synoptic unit practice papers - rm learning platformiii) explain why ammonia molecules can behave in...

moulsham high school 1

moulsham high school

Synoptic Unit Practice papers

Chemistry Department

ANSWER ALL QUESTIONS


1. (a) The scheme below shows three reactions of benzoyl chloride.

CO Cl

benzoyl chloride

compound R

compound P compound Q

water

ammonia methanol

(i) Complete the displayed formulae of P, Q and R.

P Q R (3)

(ii) What type of attacking reagents are ammonia, water and methanol?

��..��. (1)

(iii) Explain why ammonia molecules can behave in this way but ammonium ions cannot.

��..��.

��..��.

��..��. (1)

(b) Another compound which can be prepared from benzoyl chloride is the ester phenyl benzoate, C6H5CO2C6H5. Name the other organic compound required for this reaction and state the necessary conditions.

Compound ��

Conditions �� (2)


(c) (i) Phenyl benzoate prepared by the reaction in (b) is first seen as off�white �lumps� of

solid. This solid is filtered off and is then purified by recrystallization. This technique involves dissolving the impure phenyl benzoate in the minimum quantity of a hot solvent. Pure phenyl benzoate crystallizes out when the solution is cooled.

Explain why the final product is of higher purity than the original off�white solid.

��..��.

��..��.

��..��.

��..��.

��..��.

��..��. (2)

(ii) How could you check the purity of the recrystallized phenyl benzoate?

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��..��. (2)

(d) Many esters are fragrant liquids and some of them are used as constituents of perfumes. Suggest TWO properties (apart from smell and safety in use) an ester needs if it is to be suitable for this use.

��.

��. (2)

(Total 13 marks)

2. Iron(III) chloride reacts with potassium ethanedioate to form potassium triethanedioatoferrate(III) according to the equation:

FeCl3(aq) + 3K2(C2O4)(aq) ��→ K3[Fe(C2O4)3](aq) + 3KCl(aq)

(a) What is the name given to an ion like [Fe(C2O4)3]3�(aq)?

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


(b) What is the mass of 1 mole of K3[Fe(C2O4)3]?

Show your working and use the Periodic Table as a source of data.

(2)

(Total 3 marks)

3. A Born�Haber cycle for magnesium sulphide is shown below:

Mg (g)

Mg(g)

2+ S (g)

S(g)

2� MgS(s)

2

+

Mg(g) S(g)+

∆H ∆H

∆H

∆H

∆H ∆H

4

1

5

3

6

2

(a) Which symbol in the list represents the lattice energy of magnesium sulphide?

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

(b) (i) Use the data to calculate H5.

Include a sign and units, giving your answer to 3 significant figures.

(3)

(i) Write an equation to represent the first electron affinity, Eaff [S(g)], of sulphur.

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


(iii) Eaff [S(g)] has a value of �200 kJ mol�1. Calculate the second electron affinity of

sulphur, using your value of H5. Include a sign and units in your answer.

(2)

(iv) Explain why the two electron affinities have opposite signs.

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

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

(c) (i) ∆H4 is the sum of two enthalpy changes. Name both of them.

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

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

(ii) Which one would have the larger value?

Justify your answer.

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

(d) In an attempt to show the presence of magnesium in the magnesium sulphide, a flame test was carried out. The solid magnesium sulphide was added to a small volume of concentrated acid, a small portion removed on a wire and then placed in a flame.

(i) Which acid should be used? ................................................................... (1)

(ii) What should the wire be made of? ......................................................... (1)

(iii) Would this prove to be a successful way of testing for the presence of magnesium? Justify your answer.

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

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


(iv) Draw a single, vertical line on the diagram below to represent the energy change

when one electron is lost from the outer shell of the magnesium ion, Mg , in its ground state.

n = ∞n = 5

n = 4

n = 3

n = 2

n =1

3d4s3p

3s

2p

2s

Energy

(2)

(Total 17 marks)

4. Benzene is the starting material for making a number of important organic compounds.

(a) It can be used to make cyclohexane which is needed for the manufacture of nylon.

Draw the displayed formula of cyclohexane.

(1)


(ii) Name the reagent and catalyst used to make cyclohexane from benzene.

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

Catalyst..................................................................................................... (2)

(iii) Severe conditions of 200 °C and 30 atmospheres pressure are used.

Explain why high pressure is needed when operating at the high temperature required for this reaction.

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

(b) Benzene can also be used to make dodecylbenzenesulphonic acid.

12 12

3

25 25CH H CH H

SO H

Step 1 Step 2

Fuming H SO

(i) Give the reagent and catalyst for Step 1.

Reagent

Catalyst (2)

(ii) Both Step 1 and Step 2 involve attack by electrophiles on the benzene ring

Give the formula of the electrophile in Step 2 and explain what is meant by the term electrophile.

Formula

Explanation

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

(iii) State a use of substances like dodecylbenzenesulphonic acid.

(c) Another use for benzene is to make diazo compounds using a sequence of reactions.

2 2NO NH N ClC+

concentratedsulphuric acid

+2

�

phenylamine benzenediazoniumchloride

D

(i) Name substances C and D.


C.........................................................

D......................................................... (2)

(ii) State the type of reaction that occurs when D is converted into phenylamine.

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

(iii) Name a useful class of compounds that can be made from one of the products in this reaction sequence.

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

(d) Benzenediazonium chloride decomposes in aqueous solution to form phenol C6H5OH, and nitrogen. The rate of this reaction can be measured readily.

(i) Suggest a method for measuring the rate of decomposition of benzenediazonium chloride solution.

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(ii) The rate of the reaction was measured at different temperatures. In the table below the data have been converted into values of 1/temperature and In rate.

1 temperature//K

ln rate

3.0 × 10

3.1 × 10

3.2 × 10

3.3 × 10

3.4 × 10

�1.4

�2.6

�3.9

�5.1

�6.3

�3

�1

�3

�3

�3

�3


Plot a graph of ln rate, on the vertical axis, against 1/temperature, on the

horizontal axis.

(3)

(iii) Calculate the activation energy, EA, for the reaction, using your graph and the relationship:

ln rate = constant � )/1( TR

EA

where R = 8.3 J K�1 mol�1

Remember to include a sign and units in your answer which should be given to two significant figures.

(3) (Total 21 marks)

5. (a) (i) The element xenon consists of separate, single atoms. Suggest one piece of evidence supporting the idea that there are forces of attraction operating between xenon atoms at very low temperatures.

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


(ii) How do these forces arise?

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

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

(iii) Why are these forces stronger in xenon than in krypton?

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

(b) The first compound of a noble gas to be prepared was xenon tetrafluoride, XeF4. It was made by direct reaction between xenon and fluorine.

Xe(g) + 2F2(g) ��→ XeF4(s)

(i) Which of the three substances would you expect to have the lowest standard entropy, St? Justify your answer.

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

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

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


(ii) Complete the following table by indicating whether each of the specified changes

for the reaction between xenon and fluorine is positive or negative and justify your answer in each case.

Change Sign(+ or �)

Justification

Total entropy change(∆ )Sl

Entropy change of surroundings( )∆Sh

Enthalpy change of reaction( )∆H

(3)

(c) Sodium fluoride is soluble in water. The dissolving process can be represented by the equation

Na+F�(s) + aq ��→ Na+(aq) + F�(aq)

The enthalpy change accompanying this process is called the enthalpy change of solution.

Its value can be calculated from a Hess cycle using the following data:

Standard enthalpy change of formation, ∆Hf, of NaF(s) �573.6 kJ mol�1

Standard enthalpy change of formation of aqueous sodium ions, Na+(aq) �240.1 kJ mol�1

Standard enthalpy change of formation of aqueous fluoride ions, F�(aq) �332.6 kJ mol�1


(i) Draw and label this Hess cycle.

(2)

(ii) Use your Hess cycle to calculate the standard enthalpy change of solution of sodium fluoride.

Include a sign and units in your answer. (2)

(d) The following letter appeared in a national newspaper:

"Fluoride occurs naturally in water as calcium fluoride, which is good for teeth. Sodium fluoride, which is added to water, is rat poison. Need more be said?"

The solubilities in water of the two compounds are shown below:

CaF

NaF

2 2.3 × 10

9.9 × 10

�5

�5

Solubilitymol/100g water

Using the solubility data and your knowledge of the bonding in the two compounds, comment on the letter.(Calculations are not required.)

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

Letter by J. Webb published in the Daily Mail, Monday, October 28. 1996. (Total 13 marks)


6. This question is concerned with compounds involved in the following sequence of reactions.

The sequence begins with cadaverine, an amine produced during the decomposition of proteins.

CH

CH

CH

CH

CH

CH

CH

CH NH Cl

CH NH + NaCl + H O

CH

CH

CH

CH

CH

CH

NH

NH

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

Cadaverine

compound B

Piperidine

compound A

2HCl(aq)

heat

+2

� + compound C

(a) (i) If you were provided with a sample of cadaverine, what characteristic physical property would you expect to notice that would immediately suggest that it was an amine?

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

(ii) Give the systematic name of cadaverine.

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

(iii) Draw the structural formula of compound A.

(1)

(iv) Identify compound C. (1)


(b) How would you expect the infra�red spectrum of cadaverine to compare with that of

piperidine?


(You are NOT expected to know or to predict the wavenumbers of any specific troughs in either spectrum.)

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

(c) (i) Cadaverine is classed as a primary amine but piperidine is a secondary amine.

Explain the difference in structure of these two types of amines.

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

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

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

(ii) Draw the structural formula of a tertiary amine of your own choice.

(1)

(d) What would you expect to see if aqueous copper(II) sulphate solution was added to a solution of cadaverine?

Explain your prediction.

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

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

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


(i) Suggest the reagent you would use to convert piperidine to compound D below:

CHCH

CHCH

CH N C CHCH NH

CHCH

CHCH

22

22

22

22

22

3

O

Piperidine Compound D

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

(ii) Of what class of compounds is D a member?

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

(Total 12 marks)

7. The following are some common ions of chromium together with their characteristic colours:

[Cr(H2O)6]3+ [Cr(H2O)6]2+ CrO −24

green blue yellow

An orange solution of potassium dichromate (VI), K2Cr2O7, on treatment with excess sulphuric acid and zinc gives a green solution A and later a blue solution B.

Treatment of acidified potassium dichromate(VI) solution with hydrogen peroxide gives a similar green solution A but not the blue solution B.

When potassium dichromate(VI) solution is treated with excess sodium hydroxide it gives a yellow solution C.

(a) What ion is responsible for the colour of the solution C?

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

(b) (i) What type of reaction is the conversion of A to B?

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


(ii) Quoting electrode potentials from Table 6.1 of the Book of data explain why the

conversion of A to B takes place using zinc but not using hydrogen peroxide.

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................................................................................................................. (3)

(c) The blue solution B on exposure to the air rapidly turns green.

(i) Explain what is happening.

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

(ii) Other than by excluding air, how might the blue solution B be stabilized?

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

(d) (i) Write an ionic equation for the conversion of dichromate(VI) ions to C. (2)

(ii) Is this a redox reaction? Justify your answer.

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

(e) (i) A green solution of chromium(III) ions, on treatment with aqueous ammonia, gives a green precipitate in which the original hydrated chromium(III) ions have each lost three protons.

What is the formula of the precipitate?

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

(ii) When more ammonia solution is added to the reaction mixture in (e)(i), the green precipitate slowly dissolves to give a deep violet solution in which ammonia molecules are ligands.

Suggest a formula for the complex ions formed.

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

(Total 15 marks)

8. One step in the extraction of gold from its ore uses oxygen in the presence of aqueous


sodium cyanide:

A 4Au(s) + 8CN�(aq) + 2H2O(l) + O2(g) → Au(CN)−2 (aq) + 4OH�(aq)

The resulting aqueous solution is then treated with zinc which re-precipitates the gold.

(a) The redox process in equation A may be divided up into two electrode systems. One of these is given as B below; write in the other one as C:

B Au(CN) −2 (aq), 2CN�(aq) | Au(s) Et = +0.12V

C [��.], ��.| Pt Et = +0.40V (2)

(b) Draw a diagram of a half�cell based on B. No salt bridge or hydrogen electrode need be shown but the diagram should be labelled and concentrations given where appropriate.

(4)

(c) (i) Combine B and C into a cell diagram with the electrode B as the left-hand electrode.

(2)

(ii) Calculate Et for the cell you have represented in (c)(i). Give a sign and units in your answer.

(2)

(iii) What does your answer suggest about the position of equilibrium of reaction A at 298 K? Justify your answer.

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

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

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

(d) What shape would you expect for the complex ion Au(CN) −2 ?

(1)


(e) One of the problems in extracting gold in this way is that the metal is trapped in a matrix

of minerals such as arsenopyrite, FeAsS, which cannot easily be broken down. In some cases only 10% of the available gold is actually extracted.

This problem has recently been solved by using bacteria to catalyse reactions such as:

2FeAsS(s) + 7O2(g) + 4H+(aq) + 2H2O(l) → 2Fe3+(aq) + 2H3AsO4(aq) + 2HSO −4 (aq)

(i) Assuming that arsenopyrite contains sulphide ions, S2�, what oxidation numbers does this suggest for iron and arsenic?

Fe............................ As.................................... (2)

(ii) Why would it be environmentally unacceptable simply to heat the arsenopyrite strongly in air in order to break it down?

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

(Total 17 marks)

9. An elastic tape is labelled as consisting of 59% polyester and 41% of a polymer similar to synthetic rubber, neoprene. Neoprene is a polymer of 2�chlorobuta�1,3�diene which polymerizes according to the partially�completed equation

C C C C C C C Cnn

(a) On the following copy of the right�hand side of this equation fill in the appropriate side-groups in the formula for neoprene:

C C C Cn

(2)

(b) (i) What type of polymerization process is illustrated in the equation shown above?

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

(ii) What name is given to the type of polymer to which both neoprene and natural rubber belong?

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

(c) Polyester is made by a reaction between benzene� 1,4�dicarboxylic acid and ethane� 1,2�


diol:

CO H

CO H

2

2 2

2

HO CH CH OH

Draw a structural formula to show the molecule which results when one molecule of each of these monomers are joined by an ester linkage.

(2)

(d) Suggest why the manufacturer considers it desirable to use a mixture of polyester and neoprene for making elastic tape.

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

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

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

(e) Suggest a reagent which would react with neoprene but which would not react with polyester. Give an observation and a brief explanation of the reaction.

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

Observation and explanation..........................................................................

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

.................................................................................................................................... (3)

(f) Suggest TWO properties, not already referred to in this question, which have to be considered when choosing a polymer for making a garment.

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

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

(Total 13 marks)

10. In this question you are asked to collect electrode potential data and assemble them in an appropriate order. Before beginning to write your answer, read the instructions for(a) all the way through.

(a) From the Book of data, Table 6.1, list in order the electrode systems and potentials corresponding to the reduction of each of the halogen elements chlorine. bromine and iodine to their respective simple ions, Hal�.

Put into your list, in appropriate places, items numbered 19, 40, 54 and 55. Another source of data gives the following equation and corresponding electrode

potential:


2SO −24 (aq) + 10H+(aq) + 8e� → S2O −2

3 (aq) + 5H2O(l) Et = +0.57V

Put this equation into the same format as the rest of the data and include this item in your list.

(4)

(b) What is the maximum oxidation number of sulphur which can be achieved by the action of thiosulphate ions with

(i) iodine in neutral solution (ii) chlorine? (2)

(c) The concentration of a solution of iodine can be estimated by titration with sodium thiosulphate. Suggest why bromine cannot be estimated in the same way.

(1)

(d) Suggest why the species in which the oxidation number of sulphur is +4 is represented by the formula SO −2

3 in one of these electrode systems but H2 SO3 in another.

(3)

(e) It is suggested that sulphur in the thiosulphate ion might disproportionate.

(i) Under what conditions might this take place, according to the electrode potentials? (2)

(ii) Write a balanced ionic equation for this disproportionation. (2)

(iii) If this disproportionation happens, what change would you expect to see taking place?

(1) (Total 15 marks)


11. The quality of written communication will be assessed in this question. To gain full marks

you must explain your ideas clearly using equations and diagrams where appropriate.

(a) Name and describe the type of bonding present in each of the following:

(i) gaseous chlorine

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(ii) liquid mercury

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(iii) solid mercury(ii) chloride.

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(6)


(b) Construct a Born-Haber cycle for mercury(II) chloride.

Use it to calculate a value for the electron affinity of chlorine. The lattice energy of mercury(II) chloride is �2651 kJ mol�1.

(5)

(c) List the values of electron affinities of the halogens bromine and iodine, from table 5.10 in the Book of Data. Use these values and your answer to (b) to state and explain the trend in the values of electron affinities of the halogens.

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(Total 13 marks)




This question is about hydroxylamine, NH2OH.

Hydroxylamine can be thought of as being derived from ammonia, NH3, by the replacement of one hydrogen atom by a hydroxyl, OH, group.

(a) Draw a �dot-and-cross� diagram for hydroxylamine. Use it to predict the HNH and NOH bond angles.

HNH bond angle .......................................................................................................

NOH bond angle ....................................................................................................... (3)

(b) (i) What would you expect the pH of an aqueous solution of hydroxylamine to be? Justify your answer and write an equation for the equilibrium reaction between water and hydroxylamine.

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

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.......................................................................................................................... (3)

(ii) Would you expect hydroxylamine to form complexes with transition metal ions? Justify your answer.

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


(c) The following experiment was carried out to determine the equation for the reaction

between iron(III) ions, Fe3+(aq), and hydroxylamine, NH2OH(aq).

250 cm3 of an aqueous solution, containing 0.370 g of hydroxylamine, was prepared using a volumetric flask. 25.0 cm3 of this solution was reacted with excess acidified iron(III) sulphate solution.

The iron(II) ions produced were converted back to iron(III) ions by titrating with potassium manganate(VII) solution. The equation for this reaction is:

5Fe2+(aq) + MnO −4 (aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

22.4 cm3 of 0.0200 mol dm�3 potassium manganate(VII) was required.

(i) How can you detect the end-point of this titration?

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

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

(ii) Calculate the number of moles of iron(II) ions which reacted with the 22.4 cm3 of potassium manganate(VII) solution. This will also be the number of moles of iron(III) ions which reacted with the hydroxylamine.

(1)

(iii) How many moles of hydroxylamine were present in the 25.0 cm3 of solution used in the titration?

(1)

(iv) Use your answers to (ii) and (iii) to deduce the number of moles of iron(III) ions which react with one mole of hydroxylamine.

(1)

(v) What is the oxidation number of nitrogen in hydroxylamine?

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


(vi) Use oxidation numbers and the number of moles reacting, to show which of the

following nitrogen products, NO, N2O, N2O4, N2, and NH3, is likely to form in the reaction between hydroxylamine and iron(III) ions.

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

(vii) Hence, write a balanced equation for this reaction.

(1)

(d) Write a cell diagram for the redox reaction between manganate(VII) ions and iron(II) ions.

5Fe2+(aq) + MnO −4 (aq) + 8H+(aq) 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

Calculate Eο and comment on the position of equilibrium.

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(Total 17 marks)




This question is about the reaction sequence shown below

(a) Compound A has the composition, by mass, 70.5% carbon, 13.7% hydrogen and 15.8% oxygen. Show that this percentage composition is consistent with the molecular formula C6H14O.

(2)


(b) Deduce the displayed formula for A showing how you used each of the following pieces

of information.

1 Infra-red spectrum.

2 Mass spectrum.

3 On dehydration, only a single isomer B can be formed.

(6)

1 Infra-red spectrum of A.


2 A simplified mass spectrum of A.

(c) By drawing part of the chain formed from two monomer units, show the structural formula of the polymer C.

(1)


(d) Both compounds D and E are chiral and compound E is an isomer of compound A.

(i) Draw diagrams to show the two optical isomers of compound D and suggest how they could be distinguished.

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

(ii) Give the systematic name for compound E.

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(e) Would you expect the conversion of compound D to compound E to be a first or second order reaction? Justify your answer.

��.........................................................................................................................

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��......................................................................................................................... (2)

(f) Name the THREE oxidation products obtainable from compounds A and E.

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��......................................................................................................................... (2)

(Total 16 marks)


14. This question is about two ingredients which may be found in a washing powder.

(a) One ingredient is the detergent sodium 4-dodecylbenzenesulphonate

This detergent can be manufactured from benzene in three steps.

(i) Outline how to make 4-dodecylbenzenesulphonic acid from benzene in TWO steps. For each step, give the reactants and essential conditions.

(3)

(ii) The manufacturer carries out the third step by reacting the 4-dodecylbenzene sulphonic acid with sodium hydroxide to form sodium 4-dodecylbenzene sulphonate. Suggest TWO reasons why the sulphonate, rather than the sulphonic acid, is used in the washing powder.

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

(b) A second ingredient in the washing powder is the enzyme subtilisin, which breaks down proteins into amino acids.

(i) What is the name given to this type of reaction?

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


(ii) By using the dipeptide, leu-gly, write a balanced equation to illustrate this type of

reaction. Use structural formulae throughout.

The formulae for amino acids can be found on page 436 of the Students’ Book.

(3)

(iii) Describe how you could identify the two amino acids, leucine and glycine, in the products of this reaction. Your answer should include a labelled diagram, drawn to scale, of the expected results.

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(4)

(c) Why does the manufacturer of this washing powder recommend using it at 40 °C?

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

(Total 14 marks)


15. The substance R is chiefly responsible for the smell of ripe raspberries.

(a) Analysis of R showed that it contained 73.2% carbon, 7.3% hydrogen and 19.5% oxygen by mass.

The molar mass of R is 164 g mol�1. Calculate the empirical formula and the molecular formula of R.

(2)

(b) The following tests were carried out on samples of R. For each test and its result, state what can be deduced about the structure of R.

(i) R burnt with a very sooty flame.

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(ii) R reacted with sodium to give off hydrogen gas.

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(iii) R produced a slightly acidic solution in water, but did not react with sodium carbonate solution.

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(iv) R gave an orange precipitate with Brady�s reagent (2,4-dinitrophenylhydrazine).

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

(v) R did not react when warmed with Benedict�s solution.

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(vi) A solution of R rotated the plane of plane-polarised light.

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


(vii) The infra-red spectrum of R had an absorption at 830 cm�1.

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

(c) Deduce a displayed formula for R.

(1)

(Total 11 marks)

16. This question is about nickel compounds.

(a) Hydrated nickel(II) salts are green in colour. Give the electron configuration of a nickel(II) ion and hence state why the ion is coloured.

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(b) (i) Which is the only nickel compound, in Table 5.3 in the Book of Data, in which the nickel atom does not have an oxidation number of +2?

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(ii) What is the oxidation number of nickel in this compound?

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(c) Nickel(II) chloride solution contains the ion Ni(H2O)62+(aq). On adding ammonia

solution, the colour changes to blue or purple as different complexes are formed.

(i) Write the equation, including state symbols, for the displacement of one water molecule by an ammonia molecule.

(1)


(ii) Would you expect ∆Ssystem for this reaction to be positive, negative or close to zero? Justify your answer.

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(d) The complexes formed when ammonia solution is added to nickel(II) chloride solution have the formula [Ni(H2O)x(NH3)6�x]Cl2. An experiment was carried out to determine the value of x in one of them.

A sample of 5.000 g of this complex was dissolved in water and reacted with excess silver nitrate. 6.133 g of silver chloride was produced.

(i) Write the ionic equation, including state symbols, for the formation of silver chloride.

(1)

(ii) Calculate the number of moles of silver chloride produced.

Each mole of the complex contains two moles of chloride ions. Calculate the number of moles of the complex present in the 5.000 g sample.

Hence calculate the mass of one mole of the complex.

(3)


(iii) Use your answer in (ii) to calculate the value of x and hence the formula of this

complex ion.

(1)

(iv) Draw TWO possible structures for this complex ion.

(2)

(Total 14 marks)

17. The enthalpy change of solution of silver fluoride can be determined by using the following adaptation of the Born-Haber cycle.

(a) What is the name of the enthalpy change, ∆H1ο?

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(b) (i) Calculate ∆H4

ο, using your Book of Data to look up necessary enthalpy data.

(2)

(ii) Look up the value of ∆H3ο, in Table 5.6 in the Book of Data, and hence calculate

the value of ∆H2ο for the reaction

Ag+(g) + F�(g) → Ag+(aq) + F�(aq)

(3)

(iii) Apply Hess�s Law to calculate ∆Hοsolution of silver fluoride.

(1)

(c) (i) Calculate ∆Sοsurroundings, ∆Sοsystem and ∆Sοtotal for this reaction at 298 K.

Ag+F�(s) → Ag+(aq) + F�(aq)

Use the Book of Data where necessary.

(3)


(ii) What does the sign of ∆Sοtotal suggest about the solubility of silver fluoride?

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(Total 11 marks)

18. The cyclic amide hydantoin, F, can be prepared from 2-aminoethanoic acid, A, in three steps.

(a) A is an amino acid. How does it differ from other naturally-occurring amino acids?

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(b) Name reagent B and the TWO types of reaction occurring when A is converted into C.

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(c) Reagent D is potassium cyanate. Draw a �dot-and-cross� diagram for the cyanate ion,

NCO�. Predict the NCO bond angle.

(2)

(d) (i) When E is converted into F, what other compound is produced?

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(ii) When F reacts with hot, dilute hydrochloric acid, A is re-formed with other products. What type of reaction is this? Name TWO of the other products.

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(iii) Would you expect hydantoin, F, to be soluble in water? Justify your answer.

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(e) A can form a polymer. Give the formula of part of the polymer chain, showing two monomer units only.

(1)

(Total 13 marks)


19. Sulphide ions, S2�, react with concentrated nitric acid to form nitrogen(II) oxide, NO, and

sulphur.

(a) On the electrode potential chart, display the data for the electrode systems numbered 22, 70 and 78 from Table 6.1 in the Book of Data.

+8 +7 +6 +5 +4 +3 +2 +1 0 �1 �2Oxidation number

E / V

�0.5

0

+0.5

+1.0

(3)


(b) (i) The reaction takes place in two steps. Use the electrode potential chart to calculate

Eο for each of the two steps. Write the overall equation for the reaction.

(4)

(ii) Comment on the position of equilibrium.

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(iii) What would you expect to see as the reaction proceeds?

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(Total 11 marks)


20. Hydrolysis of a dipeptide, W, produces two amino acids, X and Y.

(a) The chromatogram formed by an aqueous solution of the amino acids X and Y, with a butan-1-ol/ethanoic acid/water mixture, is shown below.

Calculate the Rf value for each acid, clearly showing any measurements that you make.

(2)

(b) An aqueous solution of X has no effect on the plane of plane-polarised light. An aqueous solution of Y rotates the plane of plane-polarised light. Identify amino acids X and Y. Refer to the table on page 436 of the Students’ Book.

X ..................................................................................................................................

Y .................................................................................................................................. (2)

(c) Suggest why each of these amino acids moves a different distance up the chromatogram.

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(d) What feature of the molecule of Y causes its aqueous solution to rotate the plane of plane-

polarised light?

Draw appropriate formulae for Y to illustrate your answer.

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(e) Draw the TWO possible structural formulae of the dipeptide, W.

(2)

(Total 9 marks)


21. (a) (i) Draw a fully labelled diagram of the Born-Haber cycle for the determination of the

lattice energy of calcium chloride.

Calculate the lattice energy of calcium chloride using your Born-Haber cycle. Give your answer to four significant figures.

(5)

(ii) Give a reason for the difference between your value and the theoretical value, from the Book of Data, for the lattice energy of calcium chloride.

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(b) Give the ionic radii, ri, for the germanium ion, Ge4+, and the chloride ion, Cl�, using

Table 4.4 in the Book of Data.

Predict the type of bond between germanium and chlorine, and the structure of germanium(IV) chloride, using your values and Fajans� rules.


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(c) (i) Write a balanced equation, with state symbols, showing what happens when calcium chloride is added to water.

(1)

(ii) Suggest a balanced equation, with state symbols, for the reaction which occurs when germanium(IV) chloride is added to water.

(1)

(Total 12 marks)


22. (a) A liquid hydrocarbon, A, has the molecular formula C6H10.

A has a boiling point of 356.5 K.

On complete combustion, 4.1 g of A forms 7.2 dm3 of carbon dioxide, and 4.5 g of water.

[Molar volume of a gas is 24 dm3 under the conditions of the experiment.]

(i) Write the empirical formula of A and use the combustion data to show that the empirical formula is correct.

Empirical formula of A .........................................................................................

(3)

(ii) A reacts with an excess of bromine water to form B, C6H10Br2. Suggest structural formulae of A and B.

(2)

(iii) B reacts with ammonia to produce C, C6H14N2. Give the structural formula for C.

State appropriate conditions, and write the balanced equation, for this reaction.

(4)


(b) Compound C reacts with hexanedioyl dichloride to produce a polymer.

Draw the structure of part of the polymer to show TWO repeating units. State the type of polymerisation involved in making this polymer.

(2)

(Total 11 marks)

23. This question is about hydrogen peroxide, H2O2, and its decomposition.

(a) Draw a �dot and cross� diagram to show the electron structure for hydrogen peroxide, showing outer electrons only.

Draw a displayed formula to show the shape of a molecule of hydrogen peroxide.

State the O O H bond angle.

(3)

(b) Hydrogen peroxide is a liquid at room temperature. Suggest the principal intermolecular force between hydrogen peroxide molecules.

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(c) Hydrogen peroxide decomposes slowly at room temperature.

2H2O2(aq) → O2(g) + 2H2O(l)

(i) Explain, using oxidation numbers, why this is a disproportionation reaction.

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(ii) Suggest, with a reason, the sign of the entropy change of the system for this reaction.

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(d) The reaction in (c) is catalysed by iron(II) ions in aqueous solution, Fe2+(aq).

(i) What type of catalyst are iron(II) ions in this reaction?

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(ii) Add the electrode potentials and half equations relevant to the decomposition of

hydrogen peroxide to the chart below, using the items of data numbered 65 and 102 in Table 6.1 in the Book of Data. Use the chart to suggest how iron(II) ions catalyse this reaction.

E /V

+0.5

+1.0

+1.5

+2.0

+3 +2 +1 0 �1 �2 Oxidationnumber

Fe + e Fe3+ 2+�

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(Total 11 marks)

24. This question is about the element chromium and its compounds.

(a) (i) State the full electronic configuration of a chromium atom in the ground state, using the s,p,d notation.

(1)


(ii) Apart from differing numbers of electrons, how does the ground state electronic

configuration of chromium differ from those of the two adjacent elements in the Periodic Table, vanadium and manganese? Suggest the reason for this difference.

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(b) Compounds containing the chromium(II) ion, Cr2+, are unstable in aqueous solution because they are readily oxidised by oxygen in the air. State the appropriate electrode potentials and half-cells, and use them to explain why this oxidation takes place.

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(c) A useful method of stabilising an unstable oxidation state is to form a complex. You may have prepared chromium(II) ethanoate, Cr2(CH3CO2)4(H2O)2, where the Cr2+ ion is stabilised in this way. [Details can be found on pages 464�465 of your Students’ Book.]

(i) Explain how water acts as a monodentate ligand in this complex.

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(ii) What type of ligand is the ethanoate ion in this complex?

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(iii) Deduce the number of hydrogen peaks in the NMR spectrum of the complex from the structural formula Cr2(CH3CO2)4(H2O)2. Justify your answer.

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(iv) Suggest TWO characteristic absorptions in the infra-red spectrum of the complex.

You should state the bond associated with each absorption and give the corresponding absorption value in wavenumbers.

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(d) (i) When first introduced, breathalysers used acidified sodium dichromate(VI) crystals to detect ethanol on the breath. Using oxidation numbers, or otherwise, balance the equation for the reaction.

C2H6O + Na2Cr2O7 + H2SO4 → C2H4O + Cr2(SO4)3 + H2O + Na2SO4

(2)

(ii) State the colour change you would expect to see if exhaled air containing an excessive amount of ethanol reacted with the breathalyser chemicals.

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(iii) What hazard is associated with the use of sodium dichromate(VI)?

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(Total 17 marks)

synoptic unit practice papers - rm learning platformiii) explain why ammonia molecules can behave in...

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