1. one cause of low-level smog is the reaction of ozone, o

1. One cause of low-level smog is the reaction of ozone, O3, with ethene, C2H4. The smog contains methanal, HCHO(g).

The equation for methanal production is shown below.

O3(g) + C2H4(g) → 2HCHO(g) + ½ O2(g)

The rate of the reaction was investigated, using a series of different concentrations of either C2H4(g) or O3(g), by measuring the initial rate of formation of HCHO(g).

The results are shown below.

experiment[O3(g)]/ 10–7mol dm–3

[C2H4(g)]/ 10–8 mol dm–3

initial rate/ 10–12 mol dm–3 s–1

1 0.5 1.0 1.0

2 2.0 1.0 4.0

3 4.0 2.0 16.0

(i) Analyse and interpret the results to deduce the order of reaction of each reactant and the rate equation.

Explain your reasoning.

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........................................................................................................................[5]

(ii) Calculate the value of the rate constant and state the units.

rate constant =.............................. units…….[3]

(iii) Using the equation above, deduce the initial rate of formation of O2(g) in experiment 1.


answer = ................................. mol dm–3 s–1

[1]

(iv) The experiment was repeated at a higher temperature.

How would the new conditions affect the rate of the reaction and the value of the rate constant?

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

........................................................................................................................[1]

[Total 10 marks]

2. Nitrogen monoxide, NO, is involved in formation of ozone at low levels.

Nitrogen monoxide is produced by combustion in car engines. Ozone is then formed following the series of reactions shown below.

NO(g) + ½O2(g) → NO2(g)

NO2(g) → NO(g) + O(g)

O2(g) + O(g) → O3(g)

Write the overall equation for this reaction sequence.

Identify the catalyst and justify your answer.

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.................................................................................................................................[Total 3 marks]

3. This question looks at the chemistry of transition elements.

(a) (i) Explain what is meant by the terms transition element, complex ion and ligand,

(ii) Discuss, with examples, equations and observations, the typical reactions of transition elements.

In your answer you should make clear how any observations provide evidence for the type of reaction discussed.

[11]

(b) Describe, using suitable examples and diagrams, the different shapes and stereoisomerism shown by complex ions.

In your answer you should make clear how your diagrams illustrate the type of stereoisomerism involved.

[9]

[Total 20 marks]

4. Mercury thermometers are not used in some laboratories because of the danger of mercury vapour. This vapour is very easily absorbed through the lungs into the blood.

In the blood, mercury reacts with hydrogen peroxide to form mercury(II) oxide.

Hg + H2O2 → HgO + H2O

The mercury(II) oxide formed accumulates within organs in the body.

Use oxidation numbers to show that the reaction between mercury and hydrogen peroxide is an example of both oxidation and reduction.

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.................................................................................................................................[Total 2 marks]

5. Mercury forms two ions, Hg22+ and Hg2+. The table shows the electronic configuration

of mercury in these ions.

ion electronic configuration

Hg22+ [Xe]4f145d106s1

Hg2+ [Xe]4f145d10

Use the electronic configurations to explain why mercury is not a transition element.

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.................................................................................................................................[Total 1 mark]

6. A sample of iron is heated with a stream of dry hydrogen chloride. A different chloride of iron is formed that contains the Fe2+ ion. This chloride dissolves in water to form a pale green solution that contains the hexaaquairon(II) complex ion.

(i) Complete the electronic configuration of Fe2+.

1s22s22p6 .......................................................................................................[1]

(ii) Draw the shape of the hexaaquairon(II) complex ion. Include the bond angles on your diagram.

[2]

(iii) Aqueous sodium hydroxide is added to a solution containing Fe2+(aq).

State what you would observe.

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

Write an ionic equation, with state symbols, for the reaction.

........................................................................................................................[2]

[Total 5 marks]

7. The percentage purity of a sample of manganese(IV) oxide, MnO2, can be determined by its reaction with acidified iron(II) ions.

• Stage 1 – A sample of known mass of the impure MnO2 is added to a conicalflask.

• Stage 2 – The sample is reacted with a known excess amount of Fe2+ acidifiedwith dilute sulphuric acid.

• Stage 3 – The contents of the flask are heated gently.

• Stage 4 – The cooled contents of the flask are titrated with aqueous potassiummanganate(VII) in acidic conditions to find the amount of unreactedFe2+.

(i) The reduction half-equation for manganese(IV) oxide in the presence of dilute acid is shown below.

MnO2(s) + 4H+(aq) + 2e– → Mn2+(aq) + 2H2O(l)

Construct the balanced equation for the redox reaction between Fe2+(aq), MnO2(s) and H+(aq).

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

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

........................................................................................................................[1]

(ii) In Stage 1 and Stage 2 a student uses a 0.504 g sample of impure MnO2 and 100 cm3 of 0.200 mol dm–3 Fe2+.

In Stage 4 the student determines that the amount of unreacted Fe2+ is 0.0123 mol.

1 mol of MnO2 reacts with 2 mol of Fe2+.

Calculate the percentage purity of the impure sample of MnO2.

percentage purity = ..................................................... %[3]

[Total 4 marks]

8. Ruthenium (Ru) is a metal in the second transition series. It forms complex ions with the following formulae.

A = [Ru(H2O)6]3+

B = [Ru(H2O)5Cl]2+

C = [Ru(H2O)4Cl2]+

(a) (i) What is the oxidation number of ruthenium in B?

oxidation number of ruthenium = .........................................................[1]

(ii) One of the complex ions, A, B or C, shows stereoisomerism.

Draw diagrams to show the structures of the two isomers.

[2]

(iii) Name this type of stereoisomerism.

...............................................................................................................[1]

(b) The complex ion [Ru(H2O)6]3+ can be converted into [Ru(H2O)5Cl]2+.

(i) Suggest a suitable reagent for this conversion.

...............................................................................................................[1]

(ii) What type of reaction is this?

...............................................................................................................[1]

[Total 6 marks]

9. The standard electrode potential of Cu2+(aq) + 2e– Cu(s) is +0.34 V.

A student measured the standard electrode potential of Cu2+(aq) + 2e– Cu(s). She was surprised to see that the emf of the cell was less than the expected value of +0.34 V.

She decided to measure the concentration of the Cu2+(aq) ions in the solution by titration.

25.00 cm3 of the solution containing Cu2+ ions were pipetted into a volumetric flask and she made the volume up to 250.0 cm3 with distilled water.

An excess of aqueous potassium iodide, KI, was added to 25.00 cm3 of the diluted solution.The iodine formed was titrated against 0.100 mol dm–3 sodium thiosulphate, Na2S2O3.

The volume of Na2S2O3(aq) used was 23.20 cm3.

The equations for the formation and titration of iodine are given below.

2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq)

I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O6

2–(aq)

(i) State how the student would identify the end point of the titration.

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

........................................................................................................................[1]

(ii) Show that the concentration of the Cu2+(aq) ions was 0.93 mol dm–3.

[4]

(iii) Explain, in terms of chemical equilibrium, why the emf of this cell was less than the standard electrode potential.

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[Total 7 marks]

10. Iron forms several complex ions in which the oxidation state of iron is +3.

(i) Complete the electronic configuration for an iron(Ill) ion, Fe3+.

1s22s22p6 .......................................................................................................[1]

(ii) Explain, using electronic configuration, why iron is a transition element.

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

........................................................................................................................[1]

[Total 2 marks]


One of these complex ions is [Fe(CN)6]3–. This is called the hexacyanoferrate(III) ion. In the hexacyanoferrate(III) ion the cyanide ions, CN–, act as ligands.

(i) Suggest why a cyanide ion can act as a ligand.

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

........................................................................................................................[1]

(ii) Draw the expected shape for the complex ion [Fe(CN)6]3–. Include bond angles and the name of the shape.

[2]

[Total 3 marks]


Excess aqueous sodium hydroxide is added to an aqueous solution containing Fe3+

(aq).

(i) Describe what you would see happen.

........................................................................................................................[1]

(ii) Write an ionic equation, including state symbols, for the reaction that takes place.

........................................................................................................................[2]

[Total 3 marks]

13. An unusual compound of iron has been detected on the surface of the planet Mars. This compound contains the ferrate(VI) ion.

When chlorine is bubbled through a suspension of iron(III) oxide in concentrated aqueous sodium hydroxide, a solution of aqueous sodium ferrate(VI) forms.

The two relevant redox systems are shown below.

Cl2(aq) + 2e– → 2C/–(aq)

Fe2O3(s) + 10OH–(aq) → 2FeO42–(aq) + 5H2O(I) + 6e–

Construct the redox equation for the reaction between chlorine, iron(III) oxide and hydroxide ions.

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.................................................................................................................................[Total 2 marks]


A student uses 1.00 g of iron(III) oxide and makes, on crystallisation, 0.450 g of sodium ferrate(VI), Na2FeO4.

Calculate the percentage yield, by mass, of sodium ferrate(VI).

Show your working.

Express your answer to an appropriate number of significant figures.

percentage yield = ............................ %[Total 4 marks]


Ferrate(VI) ions will decompose in acidic solution as shown in the equation below.

4FeO42–(aq) + 2OH+(aq) → 4Fe3+(aq) + 3O2(g) + 10H2O(l)

Explain, in terms of oxidation numbers, why this decomposition involves both reduction and oxidation.

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.................................................................................................................................[Total 2 marks]


Aqueous sodium ferrate(VI) is a very powerful oxidising agent.

(i) Predict what you would see when aqueous sodium ferrate(VI) is added to aqueous potassium iodide.

Explain your answer.

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

........................................................................................................................[1]

(ii) Aqueous sodium ferrate(VI) will oxidise ammonia into substance X.

Suggest an identity for X.

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[Total 2 marks]

17. Under certain conditions, VO2+ can be converted into VO2+ by reaction with KMnO4.

The equation for the reaction is shown below.

5VO2+ + H2O + MnO4– → 5VO2

+ + Mn2+ + 2H+

What volume, in cm3, of 0.0250 mol dm–3 KMnO4 would be required to convert 20.0 cm3 of 0.100 mol dm–3 VO2+ into VO2

+?

volume of KMnO4 required = ...................... cm3

[Total 3 marks]

18. The ethanedioate ion, C2O42–, can act as a bidentate ligand when it forms complex

ions with a transition metal ion. The structure of the ethanedioate ion is shown below.

(a) What do you understand by the term bidentate ligand?

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

........................................................................................................................[2]

(b) The ethanedioate ion readily forms an octahedral complex ion with Cr3+.

Show the structure and charge of this complex ion.

[3]

[Total 5 marks]

19. The Cr3+ ion forms a complex ion of formula [Cr(C2O4)2(H2O)2]–.

Use this complex to explain what is meant by the term stereoisomerism. Your answer should contain suitable diagrams.

[7]

Quality of Written Communication [1]

[Total 8 marks]

20. The compound FeSO4.7H2O can be used to kill moss in grass. Iron(II) ions in a solution of FeSO4.7H2O are slowly oxidised to form iron(III) ions.

Describe a test to show the presence of iron(III) ions in a solution of FeSO4.7H2O.

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.................................................................................................................................[Total 1 mark]

21. The compound FeSO47H2O can be used to kill moss in grass.

The percentage purity of an impure sample of FeSO4.7H2O can be determined by titration against potassium dichromate(VI), K2Cr2O7, under acid conditions, using a suitable indicator.

During the titration, Fe2+(aq) ions are oxidised to Fe3+(aq) ions.

• Stage 1 – A sample of known mass of the impure FeSO4.7H2O is added to a conical flask.

• Stage 2 – The sample is dissolved in an excess of dilute sulphuric acid.

• Stage 3 – The contents of the flask are titrated against K2Cr2O7(aq).

(i) The reduction half equation for acidified dichromate(VI) ions, Cr2O72–, is as

follows.

Cr2O72–(aq) + 14H+(aq) + 6e– 2Cr3+(aq) + 7H2O(l)

Construct the balanced equation for the redox reaction between Fe2+(aq),Cr2O7

2–(aq) and H+(aq).

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..........................................................................................................................[2]

(ii) In Stage 1, a student uses a 0.655 g sample of impure FeSO4.7H2O.

In Stage 3, the student uses 19.6 cm3 of 0.0180 mol dm–3 Cr2O72– to reach the

end-point.

One mole of Cr2O72– reacts with 6 moles of Fe2+.

Calculate the percentage purity of the impure sample of FeSO4.7H2O.

percentage purity .........................[4]

[Total 6 marks]

22. Dilute aqueous copper(II) sulphate contains [Cu(H2O)6]2+ ions.

(a) Concentrated hydrochloric acid is added drop by drop to a small volume of dilute aqueous copper(II) sulphate. The equation for the reaction taking place is as follows.

[Cu(H2O)6]2+(aq) + 4Cl–(aq) [CuCl4]2–(aq) + 6H2O(l)

(i) Describe the observations that would be made during the addition of the concentrated hydrochloric acid.

...............................................................................................................[1]

(ii) Describe the bonding within the complex ion, [CuCl4]2–.

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...............................................................................................................[2]

(b) Concentrated aqueous ammonia is added drop by drop to aqueous copper(II) sulphate until present in excess. Two reactions take place, one after the other, to produce the complex ion [Cu(NH3)4(H2O)2]2+(aq).

Describe the observations that would be made during the addition of concentrated aqueous ammonia.

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[Total 5 marks]

23. Ammonia is a simple molecule. The H—N—H bond angle in an isolated ammonia molecule is 107°.The diagram shows part of the [Cu(NH3)4(H2O)2]2+ ion and the H—N—H bond angle in the ammonia ligand.

Explain why the H—N—H bond angle in the ammonia ligand is 109.5° rather than 107°.

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.................................................................................................................................[Total 3 marks]

24. Cobalt readily forms complex ions in which the cobalt has an oxidation state of +2.

One complex ion of cobalt is the hexaaquocobalt(II) ion [Co(H2O)6]2+.

(i) What is the co-ordination number of Co2+ in this complex ion?

........................................................................................................................[1]

(ii) Water is acting as a ligand. Explain the meaning of the term ligand.

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[Total 3 marks]

25. Cobalt readily forms complex ions in which the cobalt has an oxidation state of +2.

[Co(H2O)6]2+ readily undergoes the following reaction.

[Co(H2O)6]2+(aq) + 4Cl–(aq) [CoCl4]2–(aq) + 6H2O(l)

(i) What is the shape of each complex in this reaction?

[Co(H2O)6]2+ shape ......................................................................................

[CoCl4]2– shape ......................................................................................[1]

(ii) What colour change would occur on going from left to right in this reaction?

from ..................................................... to .....................................................[1]

(iii) What type of reaction is taking place when [Co(H2O)6]2+ reacts with Cl–?

........................................................................................................................[1]

[Total 3 marks]

26. (a) Co2+ forms the complex [Co(NH3)4Cl2]. This complex exists as two stereoisomers.

(i) Draw diagrams to show the two isomeric forms of this complex.

[2]

(ii) What type of stereoisomerism is shown by this complex?

...............................................................................................................[1]

(b) Cobalt also forms a complex with the formula [Co(H2NCH2CH2NH2)2Cl2]. This complex shows the same kind of isomerism as [Co(NH3)4Cl2] but it also shows a different type of stereoisomerism.

Draw diagrams to show the two isomers of this different type of stereoisomerism.

[2]

[Total 5 marks]

27. Chromium metal and its compounds have a number of important uses.

Cr2O72– ions oxidise I– ions to I2 under acid conditions according to the following

equation.

Cr2O72–(aq) + 6I–(aq) + 14H+(aq) 2Cr3+(aq) + 3I2(aq) + 7H2O(l)

(i) If you carried out this reaction, how could you see that iodine is formed?

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

........................................................................................................................[1]

(ii) How could you use the formation of I2 in this reaction to determine the concentration of a solution of Cr2O7

2– ions?

In your answer

• state the method you would use

• state the reagents used

• show how you would use your results.

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[Total 5 marks]

28. Copper and zinc are both d-block elements but only copper is a transition element. Copper forms compounds containing Cu2+ or Cu+ ions but zinc only forms compounds containing Zn2+ ions.

(a) Use the electronic configurations of Cu2+ and Zn2+ to explain why copper is a transition element and zinc is not.

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

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........................................................................................................................[2]

(b) Suggest two differences between compounds containing Zn2+ and Cu2+ ions.

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[Total 4 marks]

29. Brass is an alloy of copper and zinc.

The percentage of copper and zinc in a sample of brass can be determined by reaction with hydrochloric acid. Only zinc reacts, as shown in the equation below.

Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g)

• A sample of brass powder of known mass is added to an excess of 1.00 mol dm–

3 hydrochloric acid.• The mixture is heated gently and the hydrogen collected is measured once the

reaction has finished.

A student analyses a 1.23 g sample of brass using the method described.The student collects 76.0 cm3 of hydrogen at room temperature and pressure.1 mol of gas molecules occupies 24.0 dm3 at room temperature and pressure.

Calculate the percentage by mass of copper in the sample of brass.Give your answer to an appropriate number of significant figures.

answer .............................................. %[Total 3 marks]

30. Artists between the 13th and the 19th Centuries used a green pigment called verdigris. The artists made the pigment by hanging copper foil over boiling vinegar.

During the preparation of verdigris, copper atoms are oxidised to copper(II) ions.

(i) Write the oxidation half equation for the conversion of copper atoms into copper(II) ions.

........................................................................................................................[1]

(ii) The reduction half equation that takes place is as follows.

O2(g) + 4H+(aq) + 4e– → 2H2O(l)

Construct the equation for the redox reaction between copper, oxygen and hydrogen ions.

[1]

[Total 2 marks]

31. Artists between the 13th and the 19th Centuries used a green pigment called verdigris. The artists made the pigment by hanging copper foil over boiling vinegar.

A sample of verdigris has the formula [(CH3COO)2Cu]2.Cu(OH)2.xH2O.Analysis of the sample shows that it contains 16.3% water by mass.Calculate the value of x in the formula.

answer ...................................................[Total 3 marks]

32. In this question, one mark is available for the quality of spelling, punctuation and grammar.

Iron and its compounds take part in several different types of reaction including ligand substitution, precipitation and redox.

For each type of reaction

• give an example, taken from the chemistry of iron or its compounds• state what you would see• write a balanced equation for your example.

[9]


[Total 10 marks]

33. The edta4– ion forms complex ions with Ni2+(aq).

(a) Complete the electronic configuration of the Ni2+ ion.

Is22s22p6 ........................................................................................................[1]

(b) The edta4– ion has the following structure.

(i) Put a ring around two different types of atom in the edta4– ion that are capable of forming a dative covalent bond with the Ni2+ ion.

[2]

(ii) What feature of these atoms allows them to form a bond with Ni2+?

...............................................................................................................[1]

[Total 4 marks]

34. Platinum forms complexes with a co-ordination number of 4.

(a) (i) Explain the term co-ordination number.

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

...............................................................................................................[1]

(ii) State the shape of these platinum complexes.

...............................................................................................................[1]

(b) The tetrachloroplatinate(II) ion readily undergoes the following reaction.

[PtCl4]x + 2NH3 [Pt(NH3)2Cl2]y + 2Cl–

(i) What type of reaction is this?

...............................................................................................................[1]

(ii) Suggest values for x and y in the equation.

x = ……………

y = ……………[2]

(c) The complex [Pt(NH3)2Cl2]y exists in two isomeric forms.

(i) Draw diagrams to show the structure of these isomers.

[2]

(ii) What type of isomerism is this?

...............................................................................................................[1]

(iii) One of the isomers of [Pt(NH3)2Cl2]y is an important drug used in the treatment of cancer.

How does this drug help in the treatment of cancer?

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...............................................................................................................[2]

[Total 10 marks]

35. Vanadium can exist in a number of different oxidation states. One compound of vanadium is ammonium vanadate(V) and this contains the ion VO3

–. This can be reduced to V2+ in several steps, using zinc metal and aqueous sulphuric acid.

(a) 25.0 cm3 of 0.100 mol dm–3 ammonium vanadate(V) is completely reduced to V2+

(aq) using zinc and aqueous sulphuric acid. The resulting solution is titrated with 0.0500 mol dm–3 MnO4

–(aq) and 30.0 cm3 is required to oxidise the V2+(aq) back to VO3

–(aq).

The half equation for acidified MnO4– acting as an oxidising agent is shown

below.

MnO4– + 8H+ + 5e– Mn2+ + 4H2O

Show that the vanadium has changed oxidation state from +2 to +5 in this titration.

[4]

(b) Suggest an equation for the oxidation of V2+(aq) to VO3–(aq) by MnO4

–(aq) under acid conditions.

........................................................................................................................[2]

[Total 6 marks]

36. A moss killer contains iron(II) sulphate.

Some of the iron(II) sulphate gets oxidised to form iron(III) sulphate. During the oxidation iron(II) ions, Fe2+, react with oxygen, O2, and hydrogen ions to make water and iron(III) ions, Fe3+.

(a) Complete the electronic configuration for Fe3+ and use it to explain why iron is a transition element.

Fe3+:1s22s22p6 ................................................................................................

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

........................................................................................................................[2]

(b) State two typical properties of compounds of a transition element.

1 .....................................................................................................................

2 .....................................................................................................................[2]

(c) Describe how aqueous sodium hydroxide can be used to distinguish between aqueous iron(II) sulphate and aqueous iron(III) sulphate.

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

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

........................................................................................................................[2]

(d) Construct the equation for the oxidation of acidified iron(II) ions by oxygen.

........................................................................................................................[2]

[Total 8 marks]

37. The percentage by mass of iron in a sample of moss killer can be determined by titration against acidified potassium manganate(VII).

• Stage 1 – A sample of moss killer is dissolved in excess sulphuric acid.

• Stage 2 – Copper turnings are added to the acidified sample of moss killer and the mixture is boiled carefully for five minutes. Copper reduces any iron(III) ions in the sample to give iron(II) ions.

• Stage 3 – The reaction mixture is filtered into a conical flask to remove excess copper.

• Stage 4 – The contents of the flask are titrated against aqueous potassium manganate(VII).

(i) Suggest why it is important to remove all the copper in stage 3 before titrating in stage 4.

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

........................................................................................................................[1]

(ii) The ionic equation for the redox reaction between acidified MnO4– and Fe2+ is

given below.

MnO4–(aq) + 8H+(aq) + 5Fe2+(aq) → Mn2+(aq) + 4H2O(l) + 5Fe3+(aq)

Explain, in terms of electron transfer, why this reaction involves both oxidation and reduction.

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

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

........................................................................................................................[2]

(iii) A student analyses a 0.675 g sample of moss killer using the method described.

In stage 4, the student uses 22.5 cm3 of 0.0200 mol dm–3 MnO4– to reach the

endpoint.

Calculate the percentage by mass of iron in the moss killer.

percentage ...................................[4]

[Total 7 marks]

38. Aqueous copper(II) sulphate contains [Cu(H2O)6]2+ ions. Aqueous ammonia is added drop by drop to a small volume of aqueous copper(II) sulphate. Two reactions take place, one after the other, as shown in the equations.

[Cu(H2O)6]2+(aq) + 2OH–(aq) → Cu(OH)2(s) + 6H2O(l)

Cu(OH)2(s) + 2H2O(l) + 4NH3(aq) → [Cu(NH3)4(H2O)2]2+(aq) + 2OH–(aq)

(a) Describe the observations that would be made as ammonia is added drop by drop until it is in an excess.

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

........................................................................................................................[2]

(b) Draw the shape for the [Cu(H2O)6]2+ ion. Include the bond angles in your diagram.

[2]

[Total 4 marks]

39. Water is a simple molecule. The H—O—H bond angle in an isolated water molecule is 104.5°.

The diagram shows part of the [Cu(H2O)6]2+ ion and the H—O—H bond angle in the water ligand.

Explain why the H—O—H bond angle in the water ligand is 107° rather than 104.5°.

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

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.................................................................................................................................[Total 3 marks]

40. Transition metals readily form complex ions when they are combined with a suitable ligand.

What is meant by the following terms?

(i) complex ion

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

........................................................................................................................[1]

(ii) ligand

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

........................................................................................................................[2]

[Total 3 marks]

41. (a) A common ligand which combines with a number of transition metal ions is ethane-1,2-diamine, H2NCH2CH2NH2. This is a bidentate ligand.

Explain the meaning of the term bidentate.

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

........................................................................................................................[1]

(b) The complex [CoCl2(H2NCH2CH2NH2)2] is a neutral molecule. It shows two types of stereoisomerism. Use this molecule to explain what you understand by the term stereoisomerism. Your answer should include diagrams to show clearly the structures of the different isomers in both types of stereoisomerism.

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........................................................................................................................[7]

[Total 8 marks]

42. Potassium dichromate(VI) can be used in a number of redox reactions. The standard electrode potentials for two half reactions are given below.

Cr2O72– + 14H+ + 6e– 2Cr3+ + 7H2O Eο = +1.33 V

I2 + 2e– 2I– Eο = +0.54 V

Acidified potassium dichromate(VI) is added to aqueous potassium iodide to give aqueous iodine.

(i) Construct an ionic equation to show the reaction taking place when acidified potassium dichromate(VI) is added to aqueous potassium iodide.

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

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

........................................................................................................................[2]

(ii) An excess of aqueous sodium thiosulphate was then added. Describe and explain what you would see.

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

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

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

........................................................................................................................[3]

[Total 5 marks]

43. Compound B is an organic base. A student analysed this base by the procedure below.

He first prepared a solution of B by dissolving 4.32 g of B in water and making the solution up to 250 cm3. The student then carried out a titration in which 25.00 cm3 of this solution of B were neutralised by exactly 23.20 cm3 of 0.200 mol dm–3 HCl.

1 mole of B reacts with 1 mole of HCl.

Use this information to calculate the molar mass of base B and suggest its identity.

[Total 6 marks]

44. In this question, one mark is available for the quality of use and organisation of scientific terms.

Copper and iron are typical transition elements. One of the characteristic properties of a transition element is that it can form complex ions.

• Explain in terms of electronic configuration why copper is a transition element.

• Give an example of a complex ion that contains copper. Draw the three dimensional shape of the ion and describe the bonding within this complex ion.

• Transition elements show typical metallic properties. Describe three other typical properties of transition elements. Illustrate each property using copper or iron or their compounds.

[11]


[Total 12 marks]

45. Brass is a widely used alloy of copper. It is possible to analyse a sample of brass by initially dissolving it in concentrated nitric acid.

(a) (i) What other metal is present in brass?

...............................................................................................................[1]

(ii) Give one common use for brass and state the property of brass which makes it ideal for that purpose.

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

...............................................................................................................[1]

(b) During the analysis of brass, 1.65 g of the alloy was reacted with concentrated nitric acid. The resulting solution was neutralised, transferred to a volumetric flask and made up to 250 cm3 using distilled water.

An excess of aqueous potassium iodide was added to a 25.0 cm3 portion of the solution from the volumetric flask and the liberated iodine was titrated with 0.100 mol dm–3 sodium thiosulphate. 20.0 cm3 of aqueous sodium thiosulphate were required to remove the iodine.

(i) What could be used to neutralise the excess nitric acid?

...............................................................................................................[1]

(ii) What indicator is used in the titration of iodine with sodium thiosulphate?

...............................................................................................................[1]

(iii) When is this indicator added to the titration mixture?

...............................................................................................................[1]

(c) The reactions taking place in this titration may be summarised as follows.

2Cu2+ + 4I– → 2CuI + I2

I2 + 2S2O32– → 2I– + S4O6

2–

(i) Calculate the amount, in moles, of sodium thiosulphate in 20.0 cm3 of solution.

answer ......................... mol[1]

(ii) For every one mole of Cu2+ ions present in solution, deduce the amount, in moles, of S2O3

2– ions needed for the titration.

answer ......................... mol[1]

(iii) What is the amount, in moles, of Cu2+ ions present in 25.00 cm3 of solution?

answer ......................... mol[1]

(iv) Calculate the percentage by mass of copper in the sample of brass.

answer ...................... % Cu[3]

[Total 11 marks]

46. The Co2+ ion can form complexes with two different co-ordination numbers.

(a) What is meant by the co-ordination number of a complex ion?

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

........................................................................................................................[1]

(b) The following equilibrium is readily established.

[Co(H2O)6]2+ + 4Cl– [CoCl4]2– + 6H2O

(i) In the boxes below, draw the shape of each complex ion.

[Co(H2O)6]2+ [CoCl4]2–

[2]

(ii) What colour change would you expect to see when an excess of Cl– is added to [Co(H2O)6]2+?

from ............................................... to ..................................................[2]

(iii) Describe how you would move the position of this equilibrium to the left.

...............................................................................................................[1]

[Total 6 marks]


Stereoisomerism is very common in transition metal complexes. Some complexes have found an important use in the treatment of cancer.

(i) Name a transition metal complex used in the treatment of cancer.

........................................................................................................................[1]

(ii) Describe how this complex helps in the treatment of cancer.

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

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

........................................................................................................................[2]

[Total 3 marks]

48. Describe the types of stereoisomerism found in transition metal complexes.

Use suitable examples to illustrate your answer.[8]


[Total 9 marks]

49. The table below shows the enthalpy changes needed to calculate the lattice enthalpy of calcium oxide, CaO.

process enthalpy change/ kJ mol–1

first ionisation energy of calcium +590

second ionisation energy of calcium +1150

first electron affinity of oxygen –141

second electron affinity of oxygen + 791

enthalpy change of formation of calcium oxide –635

enthalpy change of atomisation of calcium +178

enthalpy change of atomisation of oxygen +248

(a) (i) Explain why the second ionisation energy of calcium is more endothermic than the first ionisation energy of calcium.

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

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

...............................................................................................................[2]

(ii) Suggest why the second electron affinity of oxygen is positive.

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

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

...............................................................................................................[2]

(b) Complete the Born–Haber cycle for calcium oxide below.

Use the data in the table to calculate the lattice enthalpy of calcium oxide.

lattice enthalpy = ............................ kJ mol–1

[5]

(c) The lattice enthalpies of calcium oxide and magnesium oxide are different.

Comment on this difference.

In your answer you should make clear how the sizes of the lattice enthalpies are related to any supporting evidence.

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

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

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

........................................................................................................................[3]

[Total 12 marks]

50. Most metals can be extracted by reduction from compounds obtained from their naturally-occurring ores.

Metals such as calcium and magnesium are normally extracted by electrolysis but it is feasible that calcium oxide could be reduced by carbon as shown in the equation below.

CaO(s) + C(s) → Ca(s) + CO(g)

Use the data in the table below to help you answer parts (i)–(iii) below.

CaO(s) C(s) Ca(s) CO(g)

ΔHfο /kJ mol–1 –635 0 0 –110

Sο/J K–1 mol–1 39.7 5.7 41.4 197.6

(i) Calculate the standard enthalpy change for the CaO reduction in the equation.

ΔHο = ............................................ kJ mol–1

[1]

(ii) Calculate the standard entropy change for the CaO reduction in the equation.

ΔSο = ......................................... J K–1 mol–1

[1]

(iii) Calculate the minimum temperature at which the carbon reduction in the equation is feasible.

minimum temperature = ...............................[5]

[Total 7 marks]

51. Use the standard electrode potentials in the table below to answer the questions that follow.

I Fe2+(aq) + 2e– Fe(s) Eο = –0.44 V

II V3+(aq) + e– V2+(aq) Eο = –0.26 V

III 2H+(aq) + 2e– H2(g) Eο = 0.00 V

IV O2(g) + 4H+(aq) + 4e– 2H2O(l) Eο = +0.40 V

An electrochemical cell was set up based on systems I and II.

(i) Write half-equations to show what has been oxidised and what has been reduced in this cell.

oxidation:

reduction:

[2]

(ii) Determine the cell potential of this cell.

Ecell = ......................................................... V[1]

[Total 3 marks]

52. Use the standard electrode potentials in the table below to answer the questions that follow.

I Fe2+(aq) + 2e– Fe(s) Eο = –0.44 V

II V3+(aq) + e– V2+(aq) Eο = –0.26 V

III 2H+(aq) + 2e– H2(g) Eο = 0.00 V

IV O2(g) + 4H+(aq) + 4e– 2H2O(l) Eο = +0.40 V

An electrochemical fuel cell was set up based on systems III and IV.

(i) Construct an equation for the spontaneous cell reaction. Show your working.

[2]

(ii) Fuels cells based on systems such as III and IV are increasingly being used to generate energy.

Discuss two advantages and two disadvantages of using fuels cells for energy rather than using fossil fuels.

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

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

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

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

........................................................................................................................[4]

[Total 6 marks]

53. In this question, one mark is available for the quality of spelling, punctuation and grammar.

The lattice enthalpy of magnesium chloride, MgCl2, can be determined using a Born-Haber cycle and the following enthalpy changes.

name of process enthalpy change / kJ mol–1

enthalpy change of formation of MgCl2(s) –641

enthalpy change of atomisation of magnesium +148

first ionisation energy of magnesium +738

second ionisation energy of magnesium +1451

enthalpy change of atomisation of chlorine +123

electron affinity of chlorine –349

• Define, using an equation with MgCl2 as an example, what is meant by the term lattice enthalpy.

• Construct a Born-Haber cycle for MgCl2, including state symbols, and calculate the lattice enthalpy of MgCl2.

• Explain why the lattice enthalpy of NaBr is much less exothermic than that of MgCl2.

[11]


[Total 12 marks]

54. The standard electrode potential of Cu2+(aq) + 2e– Cu(s) is +0.34 V.

(a) Define the term standard electrode potential.

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

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

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

........................................................................................................................[3]

(b) Complete the diagram to show how the standard electrode potential ofCu2+(aq) + 2e– Cu(s) could be measured.

[3]

[Total 6 marks]

55. Chromium is an important metallic element. Its compounds have a number of different oxidation states.

(a) (i) Give one use of chromium metal and state the property of chromium that makes it suitable for this use.

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

...............................................................................................................[1]

(ii) Complete the electronic configuration of a chromium atom.

1s22s22p6 ..............................................................................................[1]

(b) The following equations relate to half-cells involving iron and chromium ions.

Fe3+ + e– Fe2+ Eο = +0.77 V

Cr2O72– + 14H+ + 6e– 2Cr3+ + 7H2O Eο = +1.33 V

A cell was set up by combining these two half-cells.

(i) Derive a balanced equation for the reaction that would occur when the cell is in use.Explain your reasoning in terms of oxidation and reduction.

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

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

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

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

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

...............................................................................................................[3]

(ii) Determine the emf of the cell under standard conditions.

emf = ...................................................... V[1]

[Total 6 marks]

56. In order to obtain full marks in this question, you must show all your working clearly.

In its reactions, sulphuric acid, H2SO4, can behave as an acid, an oxidising agent and as a dehydrating agent.

The displayed formula of pure sulphuric acid is shown below.

Concentrated sulphuric acid will readily oxidise halide ions to the halogen.

The equation below represents the unbalanced equation for the oxidation of iodide ions by sulphuric acid.

H+ + SO42– + I– → I2 + H2S + H2O

(i) Write the oxidation numbers of sulphur and iodine in the boxes above the equation.

[2]

(ii) Balance the equation above.

[1]

[Total 3 marks]

57. The table below shows the enthalpy changes needed to calculate the enthalpy change of formation of calcium oxide.

process enthalpy change/kJ mol–1

lattice enthalpy for calcium oxide –3459

first ionisation energy for calcium +590

second ionisation energy for calcium +1150

first electron affinity for oxygen –141

second electron affinity for oxygen +798

enthalpy change of atomisation for oxygen +249

enthalpy change of atomisation for calcium +178

(a) (i) Explain why the first ionisation energy of calcium is endothermic.

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

...............................................................................................................[1]

(ii) Explain why the first electron affinity for oxygen is exothermic.

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

...............................................................................................................[1]

(b) (i) Draw a Born-Haber cycle for calcium oxide.

Include

• correct formulae and state symbols• energy changes in kJ.

[3]

(ii) Use your Born-Haber cycle in (i) to calculate the enthalpy change of formation for calcium oxide.

enthalpy change of formation = .........................................[2]

(iii) The lattice enthalpy for iron(II) oxide is –3920 kJ mol–1.

Suggest a reason for the difference in lattice enthalpy between calcium oxide and iron(II) oxide.

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

...............................................................................................................[1]

[Total 8 marks]

58. The standard electrode potentials for some redox systems involving vanadium are shown below.

These are labelled A, B, C and D.

Eο/ V

A VO2+ + 2H+ + e– VO2+ + H2O +1.00

B V3+ + e– V2+ –0.26

C V2+ + 2e– V –1.20

D VO2+ + 2H+ + e– V3+ + H2O +0.34

(a) Which of the vanadium species shown in A, B, C and D is the most powerful oxidising agent?

........................................................................................................................[1]

(b) A student wishes to set up a cell with a standard cell potential of 0.60V.

(i) Which two of the redox systems, A, B, C or D, should he choose?

...............................................................................................................[1]

(ii) Complete the labelling of the following diagram which shows the cell with a standard cell potential of 0.60V.

[4]

(iii) The emf of this cell is only 0.60 V under standard conditions. What do you understand by the expression standard conditions?

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

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

...............................................................................................................[1]

[Total 7 marks]

59. Concentrated nitric acid is a powerful oxidising agent. Concentrated nitric acid oxidisessulphur to sulphuric acid. Nitrogen dioxide and another product are also formed.

(i) Suggest a balanced equation for this reaction.

.........................................................................................................................[1]

(ii) Deduce the change in oxidation number of nitrogen in this reaction.

from ............... to ...............[1]

[Total 2 marks]

60. The standard electrode potential of the Cl2/ Cl– half-cell may be measured using the following apparatus.

(a) Suggest suitable labels for A, B, C and D.

A ....................................................................................................................

B ....................................................................................................................

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

D ....................................................................................................................[2]

(b) The half cell reactions involved are shown below.

Cl2 + e– Cl– Eο = +1.36 V

H+ + e– H2 Eο = 0.00V

(i) Use an arrow to show the direction of flow of electrons in the diagram of the apparatus. Explain your answer.

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

...............................................................................................................[2]

(ii) The values of Eο are measured under standard conditions. What are the

standard conditions?

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

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

...............................................................................................................[2]

(c) The half cell reaction for ClO3–/Cl2 is shown below.

ClO3– + 6H+ + 5e– Cl2 + 3H2O Eο = +1.47 V

What does this tell you about the oxidising ability of ClO3– compared with Cl2?

Explain your answer.

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

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

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

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

........................................................................................................................[2]

[Total 8 marks]

61. The table below shows the enthalpy changes needed to construct a Born-Haber cycle for sodium oxide, Na2O.

process enthalpy change / kJ mol–1

first ionisation energy of sodium +495

first electron affinity of oxygen –141

second electron affinity of oxygen +791

enthalpy change of formation for sodium oxide –416

enthalpy change of atomisation for sodium +109

enthalpy change of atomisation for oxygen +247

(a) Use the table of enthalpy changes to complete the Born-Haber cycle by putting in the correct numerical values on the appropriate dotted line.

[4]

(b) Use the Born-Haber cycle to calculate the lattice enthalpy of sodium oxide.

lattice enthalpy = ....................................kJ mol–1

[2]

(c) Which one of the following compounds has the most exothermic lattice enthalpy?

• calcium bromide• calcium chloride• potassium bromide• potassium chloride

Explain your answer in terms of the ions present.

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

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

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

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

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

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

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

........................................................................................................................[4]

[Total 10 marks]

62. Some standard electrode potentials are shown below.

Eο/VAg+ + e– Ag + 0.80Cl2 + e– Cl– + 1.36Cu2+ + 2e– Cu + 0.34Fe3+ + e– Fe2+ + 0.77I2 + e– I– + 0.54


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

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

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

........................................................................................................................[3]

(b) The diagram below shows an incomplete cell consisting of Cu/Cu2+ and Ag/Ag+ half-cells.

(i) Complete and label the diagram to show how the cell potential of this cell could be measured.

[2]

(ii) On the diagram, show the direction of electron flow in the circuit if a current was allowed.

[1]

(iii) Calculate the standard cell potential.

standard cell potential = ……………………V[1]

(iv) Write the overall cell reaction.

...............................................................................................................[1]

(c) Chlorine will oxidise Fe2+ to Fe3+ but iodine will not. Explain why, using the electrode potential data.

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

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

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

........................................................................................................................[2]

[Total 10 marks]

63. NO2 reacts with oxygen and water to form nitric acid, HNO3. In the atmosphere, this contributes to acid rain. Construct a balanced equation for this formation of nitric acid and use oxidation numbers to show that this is a redox reaction.

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

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

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

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

.................................................................................................................................[Total 2 marks]

64. The table below shows the enthalpy changes needed to calculate the lattice enthalpy of calcium chloride, CaCl2.

process enthalpy change / kJ mol–1

first ionisation energy of calcium +590

second ionisation energy of calcium +1150

electron affinity of chlorine –348

enthalpy change of formation for calcium chloride –796

enthalpy change of atomisation for calcium +178

enthalpy change of atomisation for chlorine +122

(a) The Born-Haber cycle below can be used to calculate the lattice enthalpy for calcium chloride.

(i) Use the table of enthalpy changes to complete the Born-Haber cycle by putting in the correct numerical values on the appropriate dotted line.

[3]

(ii) Use the Born-Haber cycle to calculate the lattice enthalpy of calcium chloride.

answer ........................... kJ mol–1

[2]

(iii) Describe how, and explain why, the lattice enthalpy of magnesium fluoride differs from that of calcium chloride.

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

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

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

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

.................................................................................................................[3]

(b) Explain why the first ionisation energy of calcium is less positive than the second ionisation energy.

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

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

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

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

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

........................................................................................................................[2]

[Total 10 marks]

65. The carbonates and nitrates of Group 2 elements decompose when heated.

(a) Barium nitrate decomposes when heated to make barium oxide, nitrogen dioxide and oxygen.

2Ba(NO3)2(s) → 2BaO(s) + 4NO2(g) + O2(g)

(i) Use oxidation states to explain why this decomposition reaction involves both oxidation and reduction.

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

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

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

...............................................................................................................[3]

(ii) Calculate the enthalpy change of reaction, ∆Hr, in kJ mol–1, for the thermal decomposition of barium nitrate using the enthalpy changes of formation, ∆Hf, given in the table.

compound ∆Hf /kJ mol–1

Ba(NO3)2(s)

BaO(s)

NO2(g)

–992

–558

+33

answer ........................... kJ mol–1

[3]

(b) A student investigates the volume of gas formed when barium nitrate is heated.

The diagram shows the apparatus the student uses.

(i) A 1.31 g sample of barium nitrate is completely decomposed.

Use the equation above to calculate the volume, in cm3, of gas formed at room temperature and pressure.

1 mol of gas molecules occupies 24 000 cm3 at room temperature and pressure.

answer ......................... cm3

[3]

(ii) Suggest one problem that the student may encounter when carrying out the investigation.

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

...............................................................................................................[1]

[Total 10 marks]

66. Chlorine gas may be prepared in the laboratory by reacting hydrochloric acid with potassium manganate(VII). The following standard electrode potentials relate to this reaction.

Cl2 + e– Cl– Eο = +1.36 V

MnO4– + 8H+ + 5e– Mn2+ + 4H2O Eο = +1.52 V


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

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

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

........................................................................................................................[3]

(b) Determine the standard cell potential for a cell constructed from these two redox systems.

[1]

[Total 4 marks]

67. Chlorine gas may be prepared in the laboratory by reacting hydrochloric acid with potassium manganate(VII). The following standard electrode potentials relate to this reaction.

Cl2 + e– Cl– Eο = +1.36 V

MnO4– + 8H+ + 5e– Mn2+ + 4H2O Eο = +1.52 V

(a) Use the half-equations above to:

(i) construct an ionic equation for the reaction between hydrochloric acid and potassium manganate(VII);

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

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

.................................................................................................................[2]

(ii) determine the oxidation numbers of chlorine and manganese before and after the reaction has taken place;

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

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

.................................................................................................................[2]

(iii) state what is oxidised and what is reduced in this reaction.

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

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

.................................................................................................................[2]

(b) If potassium manganate(VII) and very dilute hydrochloric acid are mixed, there is no visible reaction. Suggest why there is no visible reaction in this case.

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

........................................................................................................................[1]

[Total 7 marks]

68. Phenol, C6H5OH, is a powerful disinfectant and antiseptic.

Phenol is a weak Brønsted–Lowry acid.

C6H5OH(aq) H+(aq) + C6H5O−(aq) Ka = 1.3 × 10–10 mol dm–3

Define the following terms:

(i) A Brønsted–Lowry acid,

........................................................................................................................[1]

(ii) A weak acid.

........................................................................................................................[1]

[Total 2 marks]

69. When phenol is mixed with aqueous sodium hydroxide, an acid–base reaction takes place.

C6H5OH(aq) + OH–(aq) C6H5O–(aq) + H2O(l)

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

In the available spaces,

• label one conjugate acid–base pair as acid 1 and base 1,

• label the other conjugate acid–base pair as acid 2 and base 2.[Total 1 mark]

70. A solution of phenol in water has a concentration of 4.7 g dm–3.

(i) Write an expression for the acid dissociation constant, Ka, of phenol.

[1]

(ii) Calculate the pH of this solution of phenol.

[5]

[Total 6 marks]

71. As part of an investigation, a student needed to prepare a buffer solution with a pH value of 8.71. From the Ka value of phenol, the student thought that a mixture of phenol and sodium phenoxide could be used to prepare this buffer solution.

The student decided to use a 0.200 mol dm–3 solution of phenol, mixed with an equal volume of sodium phenoxide.

Use your knowledge of buffer solutions to determine the concentration of sodium phenoxide solution that the student would need to mix with the 0.200 mol dm–3 phenol solution.

[Total 3 marks]

72. Syngas is a mixture of carbon monoxide and hydrogen gases, used as a feedstock for the manufacture of methanol.

A dynamic equilibrium was set up between carbon monoxide, CO, hydrogen, H2, and methanol, CH3OH, in a 2.0 dm3 sealed vessel.

The equilibrium is shown below.

CO(g) + 2H2(g) CH3OH(g)

The number of moles of each component at equilibrium is shown below

component CO(g) H2(g) CH3OH(g)

number of moles at equilibrium 6.20 × 10–3 4.80 × 10–2 5.20 × 10–5

(a) State two features of a system that is in dynamic equilibrium.

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

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

........................................................................................................................[2]

(b) (i) Write an expression for Kc for this equilibrium system.

[1]

(ii) Calculate Kc for this equilibrium. State the units.

Kc = ……………………... units:…………..…..[4]

(c) The pressure was increased whilst keeping the temperature constant. The mixture was left to reach equilibrium.

The equilibrium position above shifted to the right.

(i) Explain why the equilibrium position shifted to the right.

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

...............................................................................................................[1]

(ii) What is the effect, if any, on the value of Kc?

...............................................................................................................[1]

(d) The temperature was increased whilst keeping the pressure constant. The mixture was left to reach equilibrium.

The value of Kc for the equilibrium above decreased.

(i) Explain what happened to the equilibrium position in the equilibrium.

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

...............................................................................................................[1]

(ii) Deduce the sign of the enthalpy change for the forward reaction shown in the equilibrium above.


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

...............................................................................................................[1]

(e) Methanol can be used as an additive to petrol.

(i) Write an equation for the complete combustion of methanol, CH3OH.

...............................................................................................................[1]

(ii) Suggest why methanol is added to petrol.

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

...............................................................................................................[1]

[Total 13 marks]

73. Nitrogen monoxide reacts with hydrogen at 500 °C as in the equation below.

2NO(g) + 2H2(g) → N2(g) + 2H2O(g)

A series of experiments was carried out to investigate the kinetics of this reaction. The results are shown in the table below.

experiment [NO]/ mol dm–3

[H2]/ mol dm–3

initial rate/ mol dm–3 s–1

1 0.10 0.20 2.6

2 0.10 0.50 6.5

3 0.30 0.50 58.5

In this question, one mark is available for the quality of spelling, punctuation and grammar.

(i) For each reactant, deduce the order of reaction. Show your reasoning.

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

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

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

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

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

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

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

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

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

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

........................................................................................................................[4]


(ii) Deduce the rate equation for this reaction.

........................................................................................................................[1]

(iii) Calculate the rate constant, k, for this reaction. State the units for k.

k = .................................................... units ....................................................[3]

[Total 9 marks]

74. Nitrogen monoxide, NO, is involved in formation of ozone at low levels and the breakdown of ozone at high levels.

(i) In the lower atmosphere, NO is produced by combustion in car engines. Ozone is then formed following the series of reactions shown below.

NO(g) + 1/2O2(g) → NO2(g)

NO2(g) → NO(g) + O(g)

O2(g) + O(g) → O3(g)

Write the overall equation for this reaction sequence.

Identify the catalyst and justify your answer.

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

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

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

........................................................................................................................[3]

(ii) In the upper atmosphere, NO removes O3 by the following reaction mechanism.

NO(g) + O3(g) → NO2(g) + O2(g) slow

O(g) + NO2(g) → NO(g) + O2(g) fast

Suggest the rate equation for this process. Explain your reasoning.

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

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

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

........................................................................................................................[2]

[Total 5 marks]

75. When heated, phosphorus pentachloride, PCl5, dissociates.

PCl5(g) PCl3(g) + Cl2(g)

A chemist placed a mixture of the three gases into a container. The initial concentration of each gas was the same: 0.30 mol dm–3. The container was left until equilibrium had been reached.

Under these conditions, Kc = 0.245 mol dm–3.

(a) Write an expression for Kc for this equilibrium.

[1]

(b) Use the value of Kc for this equilibrium to deduce whether the concentration of each gas increases, decreases or stays the same as the mixture approaches equilibrium.

(i) Show your answer by placing a tick in the appropriate cells in the table below.

initial concentration/ mol dm–3

greater than0.30 mol dm–3

less than0.30 mol dm–3

equal to0.30 mol dm–3

PCl5 0.30

PCl3 0.30

Cl2 0.30

[1]

(ii) Explain your deduction.

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

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

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

...............................................................................................................[1]

(c) The chemist compressed the equilibrium mixture at constant temperature and

allowed it to reach equilibrium under these new conditions.

(i) Explain what happens to the value of Kc.

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

...............................................................................................................[1]

(ii) Explain what happened to the composition of the equilibrium mixture.

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

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

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

...............................................................................................................[2]

(d) The chemist heated the equilibrium mixture and the equilibrium moved to the left.

(i) Explain what happens to the value of Kc.

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

...............................................................................................................[1]

(ii) Explain what additional information this observation reveals about the reaction.

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

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

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

...............................................................................................................[2]

[Total 9 marks]

76. In sewage plants, biological activity can be reduced by increasing the pH of the water. This is achieved by adding small amounts of solid calcium hydroxide, Ca(OH)2, to the sewage water.

In all parts of this question, assume that measurements have been made at 25 °C.

(a) The pH of aqueous solutions is determined by Kw.

Kw has a value of 1.0 × 10–14 mol2 dm–6 at 25 °C.

(i) What name is given to Kw?

...............................................................................................................[1]

(ii) Write the expression for Kw.

...............................................................................................................[1]

(b) A chemist checked the concentration of aqueous calcium hydroxide, Ca(OH)2, in the sewage water by titration with 5.00 × 10–3 mol dm–3 hydrochloric acid.

Ca(OH)2(aq) + 2HCl(aq) → CaCl2(aq) + 2H2O(l)

The chemist titrated 25.0 cm3 of the sewage water with 21.35 cm3 of HCl to reach the endpoint of the titration.

Calculate the concentration, in mol dm–3, of the calcium hydroxide in the sewage water.

concentration = .......................................... mol dm–3

[3]

(c) The chemist analysed a sample of water from another part of the sewage works and he found that the calcium hydroxide concentration was 2.7 × 10–3 mol dm–3.

When solid calcium hydroxide dissolves in water, its ions completely dissociate.

Ca(OH)2(s) → Ca2+(aq) + 2OH–(aq)

Calculate the pH of this sample.

[3]

(d) After further treatment, the water could be used for drinking. In the drinking water produced, the OH– concentration was 100 times greater than the H+ concentration.

What was the pH of this drinking water?

[1]

[Total 9 marks]

77. ‘Superphosphate’ fertilisers contain calcium dihydrogenphosphate, Ca(H2PO4)2. This compound is one of the world's most important fertilisers. When dissolved in water, Ca(H2PO4)2 dissociates forming H2PO4

– ions which are easily taken up by plants.

(a) Calcium dihydrogenphosphate, Ca(H2PO4)2, is produced by treating rock phosphate, containing Ca3(PO4)2, with sulphuric acid, H2SO4.

Write a balanced equation for this reaction.

........................................................................................................................[1]

(b) Aqueous H2PO4– ions can act as a weak acid.

Write an equation to represent the dissociation of the H2PO4– ion.

........................................................................................................................[1]

(c) The H2PO4– ion can act as either an acid or a base.

(i) State the formula of the conjugate base of H2PO4–.

...............................................................................................................[1]

(ii) State the formula of the conjugate acid of H2PO4–.

...............................................................................................................[1]

(iii) A solution of calcium dihydrogenphosphate, Ca(H2PO4)2, in water acts as a buffer solution.

Suggest, with the aid of equations, how this buffering action takes place.

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

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

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

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

...............................................................................................................[3]

[Total 7 marks]

78. In order to obtain full marks in this question, you must show all your working clearly.

In its reactions, sulphuric acid, H2SO4, can behave as an acid, an oxidising agent and as a dehydrating agent.

The displayed formula of pure sulphuric acid is shown below.

Dilute sulphuric acid takes part in the typical acid reactions, reacting with metals, carbonates and bases.

Write balanced equations for the reaction of sulphuric acid with

a metal, ...................................................................................................................

a carbonate, ............................................................................................................

a base. ....................................................................................................................[Total 3 marks]

79. 1, 2-Dibromoethane, C2H4Br2, reacts with potassium iodide as shown in the equation below.

C2H4Br2 + 3KI → C2H4 + 2KBr + Kl3

A series of experiments was carried out to investigate the kinetics of this reaction.

(a) In a first experiment the concentration of C2H4Br2 was measured during the course of the reaction and a concentration-time graph was plotted. The reaction was shown to be first order with respect to C2H4Br2.

(i) On the axes below, sketch a graph to show how [C2H4Br2] changed during the course of the reaction.

[2]

(ii) Show on the graph how you would measure the initial rate of the reaction.[1]

(iii) How would you use the graph to show that the reaction is first order with respect to C2H4Br2?

................................................................................................................[1]

(iv) The experiment was repeated using different initial concentrations of C2H4Br2.

Using the axes below, sketch a graph to show how the initial rate of the reaction changes with different concentrations of C2H4Br2.

[1]

(b) In a second experiment, the initial concentration of KI was varied and the initial rate was measured. The results are shown in the table below.

experiment [C2H4Br2]/mol dm–3

[KI]/mol dm–3

initial rate/mol dm–3s–1

1 0.50 0.18 0.0272 0.50 0.72 0.108

Deduce the order of reaction with respect to KI. Show your reasoning.

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

.........................................................................................................................[2]

(c) (i) Construct the rate equation for the reaction.

................................................................................................................[1]

(ii) Calculate the rate constant, k, for this reaction. State the units for k.

k = ............................ units ..................................[3]

[Total 11 marks]

80. Some ammonia plants are run at 200–300 atm and 500 °C, with an iron catalyst.

(a) The hydrogen for the plants is obtained by reacting methane with steam.

Construct a possible equation for this reaction.

.........................................................................................................................[1]

(b) Nitrogen gas and hydrogen gas produce ammonia gas as shown below.

N2(g) + 3H2(g) 2NH3(g) ΔH = –92 kJ mol–1

(i) Write the expression for Kc for this equilibrium.

[1]

(ii) At 500 °C, Kc = 8.00 x 10–2 dm6 mol–2.

At equilibrium, the concentration of N2 is 1.20moldm–3 and the concentration of H2 is 2.00moldm–3.

Calculate the equilibrium concentration of ammonia under these conditions.

equilibrium concentration of NH3 = ........................................ moldm–3

[3]

(c) In this question one mark is available for the quality of the use and organisation of scientific terms.

Discuss the advantages and disadvantages of running this reaction

• at a pressure of 200–300 atm;

• at a temperature of 500°C;

• with an iron catalyst.[6]


[Total 12 marks]

81. This question looks at two acids:

• methanoic acid, HCOOH, a weak organic acid;

• nitric acid, HNO3, a strong acid which can also act as a powerful oxidising agent.

Methanoic acid is a weak BrØnsted-Lowry acid.

Explain what is meant by a weak BrØnsted-Lowry acid.

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

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

..................................................................................................................................[Total 2 marks]

82. Calculate the pH of a 0.025 mol dm–3 solution of methanoic acid. Show your working.

For HCOOH, Ka = 1.58 x l0–4mol dm–3.

pH = ............................[Total 3 marks]

83. Methanoic acid is a component of a buffer solution used in shampoos. The buffer solution can be made by mixing methanoic acid with another chemical.

(i) State what is meant by a buffer solution.

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

.........................................................................................................................[1]

(ii) Suggest a chemical that could be added to methanoic acid to prepare a buffer solution. Explain your answer.

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

.........................................................................................................................[2]

(iii) What factors determine the pH of a buffer solution?

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

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

.........................................................................................................................[2]

[Total 5 marks]

84. Nitric acid, HN03, is sold by a chemical supplier as a 65% solution, by mass. As supplied, each cubic decimetre of this nitric acid has a mass of 1400g.

Calculate the pH of this solution.

pH = ....................................[Total 3 marks]

85. When dilute, nitric acid behaves as a typical acid.

Write an equation for the reaction of nitric acid with limestone.

..................................................................................................................................[Total 2 marks]

86. When nitric acid is added to methanoic acid, the acid-base equilibrium below is set up.

HNO3 + HCOOH NO3– + HCOOH2

+

Use this equilibrium to explain what is meant by the term conjugate acid-base pairs.

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

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

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

..................................................................................................................................[Total 3 marks]

87. A student analysed an unsaturated carboxylic acid, A, using a titration procedure.

The student dissolved 2.580 g of the compound in water and made the solution up to 250.0cm3. The student titrated 25.0 cm3 of this solution with 0.1263mol dm–3 NaOH. The volume of NaOH(aq) required to reach the end point was 23.75cm3.

Each molecule of A has one acidic hydrogen atom and A behaves as a monoprotic (or monobasic) acid.

• Calculate the molar mass of the unsaturated carboxylic acid.

• Determine the molecular formula and possible displayed or skeletal formulae of the carboxylic acid.

[Total 8 marks]

88. Methanoic acid, HCOOH, is a weak organic acid which occurs naturally in ants and stinging nettles.

(a) Use an equation for the dissociation of methanoic acid to show what is meant by a weak acid.

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

........................................................................................................................[1]

(b) A 1.50 × 10–2 mol dm–3 solution of HCOOH has [H+] = 1.55 × 10–3 mol dm–3.

(i) Calculate the pH of this solution and give one reason why the pH scale is a more convenient measurement for measuring acid concentrations than [H+].

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

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

...............................................................................................................[2]

(ii) Write the expression for Ka for methanoic acid.

[1]

(iii) Calculate the values of Ka and pKa for methanoic acid.

[3]

(iv) Estimate the percentage of HCOOH molecules that have dissociated in this aqueous solution of methanoic acid.

[1]

[Total 8 marks]

89. A student titrated the 1.50 × 10–2 mol dm–3 methanoic acid with aqueous sodium hydroxide.A 25.00 cm3 sample of the HCOOH(aq) was placed in a conical flask and the NaOH(aq) was added from a burette until the pH no longer changed.

(i) Write a balanced equation for the reaction between HCOOH(aq) and NaOH(aq).

........................................................................................................................[1]

(ii) Part of the pH curve for this titration is shown below.

Calculate the concentration, in mol dm–3, of the aqueous sodium hydroxide.

concentration = ......................mol dm–3

[3]

(iii) Calculate the pH of the aqueous sodium hydroxide.Kw = 1.00 × 10–14 mol dm–3

pH = .......................................[2]

(iv) The pH ranges in which colour changes for three acid-base indicators are shown below.

indicator pH range

metacresol purple2,4,6-trinitrotoluene

ethyl orange

7.4 – 9.011.5 – 13.03.4 – 4.8

Explain which of the three indicators is suitable for this titration.

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

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

........................................................................................................................[2]

[Total 8 marks]

90. The preparation of hydrogen iodide, HI(g), from hydrogen and iodine gases is a reversible reaction which reaches equilibrium at constant temperature.

H2(g) + I2(g) 2HI(g)

(a) Write the expression for Kc for this equilibrium.

[1]

(b) A student mixed together 0.30 mol H2(g) with 0.20 mol I2(g) and the mixture was allowed to reach equilibrium. At equilibrium, 0.14 mol H2(g) was present.

(i) Complete the table below to show the amount of each component in the equilibrium mixture.

component H2(g) I2(g) HI(g)

initial amount / mol 0.30 0.20 0

equilibrium amount / mol

[2]

(ii) Calculate Kc to an appropriate number of significant figures. State the units, if any.

Kc = ...........................................

units, if any ...........................................................................................[3]

(c) The student compressed the equilibrium mixture so that its volume was reduced. The temperature was kept constant.

Comment on the value of Kc and the composition of the equilibrium mixture under these new conditions.

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

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

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

........................................................................................................................[2]

[Total 8 marks]

91. Hydroiodic acid, HI(aq), is a strong acid that is an aqueous solution of hydrogen iodide.In the laboratory, hydroiodic acid can be prepared by the method below.

A mixture of 480 g of iodine and 600 cm3 of water was put into a flask. The mixture was stirred and hydrogen sulphide gas, H2S(g), was bubbled through for several hours.

The mixture became yellow as sulphur separated out. The sulphur was filtered off and the solution was purified by fractional distillation. A fraction of HI(aq) was collected containing 440 g of HI in a total volume of 750 cm3.

(i) Construct a balanced equation, with state symbols, for the preparation of hydroiodic acid.

...............................................................................................................[2]

(ii) Determine the percentage yield of hydroiodic acid.

[3]

(iii) Calculate the pH of the hydroiodic acid fraction.

[2]

[Total 7 marks]


Propanone reacts with iodine in the presence of dilute hydrochloric acid.

A student carried out an investigation into the kinetics of this reaction.

He measured how the concentration of propanone changes with time. He also investigated how different concentrations of iodine and hydrochloric acid affect the initial rate of the reaction.

The graph and results are shown below.

[CH3COCH3]/ mol dm–3

[I2]/ mol dm–3

[H+]/ mol dm–3

initial rate/ mol dm–3 s–1

1.5 ×10–3 0.0300 0.0200 2.1 ×10–9

1.5 ×10–3 0.0300 0.0400 4.2 ×10–9

1.5 ×10–3 0.0600 0.0400 4.2 ×10–9

The overall equation for the reaction is given below.

CH3COCH3 + I2 → CH3COCH2I + HI

This is a multi-step reaction.

• What conclusions can be drawn about the kinetics of this reaction from the student’s investigation? Justify your reasoning.

• Calculate the rate constant for this reaction, including units.

• Suggest the equations for a possible two-step mechanism for this reaction. Label the rate-determining step and explain your reasoning.


[Total 14 marks]

93. This question looks at different compounds used in medicine.

(a) Nitrous oxide, N2O, is the gas used as a general anaesthetic.

(i) What is the oxidation number of nitrogen in nitrous oxide?

...............................................................................................................[1]

(ii) Suggest a ‘dot-and-cross’ diagram for nitrous oxide. Show outer electrons only.The sequence of atoms in a nitrous oxide molecule is N N O.

[1]

(b) The structure of the painkiller ibuprofen is shown below.

(i) Determine the molecular formula of ibuprofen.

[1]

(ii) Suggest a chemical that would react with a solution of ibuprofen to produce a gas.Name the gas produced and write a balanced equation for the reaction.

chemical ...............................................................................................

gas ........................................................................................................

equation

[2]

(c) Lidocaine, C13H20N2O2, is used as a local anaesthetic in dentistry. Lidocaine is administered by syringe as a solution containing 100 mg in 5.00 cm3.

Calculate the concentration, in mol dm–3, of lidocaine in the syringe.

concentration = ......................mol dm–3

[3]

(d) Eugenol is used as a painkiller in dentistry. It is an organic compound of C, Hand O.

A sample of 1.394 g of eugenol was analysed by burning in oxygen to form 3.74 g of CO2 and 0.918 g of H2O. The relative molecular mass of eugenol was shown to be 164 using a mass spectrometer.

Calculate the molecular formula of eugenol.

[5]

[Total 13 marks]

94. Nitrogen dioxide is one of the major pollutants in air, formed by reaction of nitrogen monoxide with oxygen.

2NO(g) + O2(g) → 2NO2(g)

(a) What is meant by the rate of reaction?

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

........................................................................................................................[1]

(b) A series of experiments was carried out to investigate the kinetics of this reaction. The results are shown in the table below.

Experiment[O2]

/ mol dm–3[NO]

/ mol dm–3initial rate

/ mol dm–3 s–1

1 0.00100 0.00100 7.10

2 0.00400 0.00100 28.4

3 0.00400 0.00300 256

(i) For each reactant, deduce the order of reaction. Show your reasoning.

O2(g) .....................................................................................................

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

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

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

NO(g) ....................................................................................................

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

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

...............................................................................................................[4]

(ii) Deduce the rate equation for this reaction.

...............................................................................................................[1]

(iii) Calculate the rate constant, k, for this reaction. State the units for k.

k = ................................... units ...................................[2]

[Total 8 marks]

95. Nitrogen dioxide reacts with carbon monoxide emitted from car exhausts in the following reaction.

NO2 + CO → NO + CO2

The rate equation for this reaction is rate = k[NO2]2.

This is a multi-step reaction. The first step is the rate-determining step.

(i) What is meant by the rate-determining step?

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

........................................................................................................................[1]

(ii) Suggest a two-step reaction mechanism for this reaction that is consistent with the kinetic data and the overall reaction.

[2]

[Total 3 marks]

96. The Ka values for three acids are shown in the table below.

acid Ka / mol dm–3

ethanoic acid CH3COOH 1.70 ×10–5

phenol C6H5OH 1.28 ×10–10

sulphurous acid H2SO3 1.50 ×10–2

(a) What information is provided by Ka values?

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

........................................................................................................................[1]

(b) When sulphurous acid and ethanoic acid are mixed together, an acid-base reaction takes place.

H2SO3(aq) + CH3COOH(aq) HSO3–(aq) + CH3COOH2

+(aq)

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

(i) In the spaces above

• label one conjugate acid-base pair as acid 1 and base 1,• label the other conjugate acid-base pair as acid 2 and base 2.

[2]

(ii) Predict and explain the acid-base reaction that would take place if ethanoic acid were mixed with phenol. Include an equation in your answer.

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

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

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

...............................................................................................................[2]

(c) The pH value of 0.0450 mol dm–3 hydrochloric acid is different from that of 0.0450 mol dm–3 ethanoic acid.

Calculate the pH values of these two acids. Show all your working.

[5]

[Total 10 marks]

97. An excess of magnesium was added to 100 cm3 of 0.0450 mol dm–3 hydrochloric acid.The same mass of magnesium was added to 100 cm3 of 0.0450 mol dm–3 ethanoic acid.

Both reactions produced 54 cm3 of hydrogen gas, measured at room temperature and pressure, but the reaction with ethanoic acid took much longer to produce this gas volume.

Explain why the reactions produced the same volume of a gas but at different rates.

Use equations in your answer.

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

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

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

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

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

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

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

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

.................................................................................................................................[Total 4 marks]

98. Chocolate mousse contains gelatine and a compound to promote fast setting of the mousse.

Compound A is such a setting agent. It has two acidic hydrogen atoms per molecule and is one of the six acids listed below.

oxalic acid HOOCCOOH

malonic acid HOOCCH2COOH

succinic acid HOOC(CH2)2COOH

glutaric acid HOOC(CH2)3COOH

adipic acid HOOC(CH2)4COOH

pimelic acid HOOC(CH2)5COOH

The student analysed a sample of compound A by titration.

The student dissolved 2.82 g of compound A in water and made the solution up to 250 cm3 in a volumetric flask. He titrated 25.0 cm3 of this solution with 0.175 mol dm–3 NaOH.

22.05 cm3 of NaOH were required for complete neutralisation.

Use the results of the student’s analysis to identify compound A from the list above.

Show all of your working.

[Total 5 marks]

99. In the UK, almost all the sulphuric acid, H2SO4, is manufactured by the Contact process.One stage in the Contact process involves the reaction between sulphur dioxide and oxygen.

2SO2(g) + O2(g) 2SO3(g)

The table below shows values of the equilibrium constant, Kp, for this equilibrium at different temperatures.

temperature / °C Kp / kPa–1

25 4.0 × 1022

200 2.5 × 108

800 1.3 × 10–3

(a) Write an expression for the equilibrium constant, Kp, of this reaction.

[2]

(b) In this question, one mark is available for the quality and use of scientific terms.

• The conversion of sulphur dioxide and oxygen into sulphur trioxide is carried out at slightly above atmospheric pressure. Comment on this statement.

• Explain what happens to the equilibrium amounts of SO2, O2 and SO3 as temperature increases at constant pressure.

• Deduce the sign of ∆H for the forward reaction in the equilibrium. Explain your reasoning carefully.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

........................................................................................................................[6]


(c) An equilibrium is set up for the SO2, O2, SO3 equilibrium at 400 °C.

At this temperature

• the equilibrium partial pressure of SO2 is 10 kPa

• the equilibrium partial pressure of O2 is 50 kPa

• Kp = 3.0 × 102 kPa–1.

Calculate the equilibrium partial pressure of SO3 at 400 °C. Hence determine the percentage of SO3 in the equilibrium mixture at this temperature.

answer ..................................%[3]

(d) In the UK, almost all the sulphuric acid manufactured uses sulphur as a starting material for SO2 production. In some countries, metal ores such as zinc sulphide, ZnS, are used instead to form SO2 by heating with air.

(i) Construct a balanced equation to show the reaction that takes place when zinc sulphide is heated in air.

...............................................................................................................[2]

(ii) Suggest why countries may find it more economic to manufacture sulphuric acid from zinc sulphide.

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

...............................................................................................................[1]

[Total 15 marks]

100. One cause of low-level smog is the reaction of ozone, O3, with ethene. The smog contains methanal, CH2O(g), and the equation for its production is shown below.

O3(g) + C2H4(g) → 2CH2O(g) + O2(g) equation 1

(a) The rate of the reaction doubles when the initial concentration of either O3(g) or C2H4(g) is doubled.

(i) What is the order of reaction with respect to

O3 .............................

C2H4? .......................[1]

(ii) What is the overall order of the reaction?

..............................................................[1]

(iii) Write the rate equation for this reaction.

...............................................................................................................[1]

(b) For an initial concentration of ozone of 0.50 × 10–7 mol dm–3 and one of ethene of 1.0 × 10–8 mol dm–3, the initial rate of methanal formation was1.0 × 10–12 mol dm–3 s–1.

(i) How could the initial rate of methanal formation be measured from a concentration/time graph?

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

...............................................................................................................[2]

(ii) Calculate the value of the rate constant and state the units.

rate constant =.......................... units....................................[3]

(iii) The initial rate of methanal formation is different from that of oxygen formation in equation 1.

Explain why.

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

...............................................................................................................[1]

(iv) The experiment was repeated but at a higher temperature. What would be the effect of this change on the rate and the rate constant of the reaction?

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

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

...............................................................................................................[2]

[Total 11 marks]

101. In the stratosphere, ozone forms when oxygen free radicals react with oxygen molecules.

O2 + O → O3

The oxygen free radicals are initially formed as diradicals when oxygen gas, O2, is dissociated by strong ultraviolet radiation,

O2(g) → 2O(g)

(i) Suggest why oxygen free radicals, O, are often called diradicals.

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

........................................................................................................................[1]

(ii) Draw a ‘dot-and-cross’ diagram of an ozone molecule. Show outer electrons only.

[2]

(iii) Chlorine free radicals formed from CFCs deplete the ozone layer in a chain reaction.

Typically, 1 g of chlorine free radicals destroys 150 kg of ozone during the atmospheric lifetime of the chlorine free radical (one to two years).

Calculate how many ozone molecules are destroyed in this chain reaction by a single chlorine free radical before the free radical is destroyed.

answer........................................[3]

[Total 6 marks]

102. Phenol, C6H5OH, is a powerful disinfectant and antiseptic. Phenol is a weak Brønsted-Lowry acid.

What is meant by the following terms;

(i) a Brønsted-Lowry acid;

........................................................................................................................[1]

(ii) a weak acid?

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

........................................................................................................................[1]

[Total 2 marks]

103. When phenol is mixed with aqueous sodium hydroxide, an acid-base reaction takes place.

C6H5OH(aq) + OH–(aq) C6H5O–(aq) + H2O(l)

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

In the spaces above,

• label one conjugate acid-base pair as acid 1 and base 1,• label the other conjugate acid-base pair as acid 2 and base 2.

[Total 2 marks]

104. A solution of phenol in water has a concentration of 38 g dm–3.The acid dissociation constant, Ka, of phenol is 1.3 × 10–10 mol dm–3.

(i) Write an expression for the acid dissociation constant, Ka, of phenol.

[1]

(ii) Calculate the pH of this solution.

answer........................................[5]

[Total 6 marks]

105. Hexylresorcinol is an antiseptic used in solutions for cleansing wounds and in mouthwashes and throat lozenges.

The structure of hexylresorcinol is shown below.

Identify a compound that could be added to hexylresorcinol to make a buffer solution.Explain your answer.

[Total 2 marks]

106. Compound B is an organic base. A student analysed this base by the procedure below.

He first prepared a solution of B by dissolving 4.32 g of B in water and making the solution up to 250 cm3. The student then carried out a titration in which 25.00 cm3 of this solution of B were neutralised by exactly 23.20 cm3 of 0.200 mol dm–3 HCl.

1 mole of B reacts with 1 mole of HCl.

Use this information to calculate the molar mass of base B and suggest its identity.

[Total 6 marks]

107. The decomposition of dinitrogen pentoxide, N2O5, at 45 °C was investigated. The reaction that takes place is shown below.

2N2O5 → 4NO2 + O2

In an experiment, N2O5 with a concentration of 0.60 mol dm–3 was decomposed at45 °C.

At this temperature, the reaction has a constant half-life of 1200 s.

(i) How can you tell that this reaction is first order with respect to N2O5?

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

........................................................................................................................[1]

(ii) Write down an expression for the rate equation of this decomposition.

........................................................................................................................[1]

(iii) Complete the graph below to show how the [N2O5] changes over the first 3600 s of the reaction.

[2]

(iv) The rate of this reaction can be determined from this graph.

Show on the graph how the rate can be measured after 1200 s.[1]

(v) The rate can also be calculated from the rate equation. The rate constant for this reaction is 6.2 × 10–4 s–1.

Calculate the initial rate of this reaction. State the units.

rate =………….…..……. units………..….………..[2]

[Total 7 marks]

108. A student investigated the hydration of 2-methylpropene, (CH3)2C=CH2, with dilute aqueous acid to form 2-methylpropan-2-ol, (CH3)3COH.

The following mechanism has been proposed for this hydration.

step 1 (CH3)2C=CH2 + H+(aq) → (CH3)3C+ rate determining step

step 2 (CH3)3C+ + H2O → (CH3)3COH + H+(aq)

(i) Step 1 is the rate-determining step for this hydration.

What is meant by the term rate-determining step?

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(ii) Write a balanced equation for the overall hydration reaction.

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(iii) Suggest the role of H+(aq) in this mechanism. Explain your reason.

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(iv) Use the mechanism above to suggest the rate equation for this hydration.

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[Total 5 marks]

109. Methanol, CH3OH(g), is manufactured from carbon monoxide and hydrogen in an equilibrium reaction.

CO(g) + 2H2(g) CH3OH(g) ∆H = –91 kJ mol–1

(a) In this question, one mark is available for the quality of use and organisation of scientific terms.

Explain the advantages and disadvantages of running this reaction

• at a high pressure,

• at a high temperature.

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(b) This equilibrium reaction is normally carried out at 10MPa pressure and 550 K, and starting with a 1 : 2 CO : H2 mixture. At equilibrium, only 10% of the CO has reacted.

(i) Deduce the equilibrium amounts, mole fractions and partial pressures of CO, H2 and CH3OH present at equilibrium. Write your answers in the table below.

Assume that you have started with a mixture of 1.0 mol CO and 2.0 mol H2.

CO H2 CH3OH

initial amount /mol 1.0 2.0 0.0

equilibrium amount /mol 0.9

mole fraction atequilibrium

partial pressure atequilibrium /MPa

[4]

(ii) Write the expression for Kp for this equilibrium.

[2]

(iii) The CO : H2 ratio in the starting mixture was changed from 1 : 2 to 1 : 3 and the mixture was allowed to reach equilibrium at the same temperature and pressure.

Explain, in terms of Kp, the effect of this change on the equilibrium yield of CH3OH.

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(iv) In another experiment, the equilibrium partial pressures were:

CO, 3.70 MPa; H2, 5.10 MPa; CH3OH, 0.261 MPa.

Calculate the value of Kp for this equilibrium. Express your answer to an appropriate number of significant figures. State the units of Kp.

Kp = ............................. units.............................[2]

(c) In the UK, the annual production of methanol is 500 000 tonnes. Methanol has many uses in fuels as a reliable and low pollution form of energy.

Suggest an equation for the combustion of methanol.

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[Total 18 marks]

110. A student carried out an investigation with aqueous solutions of nitric acid, sodium

hydroxide, ethanoic acid and water.

Nitric acid, HNO3, is a strong Brønsted-Lowry acid.

(i) Explain what is meant by a strong acid and a Brønsted-Lowry acid.

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(ii) What is the conjugate base formed from HNO3?

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[Total 3 marks]

111. A student carried out an investigation with aqueous solutions of nitric acid, sodium hydroxide, ethanoic acid and water.

The student diluted 0.015 mol dm–3 nitric acid with an equal volume of water and measured the pH of the diluted acid at 25 °C.

(i) Calculate the pH of 0.015 mol dm–3 nitric acid.

[2]

(ii) Calculate the pH of the diluted acid.

[1]

[Total 3 marks]

112. A student measured the pH of a solution of sodium hydroxide as 13.54 at 25 °C.

Kw = 1.0 × 10–14 mol2 dm–6 at 25 °C.

(i) Write down an expression for the ionic product, Kw, for water.

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(ii) Calculate the concentration, in mol dm–3, of this solution of sodium hydroxide.

[2]

[Total 3 marks]

113. A student prepared two solutions.

• Solution A was made by mixing together 25 cm3 0.010 mol dm–3 aqueous sodium hydroxide with 50 cm3 0.010 mol dm–3 ethanoic acid, CH3COOH. Solution A is a buffer solution.

• Solution B was made by mixing together 25 cm3 0.020 mol dm–3 aqueous sodium hydroxide with 50 cm3 0.010 mol dm–3 ethanoic acid, CH3COOH. Solution B is not a buffer solution.

(i) What is meant by a buffer solution?

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(ii) Explain why Solution A is a buffer solution whereas Solution B is not.

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[Total 5 marks]

114. A student measured the pH of water as 7.0 at 25 °C. The student then warmed the

water to 40 °C and measured the pH as 6.7.

What do these results tell you about the tendency of water to ionise as it gets warmer?Explain your reasoning in terms of equilibrium.

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1. one cause of low-level smog is the reaction of ozone, o

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