO2(g) + 3H2(g) CH3OH(g) + H2O(g)

The reaction can be carried out in the presence of a chromium-based catalyst at a temperature of 700 K and a pressure of 30 MPa. Under these conditions, equilibrium is reached when 2% of the carbon dioxide has been converted.

(a) How does the rate of the forward reaction compare with that of the backward reaction when 2% of the carbon dioxide has been converted?

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___________________________________________________________________ (1)

(b) (i) If the pressure was reduced but the temperature was kept the same, deduce what would happen to the equilibrium yield of methanol. Explain your answer.

Yield __________________________________________________________

Explanation ____________________________________________________

(ii) Give two reasons why, in general, industry prefers to operate processes at pressures lower than 30 MPa.

Reason 1 ______________________________________________________

Reason 2 ______________________________________________________ (5)

(c) If the chromium-based catalyst was replaced with a more efficient catalyst but other conditions were kept the same, deduce what would happen to the equilibrium yield of methanol. Explain your answer.

Yield ______________________________________________________________

Explanation _________________________________________________________ (2)

(d) In the presence of a very efficient copper-based catalyst, this industrial process can be operated at a lower temperature of 500 K and a pressure of 30 MPa. Under these conditions, at equilibrium, more of the carbon dioxide is converted into methanol.

Use this information to deduce the sign of the enthalpy change for the reaction. Explain your deduction.

Sign of enthalpy change _______________________________________________

Explanation _________________________________________________________ (3)

(e) In the processes above, the equilibrium yield of methanol is low. Suggest what is done with the unreacted carbon dioxide and hydrogen.

___________________________________________________________________ (1)

(Total 12 marks)

Q16. Tetrafluoroethene, C2F4, is obtained from chlorodifluoromethane, CHClF2, according to the equation:

2CHClF2(g) C2F4(g) + 2HCl(g) ΔHο = +128kJ mol–1

(a) A 1.0 mol sample of CHClF2 is placed in a container of volume 18.5 dm3 and heated.

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When equilibrium is reached, the mixture contains 0.20 mol of CHClF2

(i) Calculate the number of moles of C2F4 and the number of moles of HCl present at equilibrium.

Number of moles of C2F4 _________________________________________

Number of moles of HCl __________________________________________


______________________________________________________________

(iii) Calculate a value for Kc and give its units.

Calculation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Units _________________________________________________________ (6)

(b) (i) State how the temperature should be changed at constant pressure to increase the equilibrium yield of C2F4

______________________________________________________________

(ii) State how the total pressure should be changed at constant temperature to increase the equilibrium yield of C2F4

______________________________________________________________ (2)

(c) C2F4 is used to manufacture the polymer polytetrafluoroethene, PTFE. Name the type of polymerisation involved in the formation of PTFE.

___________________________________________________________________ (1)

(Total 9 marks)

Q17. (a) State and explain the effect of a catalyst on the rate and on the equilibrium yield in a

reversible reaction. (5)

(b) Explain the terms heterogeneous and active sites as applied to a catalyst. Give two reasons why a ceramic support is used for the catalyst in catalytic converters in cars.

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Explain how lead poisons this catalyst. (7)

(c) In aqueous solution, Fe2+ ions act as a homogeneous catalyst in the reaction between

I– and ions. Give one reason why the reaction is slow in the absence of a catalyst. Write equations to show how Fe2+ ions act as a catalyst for this reaction.


Q18. The standard enthalpy of formation, ΔHf for O3(g) is + 142 kJ mol–1. In which one of the following would both the changes shown increase the amount of O2 gas in an equilibrium mixture containing only O2(g) and O3(g)?

A increasing the temperature and increasing the pressure

B increasing the temperature and decreasing the pressure

C decreasing the temperature and increasing the pressure

D decreasing the temperature and decreasing the pressure (Total 1 mark)

Q20. (a) In an experiment, at a fixed temperature, an equilibrium mixture contained the

following amounts, in moles, of each component.

CH3CH2COOH CH3CH2OH CH3CH2COOCH2CH3 H2O

0.0424 0.0525 0.0745 0.0813

Use the data in the table above to calculate a value for the equilibrium constant, Kc, at this fixed temperature. Record your answer to the appropriate precision.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(b) If the mixture is uncovered during the time it is left to reach equilibrium, some of the ester formed will evaporate. Explain why a smaller volume of sodium hydroxide would then be required in the titration compared with the volume for the covered mixture.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

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(Total 4 marks)

Q21. In the Haber Process for the manufacture of ammonia, nitrogen and hydrogen react as shown in the equation.

N2(g) + 3H2(g) 2NH3(g) ∆Hο = –92 kJ mol–1

The table shows the percentage yield of ammonia, under different conditions of pressure and temperature, when the reaction has reached dynamic equilibrium.

Temperature / K 600 800 1000

% yield of ammonia at 10 MPa 50 10 2



(a) Explain the meaning of the term dynamic equilibrium.

___________________________________________________________________

___________________________________________________________________ (2)

(b) Use Le Chatelier’s principle to explain why, at a given temperature, the percentage yield of ammonia increases with an increase in overall pressure.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) Give a reason why a high pressure of 50 MPa is not normally used in the Haber Process.

___________________________________________________________________ (1)

(d) Many industrial ammonia plants operate at a compromise temperature of about 800 K.

(i) State and explain, by using Le Chatelier’s principle, one advantage, other than cost, of using a temperature lower than 800 K.

Advantage ____________________________________________________

Explanation ____________________________________________________

______________________________________________________________

(ii) State the major advantage of using a temperature higher than 800 K.

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______________________________________________________________

(iii) Hence explain why 800 K is referred to as a compromise temperature.

______________________________________________________________ (5)

(Total 11 marks)

Q22. At high temperatures, nitrogen is oxidised by oxygen to form nitrogen monoxide in a reversible reaction as shown in the equation below.

N2(g) + O2(g) 2NO(g) ∆Hο = +180 kJ mol–1

(a) In terms of electrons, give the meaning of the term oxidation.

___________________________________________________________________ (1)

(b) State and explain the effect of an increase in pressure, and the effect of an increase in temperature, on the yield of nitrogen monoxide in the above equilibrium.

Effect of an increase in pressure on the yield _______________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Effect of an increase in temperature on the yield ____________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (6)

(c) Nitrogen monoxide, NO, is formed when silver metal reduces nitrate ions, NO in acid solution.

(i) Deduce the oxidation state of nitrogen in NO and in NO

NO __________________________________________________________

NO _________________________________________________________

(ii) Write a half-equation for the reduction of NO ions in acid solution to form nitrogen monoxide and water.

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______________________________________________________________

(iii) Write a half-equation for the oxidation of silver metal to Ag+(aq) ions.

______________________________________________________________

(iv) Hence, deduce an overall equation for the reaction between silver metal and nitrate ions in acid solution.

______________________________________________________________ (5)

(Total 12 marks)

Q23. (a) The diagram below shows the effect of temperature and pressure on the equilibrium

yield of the product in a gaseous equilibrium.

(i) Use the diagram to deduce whether the forward reaction involves an increase or a decrease in the number of moles of gas. Explain your answer.

Change in number of moles _______________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________

(ii) Use the diagram to deduce whether the forward reaction is exothermic or endothermic. Explain your answer.

The forward reaction is ___________________________________________

Explanation ____________________________________________________

______________________________________________________________

______________________________________________________________ (6)

(b) When a 0.218 mol sample of hydrogen iodide was heated in a flask of volume V dm3, the following equilibrium was established at 700 K.

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2HI(g) H2(g) + I2(g)

The equilibrium mixture was found to contain 0.023 mol of hydrogen.

(i) Calculate the number of moles of iodine and the number of moles of hydrogen iodide in the equilibrium mixture.

Number of moles of iodine _________________________________________

Number of moles of hydrogen iodide _________________________________

______________________________________________________________


______________________________________________________________

______________________________________________________________

(iii) State why the volume of the flask need not be known when calculating a value for Kc.

______________________________________________________________

______________________________________________________________

(iv) Calculate the value of Kc at 700 K.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(v) Calculate the value of Kc at 700 K for the equilibrium

H2(g) + I2(g) 2HI(g)

______________________________________________________________

______________________________________________________________ (7)

(Total 13 marks)

Q24. The study of equilibrium constants enables chemists to calculate the composition of equilibrium mixtures.

(a) The expression for an equilibrium constant, Kc, for a homogeneous equilibrium is given below.

Kc =

(i) Write an equation for the forward reaction.

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______________________________________________________________

(ii) Deduce the units of Kc

______________________________________________________________

______________________________________________________________

(iii) State what can be deduced from the fact that the value of Kc is larger when the equilibrium is established at a lower temperature.

______________________________________________________________ (3)

(b) When a 0.218 mol sample of hydrogen iodide was heated in a flask of volume V dm3, the following equilibrium was established at 700 K.

2HI(g) H2(g) + I2(g)

The equilibrium mixture was found to contain 0.023 mol of hydrogen.

(i) Calculate the number of moles of iodine and the number of moles of hydrogen iodide in the equilibrium mixture.

Number of moles of iodine ________________________________________

Number of moles of hydrogen iodide ________________________________

______________________________________________________________


______________________________________________________________

______________________________________________________________

(iii) State why the volume of the flask need not be known when calculating a value for Kc.

______________________________________________________________

______________________________________________________________

(iv) Calculate the value of Kc at 700 K.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(v) Calculate the value of Kc at 700 K for the equilibrium

H2(g) + I2(g) 2HI(g)

______________________________________________________________

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______________________________________________________________ (7)

(Total 10 marks)

Q25. Methanol is a useful liquid fuel that can be produced by direct combination of carbon monoxide and hydrogen.

CO(g) + 2H2(g) CH3OH(g) ΔHο = –91 kJ mol–1

(a) Explain why a low temperature and a high pressure favour a high yield of methanol in this reaction.

Low temperature _____________________________________________________

___________________________________________________________________

___________________________________________________________________

High pressure _______________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(b) The industrial manufacture of methanol using this reaction is carried out at a compromise temperature of 400 °C under a pressure of 20 MPa in the presence of a Cr2O3/ZnO catalyst.

(i) Justify the use of a compromise temperature.

______________________________________________________________

______________________________________________________________

(ii) What effect, other than on the yield, does the use of high pressure have on the reaction?

______________________________________________________________ (3)

(Total 7 marks)

Q26. Carbon monoxide and hydrogen are used in the manufacture of methanol. An equilibrium is established according to the following equation.

Cu catalyst CO(g) + 2H2(g) CH3OH(g) ∆H = –9l kJ mol–1


Feature 1 ___________________________________________________________

___________________________________________________________________

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Feature 2 ___________________________________________________________

___________________________________________________________________ (2)

(b) Explain why an increase in temperature causes a decrease in the equilibrium yield of methanol.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(c) (i) State what is meant by the term catalyst.

______________________________________________________________

______________________________________________________________ (1)

(ii) State the effect, if any, of the copper catalyst on the position of this equilibrium at a fixed temperature.

______________________________________________________________ (1)

(d) Two methods are used to produce carbon monoxide from natural gas. Equations for these two methods are shown below.

Method 1 CH4 + H2O → 2CO + 3H2

Method 2 CH4 + CO2 → 2CO + 2H2

The manufacture of methanol from these sources of carbon monoxide has been described as carbon neutral.

(i) State what is meant by the term carbon neutral.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(ii) Show how combining the equations from these two methods can lead to the 1:2 mol ratio of carbon monoxide to hydrogen required for this synthesis of methanol.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(Total 8 marks)

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Q27. A mixture was prepared using 1.00 mol of propanoic acid, 2.00 mol of ethanol and 5.00 mol of water. At a given temperature, the mixture was left to reach equilibrium according to the following equation.

CH3CH2COOH + CH3CH2OH CH3CH2COOCH2CH3 + H2O ∆Hο = –22 kJ mol–1

The equilibrium mixture contained 0.54 mol of the ester ethyl propanoate.

(a) (i) Calculate the amounts, in moles, of propanoic acid, of ethanol and of water in this equilibrium mixture.

Moles of propanoic acid __________________________________________

Moles of ethanol ________________________________________________

Moles of water _________________________________________________ (3)

(ii) Write an expression for the equilibrium constant, Kc, for this equilibrium.

______________________________________________________________

______________________________________________________________ (1)

(iii) Calculate a value for Kc for this equilibrium at this temperature. Explain why this Kc value has no units.

Calculation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Explanation ____________________________________________________

______________________________________________________________ (3)

(b) For this equilibrium, predict the effect of an increase in temperature on each of the following.

(i) the amount, in moles, of ester at equilibrium

______________________________________________________________ (1)

(ii) the time taken to reach equilibrium

______________________________________________________________ (1)

(iii) the value of Kc

______________________________________________________________

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Q28. Synthesis gas is a mixture of carbon monoxide and hydrogen. Methanol can be manufactured from synthesis gas in a reversible reaction as shown by the following equation.

CO(g) + 2H2(g) CH3OH(g) ΔHο = –91 kJ mol–1

(a) A sample of synthesis gas containing 0.240 mol of carbon monoxide and 0.380 mol of hydrogen was sealed together with a catalyst in a container of volume 1.50 dm3. When equilibrium was established at temperature T1 the equilibrium mixture contained 0.170 mol of carbon monoxide.

Calculate the amount, in moles, of methanol and the amount, in moles, of hydrogen in the equilibrium mixture.

Methanol __________________________________________________________

Hydrogen __________________________________________________________ (2)

(b) A different sample of synthesis gas was allowed to reach equilibrium in a similar container of volume 1.50 dm3 at temperature T1

At equilibrium, the mixture contained 0.210 mol of carbon monoxide, 0.275 mol of hydrogen and 0.0820 mol of methanol.

(i) Write an expression for the equilibrium constant Kc for this reaction.

______________________________________________________________

______________________________________________________________ (1)

(ii) Calculate a value for Kc for the reaction at temperature T1 and state its units.

Calculation _____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Units _________________________________________________________

______________________________________________________________ (4)

(iii) State the effect, if any, on the value of Kc of adding more hydrogen to the equilibrium mixture.

______________________________________________________________

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(1)

(c) The temperature of the mixture in part (b) was changed to T2 and the mixture was left to reach a new equilibrium position. At this new temperature the equilibrium concentration of methanol had increased.

Deduce which of T1 or T2 is the higher temperature and explain your answer.


Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(d) The following reaction has been suggested as an alternative method for the production of methanol.

CO2(g) + 3H2(g) CH3OH(g) + H2O(g)

The hydrogen used in this method is obtained from the electrolysis of water.

Suggest one possible environmental disadvantage of the production of hydrogen by electrolysis.

___________________________________________________________________

___________________________________________________________________ (1)

(e) One industrial use of methanol is in the production of biodiesel from vegetable oils such as

Give the formula of one compound in biodiesel that is formed by the reaction of methanol with the vegetable oil shown above.

___________________________________________________________________ (1)

(Total 13 marks)

Q29. In the past 150 years, three different processes have been used to extract bromine from potassium bromide. These processes are illustrated below.

Extraction Process 1

2KBr + MnO2 + 2H2SO4 → MnSO4 + K2SO4 + 2H2O + Br2


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The reaction of solid potassium bromide with concentrated sulfuric acid.


The reaction of aqueous potassium bromide with chlorine gas.

(a) Write a half-equation for the conversion of MnO2 in acid solution into Mn2+ ions and water. In terms of electrons, state what is meant by the term oxidising agent and identify the oxidising agent in the overall reaction.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(b) Write an equation for Extraction Process 2 and an equation for Extraction Process 3. Calculate the percentage atom economy for the extraction of bromine from potassium bromide by Extraction Process 3. Suggest why Extraction Process 3 is the method in large-scale use today.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (5)

(c) Bromine has been used for more than 70 years to treat the water in swimming pools. The following equilibrium is established when bromine is added to water.

Br2 + H2O HBrO + HBr

Give the oxidation state of bromine in HBr and in HBrO

Deduce what will happen to this equilibrium as the HBrO reacts with micro-organisms in the swimming pool water. Explain your answer.

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___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (4)

(Total 12 marks)

Q30. Hydrogen gas is used in the chemical industry.

(a) Tungsten is extracted by passing hydrogen over heated tungsten oxide (WO3).

(i) State the role of the hydrogen in this reaction.

______________________________________________________________ (1)

(ii) Write an equation for this reaction.

______________________________________________________________ (1)

(iii) State one risk of using hydrogen gas in metal extractions.

______________________________________________________________

______________________________________________________________ (1)

(b) Hydrogen is used to convert oleic acid into stearic acid as shown by the following equation.

+ H2 CH3(CH2)16COOH

oleic acid stearic acid

(i) Use your knowledge of the chemistry of alkenes to deduce the type of reaction that has occurred in this conversion.

______________________________________________________________ (1)

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(ii) State the type of stereoisomerism shown by oleic acid.

______________________________________________________________ (1)

(c) Hydrogen reacts with nitrogen in the Haber Process. The equation for the equilibrium that is established is shown below.

N2(g) + 3H2(g) 2NH3(g)


______________________________________________________________

______________________________________________________________ (1)

(ii) Use Le Chatelier’s principle to explain why an increase in the total pressure of this equilibrium results in an increase in the equilibrium yield of ammonia.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________ (2)

(d) Hydrogen reacts with oxygen in an exothermic reaction as shown by the following equation.

H2(g) + O2(g) → H2O(g) ∆H = –242 kJ mol–1

Use the information in the equation and the data in the following table to calculate a value for the bond enthalpy of the H–H bond.

O–H O=O

Mean bond enthalpy / kJ mol–1 + 463 + 496

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(Total 11 marks)

Q31. The reaction of methane with steam produces hydrogen for use in many industrial

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processes. Under certain conditions the following reaction occurs.

CH4(g) + 2H2O(g) CO2(g) + 4H2(g) ∆Hο = +165 kJ mol–1

(a) Initially, 1.0 mol of methane and 2.0 mol of steam were placed in a flask and heated with a catalyst until equilibrium was established. The equilibrium mixture contained 0.25 mol of carbon dioxide.

(i) Calculate the amounts, in moles, of methane, steam and hydrogen in the equilibrium mixture.

Moles of methane _______________________________________________

Moles of steam _________________________________________________

Moles of hydrogen _______________________________________________ (3)

(ii) The volume of the flask was 5.0 dm3. Calculate the concentration, in mol dm–3, of methane in the equilibrium mixture.

______________________________________________________________

______________________________________________________________ (1)

(b) The table below shows the equilibrium concentration of each gas in a different equilibrium mixture in the same flask and at temperature T.

gas CH4(g) H2O(g) CO2(g) H2(g)

concentration / mol dm–3 0.10 0.48 0.15 0.25

(i) Write an expression for the equilibrium constant, Kc, for this reaction.

______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(ii) Calculate a value for Kc at temperature T and give its units.

Calculation ____________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

Units of Kc _____________________________________________________ (3)

(c) The mixture in part (b) was placed in a flask of volume greater than 5.0 dm3 and

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allowed to reach equilibrium at temperature T. State and explain the effect on the amount of hydrogen.

Effect on amount of hydrogen ___________________________________________

Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(d) Explain why the amount of hydrogen decreases when the mixture in part (b) reaches equilibrium at a lower temperature.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________ (2)

(Total 13 marks)

Q32. Sulfuric acid is made from SO3 which can be manufactured in a series of stages from iron(II) disulfide (FeS2), found in the mineral iron pyrites.

(a) In the first stage, FeS2 is roasted in air to form iron(III) oxide and sulfur dioxide.

(i) Balance the following equation for this reaction.

..........FeS2 + ..........O2 → ..........Fe2O3 + ..........SO2

(1)

(ii) Deduce the oxidation state of sulfur in each of the following compounds.

SO2 __________________________________________________________

FeS2 __________________________________________________________ (2)

(b) In the second stage of the manufacture of sulfuric acid, sulfur dioxide reacts with oxygen. The equation for the equilibrium that is established is shown below.

SO2(g) + O2(g) SO3(g) ΔH = –98 kJ mol–1

State and explain the effect of an increase in temperature on the equilibrium yield of SO3

Effect of increase in temperature on yield _________________________________

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Explanation _________________________________________________________

___________________________________________________________________

___________________________________________________________________ (3)

(c) In the extraction of iron, carbon monoxide reacts with iron(III) oxide. Write an equation for this reaction and state the role of the carbon monoxide.

Equation ___________________________________________________________

Role of the carbon monoxide ___________________________________________ (2)

(Total 8 marks)

Q33. (a) State why it is necessary to maintain a constant temperature in an experiment to

measure an equilibrium constant.

___________________________________________________________________ (1)

(b) Suggest one method for maintaining a constant temperature in an experiment.

___________________________________________________________________ (1)

(Total 2 marks)

Q34. The following dynamic equilibrium was established at temperature T in a closed container.

P(g) + 2Q(g) 2R(g) ΔHο = –50 kJ mol–1

The value of Kc for the reaction was 68.0 mol–1 dm3 when the equilibrium mixture contained 3.82 mol of P and 5.24 mol of R.

(a) Give the meaning of the term dynamic equilibrium.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (2)

(b) Write an expression for Kc for this reaction.

___________________________________________________________________

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___________________________________________________________________ (1)

(c) The volume of the container was 10.0 dm3.

Calculate the concentration, in mol dm–3, of Q in the equilibrium mixture.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(Extra space) ________________________________________________________

___________________________________________________________________ (4)

(d) State the effect, if any, on the equilibrium amount of P of increasing the temperature. All other factors are unchanged.

___________________________________________________________________ (1)

(e) State the effect, if any, on the equilibrium amount of P of using a container of larger volume. All other factors are unchanged.

___________________________________________________________________ (1)

(f) State the effect, if any, on the value of Kc of increasing the temperature. All other factors are unchanged.

___________________________________________________________________ (1)

(g) State the effect, if any, on the value of Kc of using a container of larger volume. All other factors are unchanged.

___________________________________________________________________ (1)

(h) Deduce the value of the equilibrium constant, at temperature T, for the reaction

2R(g) P(g) + 2Q(g)

___________________________________________________________________

___________________________________________________________________ (1)

(Total 12 marks)

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Q35. Oxygen and ozone (O3) both occur as gases in the upper atmosphere. Chlorine atoms catalyse the decomposition of ozone and contribute to the formation of a hole in the ozone layer. These chlorine atoms are formed from chlorofluorocarbons (CFCs) such as CF3Cl

(a) (i) Give the IUPAC name of CF3Cl

______________________________________________________________ (1)

(ii) Complete the following equation that shows the formation of a chlorine atom from a molecule of CF3Cl

(1)

(iii) State what the • represents in Cl•

______________________________________________________________ (1)

(b) Write two equations that show how chlorine atoms catalyse the decomposition of ozone into oxygen.

Equation 1 __________________________________________________________

Equation 2 __________________________________________________________ (2)

(c) An equilibrium is established between oxygen and ozone molecules as shown below.

3O2(g) 2O3(g) ΔH = +284 kJ mol–1


______________________________________________________________

______________________________________________________________

______________________________________________________________ (1)

(ii) Use Le Chatelier’s principle to explain how an increase in temperature causes an increase in the equilibrium yield of ozone.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

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(2)

(d) Chemists supported the legislation to ban the use of CFCs. Modern refrigerators use pentane rather than CFCs as refrigerants. With reference to its formula, state why pentane is a more environmentally acceptable refrigerant.

___________________________________________________________________

___________________________________________________________________ (1)

(Total 9 marks)

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Mark schemes

Q1.

(a) (i) Number of moles of O2 at equilibrium: = 0.22 (1)

Number of moles of NO at equilibrium: 0.44 (1) OR 2 × mol of oxygen

3

(ii) Original number of moles of NO2: = 0.46(3) (1)

Number of moles of NO2 at equilibrium: 0.46(3) – 0.44 = 0.02(3) (1)

OR conseq on mol NO above 1

(b) Expression for KC: KC = (1)

Calculation: KC = = 7.0(0) mol dm–3

(1) (1) (1) If mol NO2 = 0.02; KC = 9.26 (9.3) or conseq on values from (a) If vol missed, score only KC and units If KC wrong: max 2 for correct use of vol and conseq units If KC wrong and no vol: max 1 for conseq units

3

(c) pV = nRT (1)

T = =

(1) for using 11.5 × 10–3 as V

T = 669 K (1) 4

(d) Yield of oxygen: increased (1) Value of Kc: no effect (1)

2 [13]

Q2. D

[1]

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Q3. (a) Increase in temperature:

Yield is increased (Allow if for H2 (g) or products) (1) Reaction endothermic (1) Equilibrium moves to the right OR forward, OR Equilibrium moves to oppose change OR to absorb heat (1)

If “Yield statement” incorrect allow max one if reaction stated to be endothermic

Increase in pressure:

Yield is decreased (Allow if for H2 (g) or products) (1) Increase in moles of gas or 2 moles increased to 4 moles or more moles on right (1) Equilibrium moves to the left OR backwards, OR Equilibrium moves to oppose change OR to reduce pressure (1)

If “Yield statement” incorrect allow max one if number of moles change is correct.

6

(b) Equilibrium yield: Unaffected or equilibrium unchanged (1) Rate or speed increased (1) Forward and backwards reactions equally or by the same amount (1)

Amount of hydrogen produced: More hydrogen produced (1)

4 [10]

Q4. (a) rate forward reaction = rate backward reaction (1)

concentration remains constant (1) NOT ‘Equal’, Allow ‘The same’ if clear that means constant

2

(b) fewer moles (of gas) on R.H.S (1) (or converse) (methanol favoured) by reducing applied pressure (1)

Or removing constraint 2

(c) Power / energy required to provide high pressure / pumping (1) Strong pressure vessel / or equipment (1)

High maintenance costs (1) High insurance costs (1) Any two

2

(d) Effect: decreases (1) Explanation: reaction exothermic (or reverse reaction endothermic) (1) system tries to lower T or remove constraint or oppose the change or endothermic reaction favoured

3

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(e) to speed up reaction (1) or otherwise to slow or takes too long or to give more molecules E > EA

1 [10]

Q5. D

[1]

Q6. C

[1]

Q7. (a) (i) Moles NaOH = mv/1000 = 1.50 × 72.5/1000 = 0.108 to 0.11 (1)

Moles of ethanoic acid at equilibrium = moles sodium hydroxide (1) Moles ester = moles water (=moles acid reacted) (1) = 0.200 – 0.108 = 0.090 to 0.092 (1) Moles ethanol = 0.110 – 0.091 = 0.018 to 0.020 (1) KC = [Ester] [Water]/[Acid] [Alcohol] (1)

Allow if used correctly

= (0.091)2/0.109 × 0.019 = 3.7 to 4.9 (1) Ignore units NB Allow the answer 4 one mark as correct knowledge

7

(ii) Similar (types) of bond broken and made (1) Same number of the bonds broken and made (1)

any number if equal NB If a list given then the total number of each type of bond

broken and made must be the same 2

(b) (i) (Weak) dipole-dipole attraction between HCl molecules (1) (Strong) hydrogen bonds between CH3COOH molecules (1)

NB Ignore van der Waals forces 2

(ii) Ethanoic anhydride is

cheap compared to ethanoyl chloride (1)

less corrosive than ethanoyl chloride or HCl evolved (1)

reaction less violent or vigorous or exothermic or dangerous or safer to use (1)

less vulnerable to hydrolysis (1)

reaction more easily controlled (1) Max 2

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[13]

Q8. D

[1]

Q9. C

[1]

Q10. B

[1]

Q11. (a) An equilibrium opposes change (1)

1

(b) (i) Effect on yield of hydrogen: decreases (1) Note C.E. if not decrease, but mark on if no answer

Explanation: pressure lowered (or increase opposed) (1) by favouring fewer moles (of gas) (1)

(ii) Effect on yield of hydrogen: increase (1) CE if wrong as above

Explanation: pressure / concentration / reactants / steam reduced (1) by shifting to right (1)

or steam removed or forward reaction favoured 6

(c) Reason 1: cost of high temperature / energy (1)

Reason 2: cost of plant (to resist high T) too high (1) OR plant could not contain high T

2 [9]

Q12. B

[1]

Q13. (a) (i) enthalpy change when 1 mol of a substance

(or compound) (QL mark) 1

is (completely) burned in oxygen (or reacted in excess oxygen) 1

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at 298 K and 100 kPa (or under standard conditions) 1

(ii) heat produced = mass of water × Sp heat capacity xΔT (or mcΔT)

1

= 150 × 4.18 × 64 (note if mass = 2.12 lose first 2 marks then conseq) = 40100 J or = 40.1 kJ (allow 39.9 - 40.2 must have correct units)

1

moles methanol = mass/Mr = 2.12/32 (1) = 0.0663

1

ΔH = – 40.1/0.0663 = – 605 kJ (mol–1) 1

(allow –602 to –608 or answer in J) (note allow conseq marking after all mistakes but note use of 2.12 g loses 2 marks

(b) (i) equilibrium shifts to left at high pressure 1

because position of equilibrium moves to favour fewer moles (of gas)

1

(ii) at high temperature reaction yield is low (or at low T yield is high) 1

at low temperature reaction is slow (or at high T reaction is fast) 1

therefore use a balance (or compromise) between rate and yield 1

(c) ΔH = ΣΔHcο(reactants) – ΣΔHcο (products) (or correct cycle) 1

ΔHcο (CH3OH) = ΔHcο(CO) + 2 × ΔHcο(H2) – ΔH 1

= (–283) + (2 × –286) – (–91) (mark for previous equation or this) = –764 (kJ mol–1) ( units not essential but lose mark if units wrong) (note + 764 scores 1/3)

1 [15]

Q14. (a) (i) C + 3D 2A + B

1

(ii) mol dm–3

1

(iii) (forward reaction is) exothermic or more products formed 1

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(b) (i) for N2O4 Mr = 92.0 1

Mol = 1

(ii) mol N2O4 reacted = 0.400 – 0.180 = 0.220 1

mol NO2 formed = 0.440 1

(iii) Kc = (NO2)2

1 (N2O4)

= (0.44/16)2

1 (0.18/16)

= 0.067 1

(iv) move to NO2/ to right / forwards 1

none 1

[12]

Q15. (a) Same

1

(b) (i) Decreases 1

More moles on left hand side 1

Equilibrium moves to increase the pressure (Or to oppose the change or to compensate for low pressure)

1

(ii) Cost of producing high pressure (1) Cost of plant to resist high pressure (1) Correct safety factor with reason (1)

max 2

(c) No change 1

Catalyst has no effect on equilibrium position (Or catalyst affects rate of forward and backwards reactions equally)

1

(d) Negative

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1

Reaction (or equilibrium) moves in the exothermic direction (or to the right)

1

In order to oppose the change (or to raise the temperature) 1

(e) Recycled (or re-used or ‘put back in’) 1

[12]

Q16. (a) (i) moles of C2F2 = 0.40 mark independently from HC1

1

moles of HC1 = 0.80 not consequential 1

(ii)

wrong Kc means they can only

score for units in (iii) consequ

on their Kc 1

(iii) 1

= 0.35 1

mol dm–3

1

(b) (i) increase 1

(ii) decrease 1

(c) addition or radical 1

[9]

Q17. (a) effect on reaction rate: catalyst provides an alternative reaction route.;

1

with a lower Ea; 1

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more molecules able to react or rate increased; 1

equilibrium: forward and backward rates changes by the same amount;

1

hence concentration of reactants and products constant or yield unchanged;

1

(b) heterogeneous: catalyst in a different phase or state to that of the reactants;

1

active site: place where reactants adsorbed or attached or bond etc.; 1

reaction occurs or an explanation of what happens; (allow absorbed)

1

reasons: large surface area; reduce cost or amount of catalyst;

2

catalyst poison: lead adsorbed; lead not desorbed or site blocked;

(lead adsorbed irreversibly scores both of these marks) 2

(c) reaction slow as: both ions negatively charged or ions repel; 1

2Fe2+ + S2O82– → 2Fe3+ + 2SO42– Species; Balanced;

2

2Fe3+ +2I– → 2Fe2+ + I2 Species ; Balanced;

2 [17]

Q18. D

[1]

Q19. (a) mark labelled X on curve A where curve C joins A;

1

(b) equilibrium opposes a change; (Q of L mark)

1

(c) B 1

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more ammonia is produced (or yield increases); 1

fewer moles (of gas) on right ( or 4 mol goes to 2 mol); 1

equilibrium moves to oppose increase in pressure (or oppose change); 1

(d) C 1

amount of ammonia (or yield or equilibrium) unchanged; 1

reaction is faster; 1

[9]

Q20. (a) = (0.0745) × (0.0813) / (0.0424) × (0.0525)

= 2.72 Allow answer only without working if correct. Lose this mark if the wrong Kc expression is used.

1

Answer, whether or not correct, given to three significant figs Do not expect conversion from moles to concentration but allow if shown.

1

(b) Less acid is present (so less NaOH needed) 1

Equilibrium would shift to right (side with more ester / less acid) 1

[4]

Q21. (a) Rate forward reaction = rate backward reaction (1)

Concentrations of reactants and products are constant (1) 2

(b) System opposes change (1)

Moves to the side with fewer moles (1)

In this case NH3 (2 moles) on right side < N2 + H2 together (4 moles) on left side of equation (1)

3

(c) Too expensive to generate etc (1) 1

(d) (i) Yield of ammonia increases (1)

Exothermic reaction favoured (1)

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System moves to raise temp / or oppose decrease in temp (1) 3

(ii) Faster reaction (1) 1

(iii) Balance between rate and yield (1) 1

[11]

Q22. (a) removal/loss of electrons

1

(b) no change 1

equal number of gaseous moles on either side 1

both sides affected equally 1

increases 1

equilibrium moves to lower the temperature/oppose the change 1

endothermic reaction favoured /forward reaction is endothermic 1

(c) (i) +2 1

+5 1

(ii) NO3– + 4H+ + 3e– → NO +2H2O 1

(iii) Ag → Ag+ + e–

1

(iv) NO3– + 4H+ + 3Ag → NO + 2H2O + 3Ag+

1 [12]

Q23. (a) (i) Increase (if wrong no further marks in part (i)

1

higher P gives lower yield or moves to left 1

Eqm shifts to reduce P or eqm favours side with fewer moles 1

(ii) Endothermic if wrong no further marks in part (ii) 1

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increase T increases yield or moves to right 1

Eqm shifts to reduce T or eqm favours endothermic direction 1

(b) (i) Moles of iodine = 0.023 If wrong no marks in (i)

1

Moles of HI = 0.172 1

If × 2 missed, max 1 in part (iv)

(ii) Kc = must be square brackets (penalise once in paper) – if round, penalise but mark on in (iv) if Kc wrong, no marks in (iv) either but mark on from a minor slip in formula

1

(iii) V cancels in Kc expression or no moles same on top and bottom of expression or total moles reactants = moles products, i.e. total no of moles does not change

1

(iv) Kc = Conseq on (i)

1

= 0.0179 or 1.79 × 10–2

Allow 0.018 or 1.8 × 10–2

1

(v) Kc = 55.9 or 56 Conseq i.e. (answer to (iv))–1

1 [13]

Q24. (a) (i) C + 3D → 2A + B

1

(ii) mol dm–3

1

(iii) (forward reaction is) exothermic or more products formed 1

(b) (i) Moles of iodine = 0.023 1

Moles of HI = 0.172

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1

(ii) Kc = 1

(iii) V cancels in Kc expression 1

(iv) Kc = 1

= 0.0179 or 1.79 × 10–2

1

(v) Kc = 55.9 or 56 Conseq i.e. (answer to (iv))–1

1 [10]

Q25. (a) Low temperature

Reaction is exothermic 1

Low T reduces effect of heat evolved or heat evolved opposes the change in temperature

1 High pressure 3 mol gas → 1 mol gas

1 High p favours fewer moles by lowering p or forward reaction reduces volume and lowers p

1

(b) High T gives a low yield 1

but Low T gives a low rate compromise 1

increases reaction rate/catalyst surface contact 1

[7]

Q26. (a) M1 Concentrations of reactants and products remain constant

For M1 NOT “equal concentrations” NOT “amount”

1

M2 Forward rate = Reverse / backward rate Credit the use of [ ] for concentration Ignore dynamic, ignore closed system

1

(b) M1 The (forward) reaction / to the right is exothermic or

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releases heat OR converse for reverse reaction. 1

M2 The equilibrium responds by absorbing heat / lowering temperature OR Promotes the endothermic reaction by absorbing heat / lowering temperature OR Temperature increase is opposed (by shift to the left) OR Change is opposed by absorbing heat / lowering temperature.

1

(c) (i) A substance that speeds up / alters the rate but is unchanged at the end / not used up.

Both ideas needed Ignore references to activation energy and alternative route.

1

(ii) None OR no change OR no effect OR nothing OR Does not affect it / the position (of equilibrium) OR (The position is) the same or unchanged.

1

(d) (i) An activity which has no net / overall (annual) carbon emissions to the atmosphere OR An activity which has no net / overall (annual) greenhouse gas emissions to the atmosphere. OR There is no change in the total amount of carbon dioxide / carbon /greenhouse gas present in the atmosphere.

The idea that the carbon / CO2 given out equals the carbon / CO2 that was taken in Ignore carbon monoxide

1

(ii) A method which shows (see below) OR states in words that two times the first equation + the second equation gives the correct ratio.

2 (CH4 + H2O → CO + 3H2) CH4 + CO2 → 2CO + 2H2

3CH4 + 2H2O + CO2 → 4CO + 8H2

Ratio = 1 : 2 1

[8]

Q27. (a) (i) acid 0.46

1

alcohol 1.46 1

water 5.54 1

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(ii) Kc = penalise ( ) allow molecular formulae or minor slip in formulae

1

(iii) Allow without V Conseq on values in (a)(i) If values used wrongly or wrong values inserted or wrong Kc no marks for calc

1

4.45 or 4.5 Part (a)(iii) for info 0.46 × 1.46 = 0.6716

1

cancel (as equal no of moles on each side of equation) 1

Possible wrong answers

acid 0.46 gives

alcohol 1.46 Kc = 3.59

water 4.46

acid 0.46 gives

alcohol 1.46 Kc = 0.434

water 0.54

(b) (i) decrease or be reduced or fewer 1

(ii) decrease or be reduced or less time or faster or quicker 1

(iii) decrease or be reduced 1

[10]

Q28. (a) mol CH3OH = 0.07(0)

1

mol H2 = 0.24(0) 1

(b) (i)

of 57

or allow ( ) but expression using formulae must have brackets alternative expression using numbers must include volumes

1

(ii) M1 divides by vol Mark independently from (b)(i) any AE is –1 if volume missed, can score only M3 and M4

1

M2 mark is for correct insertion of correct numbers in correct Kc expression in b(ii) If Kc expression wrong, can only score M1 & M4 If numbers rounded, allow M2 but check range for M3

1

M3 11.6 or 11.7 mark for answer above 11.7 up to 12.2 scores 2 for M1 and M2 if vol missed, can score M3 for 5.16 (allow range 4.88 to 5.21)

1

M4 mol–2 dm6

Units conseq to their Kc in (b)(ii) 1

(iii) no effect or no change or none 1

(c) M1 T1

if wrong - no further marks 1

M2 (forward) reaction is exothermic OR gives out heat

backward reaction is endothermic only award M3 if M2 is correct

1

M3 shifts to RHS to replace lost heat

OR to increase the temperature

OR to oppose fall in temp

backward reaction takes in heat

OR to lower the temperature not just to oppose the change

1

(d) fossil fuels used

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OR CO2 H2O produced/given off/formed which are greenhouse gases OR SO2 produced/given off/formed which causes acid rain OR Carbon produced/given off/formed causes global dimming

not allow electricity is expensive ignore just global warming ignore energy or hazard discussion

1

(e) C17H35COOCH3 or C17H31COOCH3 or C17H29COOCH3

OR

CH3OOCC17H35 or CH3OOCC17H31 or CH3OOCC17H29 1

[13]

Q29. (a) M1 MnO2 + 4H+ + 2e– → Mn2+ + 2H2O

1

OR multiples

M2 An oxidising agent is an electron acceptor OR receives / accepts / gains electrons

Ignore state symbols M2 NOT an “electron pair acceptor”

1

M3 MnO2 is the oxidising agent Ignore “takes electrons” or “takes away electrons”

1

(b) M1 Formation of SO2 and Br2 (could be in an equation) 1

M2 Balanced equation Several possible equations 2KBr + 3H2SO4 → 2KHSO4 + Br2 + SO2 + 2H2O OR 2KBr + 2H2SO4 → K2SO4 + Br2 + SO2 + 2H2O

1

M3 2KBr + Cl2 → 2KCl + Br2

M2 Could be ionic equation with or without K+

2Br– + 6H+ + 3SO42– → Br2 + 2HSO4– + SO2 + 2H2O (3H2SO4) 2Br– + 4H+ + SO42– → Br2 + SO2 + 2H2O (2HBr + H2SO4) Accept HBr and H2SO4 in these equations as shown or mixed variants that balance. Ignore equations for KBr reacting to produce HBr M3 Could be ionic equation with or without K+

2Br– + Cl2 → 2Cl– + Br2 1

of 57

M4 % atom economy of bromine

=

= 51.7% OR 52% M4 Ignore greater number of significant figures

1

M5 One from:

• High atom economy

• Less waste products

• Cl2 is available on a large-scale

• No SO2 produced

• Does not use concentrated H2SO4

• (Aqueous) KBr or bromide (ion) in seawater.

• Process 3 is simple(st) or easiest to carry out M5 Ignore reference to cost Ignore reference to yield

1

(c) M1 HBr –1 1

M2 HBrO (+)1 1

M3 Equilibrium will shift to the right OR L to R OR Favours forward reaction OR Produces more HBrO

1

M4 Consequential on correct M3 OR to oppose the loss of HBrO OR replaces (or implied) the HBrO (that has been used up)

1 [12]

Q30. (a) (i) Reducing agent

OR

Reduce(s) (WO3/tungsten oxide)

of 57

OR

electron donor

OR

to remove oxygen (from WO3/tungsten oxide or to form water); 1

(ii) WO3 + 3H2 → W + 3H2O Or multiples

1

(iii) One from

H2 is

• explosive

• flammable or inflammable

• easily ignited Ignore reference to pressure or temperature

1

(b) (i) Addition Ignore “electrophilic” Penalise “nucleophilic addition”

OR

(catalytic) hydrogenation

OR

Reduction 1

(ii) Geometric(al)

OR

cis/trans OR E Z OR E/Z 1

(c) (i) (If any factor is changed which affects an equilibrium), the position of equilibrium will shift/move/change/respond/act so as to oppose the change.

OR


A variety of wording will be seen here and the key part is the last phrase and must refer to movement of the equilibrium. QoL

1

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(ii) M1 – Statement of number of moles/molecules There are more moles/molecules (of gas) on the left/of reactants

OR

fewer moles/molecules (of gas) on the right./products

OR

there are 4 moles/molecules (of gas) on the left and 2 moles/ molecules on the right.

Ignore “volumes” for M1 Mark independently

M2 – Explanation of response/movement in terms of pressure Increase in pressure is opposed (or words to that effect)

OR

pressure is lowered by a shift in the equilibrium (from left) to right/favours forward reaction.

2

(d) ΣB(reactants) – ΣB(products) = ΔH (M1)

OR

Sum of bonds broken – Sum of bonds formed = ΔH (M1)

B(H–H) + ½B(O=O) – 2B(O–H) = – 242 (M1)

B(H–H) = – 242 – ½(+496) + 2(+463) (this scores M1 and M2)

B(H–H) = (+)436 (kJ mol–1) (M3)

Award 1 mark for – 436

Candidates may use a cycle and gain full marks. M1 could stand alone Award full marks for correct answer. Ignore units. Two marks can score with an arithmetic error in the working.

3 [11]

Q31. (a) (i) mol CH4 = 0.75

1

mol H2O = 1.5 1

mol H2 = 1(.0) 1

(ii) 0.15 (mol dm–3) conseq = (mol CH4)/5

of 57

1

(b) (i)

not just numbers do not penalise ( ) If wrong Kc no marks for calc but allow units conseq to their Kc

1

(ii) No marks for calc if concs used wrongly or wrong values inserted

1

0.025(4) 1

mol2 dm–6

allow 1 here for correct units from wrong Kc 1

(c) increase if wrong, no further marks in (c)

1

M1 lower P 1

M2 eqm shifts to side with more moles (Le Chatelier) not “greater volume” for M1 but allow “moves to form a greater volume” for M2

1

(d) (forward reaction is) endothermic or backward reaction is exothermic 1

eqm shifts in exothermic direction or to oppose reduction of or change in temp

This mark must have reference to temp change or exothermic reaction

1 [13]

Q32. (a) (i) 4FeS2 + 11O2 2Fe2O3 + 8SO2

2 5½ (1) 4 Or multiples of this equation

1

(ii) M1 (+) 4

M2 – 1

of 57

Ignore working M1, credit (+) IV M2, credit – I

2

(b) M1 Lower/smaller/decreases/reduced yield OR equilibrium shifts (right) to left

M2 (Forward) reaction is exothermic OR reverse reaction is endothermic

M3 (By Le Chatelier’s principle) equilibrium responds/shifts/moves (R to L) to lower the temperature OR to absorb the heat OR to cool the reaction

If M1 is blank, mark on and credit M1 in the text. If M1 is incorrect, only credit correct M2 Mark M2 independently – it may be above the arrow in the equation For M3, not simply “to oppose the change/temperature”

3

(c) M1 Fe2O3 + 3CO 2Fe + 3CO2

Or multiples Ignore state symbols

M2 Reducing agent OR Reduce(s) (Fe2O3/iron(III) oxide) OR Electron donor OR to remove the oxygen (from iron(III) oxide to form CO2) OR reductant

For M2, credit “reduction” 2

[8]

Q33. (a) Kc / Ka / equilibrium constant / constant is temperature dependent

Do not allow ‘affects or shifts equilibrium’. 1

(b) Thermostat / water bath 1

[2]

Q34. (a) Forward and backward reactions proceeding at equal rate

1

Amount (Conc or moles or proportion) of reactants and products remain constant

Not “reactants and products have equal conc” 1

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(b) M1 Allow ( ) but must have all brackets If Kc wrong can only score M3 (process mark) for dividing both R and P by volume)

1

(c) M2 [Q]2 = Rearrangement of correct Kc expression If wrong Kc used can only score M3 for correct use of vol If wrong rearrangement can only score max 2 for M3 and M5 for correct √

1

M3 [Q]2 = Process mark for dividing both R and P by volume even in incorrect expression If vol missed can only score max 2 for M2 and M5 for correct √ If vol used but then wrong maths can score M2 M3 and M5 for correct √ If moles used wrongly, eg (2 × 5.24) or (5.24 × 10/103) can only score M2 and M5

1

M4 [Q]2 = 0.0106 Correct calculation of Q2

1

M5 [Q] = 0.10(3) Correct taking of √

1

(c) cont.

Wrong rearrangement and no use of volume 0

Wrong rearrangement For Correct use of volume M3 and Correct taking of square root M5

2 max

No use of volume 2 max answer = 0.325 Ignore subsequent multiplying or dividing by 10. 0.0325 or 3.25 still score max 2 For Correct rearrangement M2 and Correct taking of square root M5

2 max

of 57

Use of volume but maths error e.g. using (5.24)2/10 when should be (5.24/10)2

Scores 3 also giving answer 0.325 for M2, M3 and M5

3

Use of volume but Q/10 also used or Q multiplied by 10 at end (i.e.muddling moles with concentration)

Gives answer 1.03 For Correct rearrangement M2 and Correct taking of square root M5

2 max

Wrong use of moles, e.g (5.24 × 2) or (5.24 × 10/103) For Correct rearrangement M2 and Correct taking of square root M5

2 max

Wrong Kc used, e.g. missing powers For Correct use of volume M3

1 max

(d) Increase or more or larger Allow moves to left

1

(e) Increase or more or larger Allow moves to left

1

(f) Decrease or less or smaller NOT allow moves left

1

(g) No effect or unchanged or none 1

(h) 0.0147 or 0.0148 or 1.47 × 10-2 or 1.48 × 10-2

Allow 0.015 or 1.5 × 10-2

If not 0.0147, look at (c) for conseq correct use of their [Q] in new Kc = 1.39 × [Q]2

Not allow just 1/68.0 ignore units

1 [24]

Q35. (a) (i) chlorotrifluoromethane

Spelling must be correct but do not penalise “flouro” Ignore use of 1–

1

of 57

(ii) CF3• May be drawn out with dot on C OR if as shown dot may be anywhere

1

(iii) An unpaired/non-bonded/unbonded/free/a single/one/lone electron

NOT “bonded electron” and NOT “paired electron” NOT “pair of electrons” NOT “electrons” Ignore “(free) radical”

1

(b) M1 Cl• + O3 → ClO• + O2

M2 ClO• + O3 → 2O2 + Cl• Mark independently Equations could gain credit in either position The dot can be anywhere on either radical Penalise the absence of a dot on the first occasion that it is seen and then mark on. Do not make the same penalty in the next equation, but penalise the absence of a dot on the other radical. Apply the list principle for additional equations

2

(c) (i) (If any factor is changed which affects an equilibrium), the (position of) equilibrium will shift/move so as to oppose the change.

OR


Must refer to equilibrium Ignore reference to “system” alone A variety of wording will be seen here and the key part is the last phrase. An alternative to shift/move would be the idea of changing/altering the position of equilibrium

1

(ii) M1 The (forward) reaction/to the right is endothermic or takes in heat

OR The reverse reaction/to the left is exothermic or gives out heat

M2 The equilibrium moves/shifts to oppose the increase in temperature M2 depends on a correct statement for M1 For M2 accept The equilibrium moves/shifts • to take in heat/lower the temperature

of 57

• to promote the endothermic reaction and take in heat/ lower the temperature • to oppose the change and take in heat/lower the temperature (leading to the formation of more ozone)

2

(d) Any one of

• Pentane does not contain chlorine OR C–Cl (bond)

• Pentane is chlorine-free

• Pentane does not release chlorine (atoms/radicals) Ignore reference to F OR C–F OR halogen Ignore “Pentane is not a CFC” Ignore “Pentane is a hydrocarbon” Ignore “Pentane only contains C and H” Ignore “Pentane is C5H12”

1 [9]

class: date: - isaac newton academy 12 in 13 chemistry exam packs...state the type of reaction that...

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