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) + 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 1 2 3 [O3(g)] / 10 mol dm 0.5 2.0 4.07 3

[C2H4(g)] / 108

mol dm 1.0 1.0 2.0

3

initial rate 12 3 1 / 10 mol dm s 1.0 4.0 16.0

(i)

Analyse and interpret the results to deduce the order of reaction of each reactant and the rate equation. Explain your reasoning. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[5]

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(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. Explain your reasoning.

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) + O2(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. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. .................................................................................................................................[Total 3 marks]

3.

This question looks at the chemistry of transition elements. (a) (ii) (i) Explain what is meant by the terms transition element, complex ion and ligand, 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]

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

5.

Mercury forms two ions, Hg2 of mercury in these ions.

2+

and Hg . The table shows the electronic configuration

2+

ion Hg2 Hg2+

electronic configuration [Xe]4f 5d 6s [Xe]4f 5d14 10 14 10 1

2+

Use the electronic configurations to explain why mercury is not a transition element. ................................................................................................................................. .................................................................................................................................[Total 1 mark]

6.

A sample of iron is heated with a stream of dry hydrogen chloride. A different chloride 2+ of iron is formed that contains the Fe 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 Fe . 1s 2s 2p .......................................................................................................[1]2 2 6 2+

(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 Fe (aq). State what you would observe. ........................................................................................................................ Write an ionic equation, with state symbols, for the reaction. ........................................................................................................................[2] [Total 5 marks]

2+

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 conical flask. Stage 2 The sample is reacted with a known excess amount of Fe with 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 potassium manganate(VII) in acidic conditions to find the amount of unreacted 2+ Fe .2+

acidified

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(i)

The reduction half-equation for manganese(IV) oxide in the presence of dilute acid is shown below. MnO2(s) + 4H (aq) + 2e Mn (aq) + 2H2O(l) Construct the balanced equation for the redox reaction between Fe (aq), + MnO2(s) and H (aq). ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[1]2+ + 2+

(ii)

In Stage 1 and Stage 2 a student uses a 0.504 g sample of impure MnO2 and 100 cm of 0.200 mol dm3 3

Fe .2+

2+

In Stage 4 the student determines that the amount of unreacted Fe 0.0123 mol. 1 mol of MnO2 reacts with 2 mol of Fe . Calculate the percentage purity of the impure sample of MnO2.2+

is

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 B C (a) = [Ru(H2O)6]3+

= [Ru(H2O)5Cl]

2+

= [Ru(H2O)4Cl2] (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]

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(b)

The complex ion [Ru(H2O)6] (i)

3+

can be converted into [Ru(H2O)5Cl] .

2+

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 Cu (aq) + 2e

2+

Cu(s) is +0.34 V.2+

A student measured the standard electrode potential of Cu (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 Cu (aq) ions in the solution by titration. 25.00 cm of the solution containing Cu ions were pipetted into a volumetric flask and 3 she made the volume up to 250.0 cm with distilled water. An excess of aqueous potassium iodide, KI, was added to 25.00 cm of the diluted solution. 3 The iodine formed was titrated against 0.100 mol dm sodium thiosulphate, Na2S2O3. The volume of Na2S2O3(aq) used was 23.20 cm .3 3 3 2+ 2+

The equations for the formation and titration of iodine are given below. 2Cu (aq) + 4I (aq) 2CuI(s) + I2(aq)2+

I2(aq) + 2S2O32(aq) 2I(aq) + S4O62(aq)

(i)

State how the student would identify the end point of the titration. ........................................................................................................................ ........................................................................................................................[1]

(ii)

Show that the concentration of the Cu (aq) ions was 0.93 mol dm .

2+

3

[4]

(iii)

Explain, in terms of chemical equilibrium, why the emf of this cell was less than the standard electrode potential. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[2] [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, Fe . 1s 2s 2p .......................................................................................................[1]2 2 6 3+

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(ii)

Explain, using electronic configuration, why iron is a transition element. ........................................................................................................................ ........................................................................................................................[1] [Total 2 marks]

11.

Iron forms several complex ions in which the oxidation state of iron is +3. One of these complex ions is [Fe(CN)6] . 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] 3

(ii)

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

3

[2] [Total 3 marks]

12.

Iron forms several complex ions in which the oxidation state of iron is +3. Excess aqueous sodium hydroxide is added to an aqueous solution containing Fe (aq). (i) Describe what you would see happen. ........................................................................................................................[1]3+

(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) 2

Fe2O3(s) + 10OH (aq) 2FeO4 (aq) + 5H2O(I) + 6e

Construct the redox equation for the reaction between chlorine, iron(III) oxide and hydroxide ions. ................................................................................................................................. ................................................................................................................................. .................................................................................................................................[Total 2 marks]

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14.

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

15.

An unusual compound of iron has been detected on the surface of the planet Mars. This compound contains the ferrate(VI) ion. Ferrate(VI) ions will decompose in acidic solution as shown in the equation below. 4FeO4 (aq) + 2OH (aq) 4Fe (aq) + 3O2(g) + 10H2O(l) Explain, in terms of oxidation numbers, why this decomposition involves both reduction and oxidation. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. .................................................................................................................................[Total 2 marks]2 + 3+

16.

An unusual compound of iron has been detected on the surface of the planet Mars. This compound contains the ferrate(VI) ion. 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. ........................................................................................................................[1] [Total 2 marks]

17.

Under certain conditions, VO can be converted into VO2 by reaction with KMnO4. The equation for the reaction is shown below. 5VO2+

2+

+

+ H2O + MnO4 5VO2 + Mn3 3

+

2+

+ 2H

+

What volume, in cm , of 0.0250 mol dm 20.0 cm of 0.100 mol dm3 3

KMnO4 would be required to convert+

VO

2+

into VO2 ?

volume of KMnO4 required = ...................... cm

3

[Total 3 marks]

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18.

The ethanedioate ion, C2O4 , 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. O C (a) O C O O

2

What do you understand by the term bidentate ligand? ........................................................................................................................ ........................................................................................................................[2]

(b)

The ethanedioate ion readily forms an octahedral complex ion with Cr . Show the structure and charge of this complex ion.

3+

[3] [Total 5 marks]

19.

The Cr

3+

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

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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, Fe (aq) ions are oxidised to Fe (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).2+ 3+

(i)

The reduction half equation for acidified dichromate(VI) ions, Cr2O7 , is as follows.2 + 3+ Cr2O7 (aq) + 14H (aq) + 6e 2Cr (aq) + 7H2O(l)

2

Construct the balanced equation for the redox reaction between Fe (aq), 2 + Cr2O7 (aq) and H (aq). .......................................................................................................................... .......................................................................................................................... ..........................................................................................................................[2]

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 cm of 0.0180 mol dm end-point. One mole of Cr2O72 3 3

Cr2O7

2

to reach the

reacts with 6 moles of Fe .

2+

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] (a)

2+

ions.

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

(i)

Describe the observations that would be made during the addition of the concentrated hydrochloric acid. ...............................................................................................................[1]

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(ii)

Describe the bonding within the complex ion, [CuCl4] . ............................................................................................................... ............................................................................................................... ...............................................................................................................[2]

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 2+ produce the complex ion [Cu(NH3)4(H2O)2] (aq). Describe the observations that would be made during the addition of concentrated aqueous ammonia. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[2] [Total 5 marks]

23.

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

H C2

H 0 9 . 5

u+

N 1 H

Explain why the HNH bond angle in the ammonia ligand is 109.5 rather than 107. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. .................................................................................................................................[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] . (i) What is the co-ordination number of Co2+ 2+

in this complex ion?

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

(ii)

Water is acting as a ligand. Explain the meaning of the term ligand. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[2] [Total 3 marks]

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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] (aq) + 4Cl (aq)2+

[CoCl4] (aq) + 6H2O(l)

2

(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) Co 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+

[2]

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(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. Cr2O7 ions oxidise I ions to I2 under acid conditions according to the following equation. Cr2O7 (aq) + 6I (aq) + 14H (aq)2 + 2

2Cr (aq) + 3I2(aq) + 7H2O(l)

3+

(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 2 concentration of a solution of Cr2O7 ions? In your answer state the method you would use state the reagents used show how you would use your results.

........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[4] [Total 5 marks]

28.

Copper and zinc are both d-block elements but only copper is a transition element. 2+ + Copper forms compounds containing Cu or Cu ions but zinc only forms compounds 2+ containing Zn ions. (a) Use the electronic configurations of Cu transition element and zinc is not.2+

and Zn

2+

to explain why copper is a

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

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(b)

Suggest two differences between compounds containing Zn

2+

and Cu

2+

ions.

........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[2] [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) Zn (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. + 2+

A student analyses a 1.23 g sample of brass using the method described. 3 The student collects 76.0 cm of hydrogen at room temperature and pressure. 3 1 mol of gas molecules occupies 24.0 dm 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]

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(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] Quality of Written Communication [1] [Total 10 marks]

33.

The edta (a)

4

ion forms complex ions with Ni (aq).2+

2+

Complete the electronic configuration of the Ni2 2 6

ion.

Is 2s 2p ........................................................................................................[1]

(b)

The edta O O O O

4

ion has the following structure. O

C

C

2H

H C2H

2

C C

N C C2H

C

2H

N H2

O O O

C C

(i)

Put a ring around two different types of atom in the edta ion that are 2+ capable of forming a dative covalent bond with the Ni ion.[2]

4

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(ii)

What feature of these atoms allows them to form a bond with Ni ? ...............................................................................................................[1] [Total 4 marks]

2+

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] + 2NH3 (i)x

[Pt(NH3)2Cl2] + 2Cl

y

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] exists in two isomeric forms. (i) Draw diagrams to show the structure of these isomers.

y

[2]

(ii)

What type of isomerism is this? ...............................................................................................................[1]

(iii)

One of the isomers of [Pt(NH3)2Cl2] is an important drug used in the treatment of cancer. How does this drug help in the treatment of cancer? ............................................................................................................... ............................................................................................................... ............................................................................................................... ...............................................................................................................[2] [Total 10 marks]

y

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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.3 3

(a) 25.0 cm of 0.100 mol dm ammonium vanadate(V) is completely reduced 2+ to V (aq) using zinc and aqueous sulphuric acid. The resulting solution is titrated 3 3 2+ with 0.0500 mol dm MnO4 (aq) and 30.0 cm is required to oxidise the V (aq) back to VO3 (aq). The half equation for acidified MnO4 acting as an oxidising agent is shown below. + 2+ MnO4 + 8H + 5e Mn + 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 V (aq) to VO3 (aq) by MnO4 (aq) under acid conditions.

2+

........................................................................................................................[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 2+ oxidation iron(II) ions, Fe , react with oxygen, O2, and hydrogen ions to make water and iron(III) ions, Fe .3+

(a)

Complete the electronic configuration for Fe3+ and use it to explain why iron is a transition element. Fe :1s 2s 2p ................................................................................................ ........................................................................................................................ ........................................................................................................................[2]3+ 2 2 6

(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]

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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 Fe given below. + 2+ 2+

2+

is

MnO4 (aq) + 8H (aq) + 5Fe (aq) Mn (aq) + 4H2O(l) + 5Fe (aq) Explain, in terms of electron transfer, why this reaction involves both oxidation and reduction. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[2]

3+

(iii)

A student analyses a 0.675 g sample of moss killer using the method described. In stage 4, the student uses 22.5 cm of 0.0200 mol dm endpoint.3 3

MnO4 to reach the

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

2+

Cu(OH) 2(s) + 6H2O(l) [Cu(NH3)4(H2O)2] (aq) +2+

(a)

Describe the observations that would be made as ammonia is added drop by drop until it is in an excess. ........................................................................................................................ ........................................................................................................................[2]

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(b)

Draw the shape for the [Cu(H2O)6] diagram.

2+

ion. Include the bond angles in your

[2] [Total 4 marks]

39.

Water is a simple molecule. The HOH bond angle in an isolated water molecule is 104.5. The diagram shows part of the [Cu(H2O)6] water ligand.2+

ion and the HOH bond angle in the H

C

2u +

O

1 H

0

7

Explain why the HOH bond angle in the water ligand is 107 rather than 104.5. ................................................................................................................................. ................................................................................................................................. ................................................................................................................................. .................................................................................................................................[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]

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(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.

........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[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 I2 + 2e

+

2Cr

3+

+ 7H2O 2I

E = +1.33 V

E = +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]

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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 3 3 solution up to 250 cm . The student then carried out a titration in which 25.00 cm of 3 3 this solution of B were neutralised by exactly 23.20 cm of 0.200 mol dm 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] Quality of Written Communication [1] [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 3 and made up to 250 cm using distilled water. An excess of aqueous potassium iodide was added to a 25.0 cm portion of the solution from the volumetric flask and the liberated iodine was titrated with 3 3 0.100 mol dm sodium thiosulphate. 20.0 cm of aqueous sodium thiosulphate were required to remove the iodine.3

(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]

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(c)

The reactions taking place in this titration may be summarised as follows. 2Cu2+

+ 4I

2CuI + I2 2I + S4O6 2

I2 + 2S2O3

2

(i)

Calculate the amount, in moles, of sodium thiosulphate in 20.0 cm of solution.

3

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

(ii)

For every one mole of Cu ions present in solution, deduce the amount, in 2 moles, of S2O3 ions needed for the titration.

2+

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

(iii)

What is the amount, in moles, of Cu solution?

2+

ions present in 25.00 cm of

3

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

(iv)

Calculate the percentage by mass of copper in the sample of brass.

answer ...................... % Cu[3] [Total 11 marks]

46.

The Co (a)

2+

ion can form complexes with two different co-ordination numbers.

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

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(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 2+ added to [Co(H2O)6] ? from ............................................... to ..................................................[2]

(iii)

Describe how you would move the position of this equilibrium to the left. ...............................................................................................................[1] [Total 6 marks]

47.

In this question, one mark is available for the quality of use and organisation of scientific terms. 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] Quality of Written Communication [1] [Total 9 marks]

49.

The table below shows the enthalpy changes needed to calculate the lattice enthalpy of calcium oxide, CaO. process first ionisation energy of calcium second ionisation energy of calcium first electron affinity of oxygen second electron affinity of oxygen enthalpy change of formation of calcium oxide enthalpy change of atomisation of calcium enthalpy change/ kJ mol +590 +1150 141 + 791 635 +178431

Strode's College

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]

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(ii)

Suggest why the second electron affinity of oxygen is positive. ............................................................................................................... ............................................................................................................... ...............................................................................................................[2]

(b)

Complete the BornHaber cycle for calcium oxide below. Use the data in the table to calculate the lattice enthalpy of calcium oxide.

e n k J

e

m

1

r g y / o l C C C a a a ( s ) ( g ) +2+

O 0 0

( g . 5 . 5

) O O ( g ( g ) )

( s )

2+

C

a

O

( s )

lattice enthalpy = ............................ kJ mol

1

[5]

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(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) Hf /kJ mol S /J K 1 1

C(s) 0 5.7

Ca(s) 0 41.4

CO(g) 110 197.6

635 39.7

mol

1

(i)

Calculate the standard enthalpy change for the CaO reduction in the equation.

H = ............................................ kJ mol

1

[1]

(ii)

Calculate the standard entropy change for the CaO reduction in the equation.

S = ......................................... 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]

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51.

Use the standard electrode potentials in the table below to answer the questions that follow. I II III IV Fe (aq) + 2e V (aq) + e+ 3+ 2+

Fe(s) V (aq) H2(g) 2+

E = 0.44 V E = 0.26 V E = 0.00 V 2H2O(l) E = +0.40 V

2H (aq) + 2e+

O2(g) + 4H (aq) + 4e

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 II III IV Fe (aq) + 2e V (aq) + e+ 3+ 2+

Fe(s) V (aq) H2(g) 2+

E = 0.44 V E = 0.26 V E = 0.00 V 2H2O(l) E = +0.40 V

2H (aq) + 2e+

O2(g) + 4H (aq) + 4e

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]

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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 BornHaber cycle and the following enthalpy changes. name of process enthalpy change of formation of MgCl2(s) enthalpy change of atomisation of magnesium first ionisation energy of magnesium second ionisation energy of magnesium enthalpy change of atomisation of chlorine electron affinity of chlorine enthalpy change / kJ mol 641 +148 +738 +1451 +123 3491

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] Quality of Written Communication [1] [Total 12 marks]

54.

The standard electrode potential of Cu (aq) + 2e (a)

2+

Cu(s) is +0.34 V.

Define the term standard electrode potential. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[3]

(b)

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

c o

p

p

e

r

r o

d

C

2 u (+

a

q

)

[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]

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(ii)

Complete the electronic configuration of a chromium atom. 1s 2s 2p ..............................................................................................[1]2 2 6

(b)

The following equations relate to half-cells involving iron and chromium ions. Fe3+

+e2

Fe+

2+

E = +0.77 V 2Cr3+

Cr2O7 V

+ 14H + 6e

+ 7H2O

E = +1.33

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. H O S H O O O

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 (i)

+

+ SO4

2

+

I

I2

+

H2S

+

H2O

Write the oxidation numbers of sulphur and iodine in the boxes above the equation.[2]

(ii)

Balance the equation above.

[1] [Total 3 marks]

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57.

The table below shows the enthalpy changes needed to calculate the enthalpy change of formation of calcium oxide. process lattice enthalpy for calcium oxide first ionisation energy for calcium second ionisation energy for calcium first electron affinity for oxygen second electron affinity for oxygen enthalpy change of atomisation for oxygen enthalpy change of atomisation for calcium enthalpy change/kJ mol 3459 +590 +1150 141 +798 +249 +1781

(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) Include

Draw a Born-Haber cycle for calcium oxide.

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 . Suggest a reason for the difference in lattice enthalpy between calcium oxide and iron(II) oxide. ............................................................................................................... ...............................................................................................................[1] [Total 8 marks]

1

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58.

The standard electrode potentials for some redox systems involving vanadium are shown below. These are labelled A, B, C and D. E /V A B C D VO2 + 2H + e V V3+ + +

VO V2+

2+

+ H2O

+1.00

+e

0.26

2+

+ 2e

V 1.20+

VO

2+

+ 2H + e

V

3+

+ 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. V

[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]

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59.

Concentrated nitric acid is a powerful oxidising agent. Concentrated nitric acid oxidises sulphur 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.

1 The standard electrode potential of the 2 Cl2/ Cl half-cell may be measured using the following apparatus.C s a H2

lt

b

r i d

g

e D

( g

)

B A

C

l

( a

q

)

(a)

Suggest suitable labels for A, B, C and D. A .................................................................................................................... B .................................................................................................................... C .................................................................................................................... D ....................................................................................................................[2]

(b)

The half cell reactions involved are shown below.

1 2 Cl2 + e

Cl

E = +1.36 V

H +e (i)

+

1 2 H2

E = 0.00V

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 E are measured under standard conditions. What are the standard conditions? ............................................................................................................... ............................................................................................................... ...............................................................................................................[2]

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(c)

The half cell reaction for

ClO3 /

1 2 Cl2 is shown below. 1 2 Cl2 + 3H2OE = +1.47 V

ClO3

+ 6H + 5e

+

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 first ionisation energy of sodium first electron affinity of oxygen second electron affinity of oxygen enthalpy change of formation for sodium oxide enthalpy change of atomisation for sodium enthalpy change of atomisation for oxygen enthalpy change / kJ mol +495 141 +791 416 +109 +2471

(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. 2 N+ a ( g ) +2

O

( g

)

2

N+ a

( g H

)

+ = N+ a

O (H g

) = + . . 2 . . e . . . . . . k J

. . . . . . . . . . k J ( g)

H

=

. . . . . . . . . . k J 2 2 N + ( ag ) 12 O+ 2

) + 2

+ e

O

( g

)

+

e

( g

H

=

. . . . . . . . . . k J 2 N a ( 12 gO 2 ) +( g )

la t t ic e e n t h a lp y o f s o d i u m o x i d

e

H

=

. . . . . . . . . . k J 2 N a ( 12 sO 2) ( g + )

H

=

. . . . . . . . . . k J N2a

O

( s )[4]

(b)

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

lattice enthalpy = ....................................kJ mol

1

[2]

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(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. E /V + 0.80

Ag + e 1 2 Cl2 + e Cu + 2e 3+ Fe + e 1 2 I2 + e2+

+

Ag Cl

+ 1.36 + 0.34 + 0.77 + 0.54

Cu 2+ Fe

I

(a)

Define the term standard electrode potential. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[3]

(b)

The diagram below shows an incomplete cell consisting of Cu/Cu half-cells.

2+

and Ag/Ag

+

C

u

( s )

A

+g

( a

q

)

(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]

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(iii)

Calculate the standard cell potential.

standard cell potential = V[1]

(iv)

Write the overall cell reaction. ...............................................................................................................[1]

(c)

Chlorine will oxidise Fe to Fe electrode potential data.

2+

3+

but iodine will not. Explain why, using the

........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[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 first ionisation energy of calcium second ionisation energy of calcium electron affinity of chlorine enthalpy change of formation for calcium chloride enthalpy change of atomisation for calcium enthalpy change of atomisation for chlorine enthalpy change / kJ mol +590 +1150 348 7961

+178 +122

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(a)

The Born-Haber cycle below can be used to calculate the lattice enthalpy for calcium chloride. C2a +

( g

)

+

2

C

l( g

)

+

2

e

H

=

. . . . . . . . . . . . . 1. . . . . . . C2

k J )2+

m C m2+

o l o Cl

l ( g l ( g l )C ) + ) +

a +( g

H = 2 e2a +

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

k

H

=

. . . . . . . . . . . . . 1. . . . . . . C + a( g

k J ) k J

C e

( g

)

+

2

C

l

( g

)

H

=

. . . . . . . . . . . . . 1. . . . . . . C a

m

o

( g l 2 ) ( +g k J a m + o2

H

=

. . . . . . . . . . . . . 1. . . . . . . C

o

l C l l ( s ) l ( g )

l a t t ic e e c a l c i u m

n

t h a l p y o c h l o r i d e

( s 2) m C a

H

=

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

k J

C

(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]

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(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 , for the thermal decomposition of barium nitrate using the enthalpy changes of formation, Hf, given in the table. compound Ba(NO3)2(s) BaO(s) NO2(g) Hf /kJ mol 992 558 +33 answer ........................... kJ mol1 1

1

[3]

(b)

A student investigates the volume of gas formed when barium nitrate is heated. The diagram shows the apparatus the student uses.

1

0

03 c m

g

a

s

s y r in

g

e

b

a

r i u

m

n

i t r a

t e

h

e

a

t

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(i)

A 1.31 g sample of barium nitrate is completely decomposed. Use the equation above to calculate the volume, in cm , of gas formed at room temperature and pressure. 1 mol of gas molecules occupies 24 000 cm at room temperature and pressure.3 3

answer ......................... cm

3

[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.

1 2 Cl2 + eMnO4 + 8H + 5e +

Cl Mn2+

E = +1.36 V E = +1.52 V

+ 4H2O

(a)

Define the term standard electrode potential. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[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.

1 2 Cl2 + eMnO4 + 8H + 5e +

Cl Mn2+

E = +1.36 V E = +1.52 V

+ 4H2O

(a)

Use the half-equations above to: (i) construct an ionic equation for the reaction between hydrochloric acid and potassium manganate(VII); ................................................................................................................. ................................................................................................................. .................................................................................................................[2]

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(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 BrnstedLowry acid. C6H5OH(aq) H (aq) + C6H5O (aq)+

Ka = 1.3 10

10

mol dm

3

Define the following terms: (i) A BrnstedLowry acid, ........................................................................................................................[1]

(ii)

A weak acid. ........................................................................................................................[1] [Total 2 marks]

69.

When phenol is mixed with aqueous sodium hydroxide, an acidbase reaction takes place. C6H5OH(aq) ...................... In the available spaces, label one conjugate acidbase pair as acid 1 and base 1, label the other conjugate acidbase pair as acid 2 and base 2.[Total 1 mark]

+

OH (aq) .....................

C6H5O (aq) + .......................

H2O(l) .....................

70.

A solution of phenol in water has a concentration of 4.7 g dm . (i) Write an expression for the acid dissociation constant, Ka, of phenol.

3

[1]

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(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 volume of sodium phenoxide.3

solution of phenol, mixed with an equal

Use your knowledge of buffer solutions to determine the concentration of sodium 3 phenoxide solution that the student would need to mix with the 0.200 mol dm 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 dm sealed vessel. The equilibrium is shown below. CO(g) + 2H2(g) CH3OH(g)3

The number of moles of each component at equilibrium is shown below component number of moles at equilibrium CO(g) 6.20 103

H2(g) 4.80 102

CH3OH(g) 5.20 105

(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]

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(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. Explain your reasoning. ............................................................................................................... ...............................................................................................................[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 1 2 3 [NO] 3 / mol dm 0.10 0.10 0.30 [H2] / mol dm 0.20 0.50 0.503

initial rate 3 1 / mol dm s 2.6 6.5 58.5

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

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(i)

For each reactant, deduce the order of reaction. Show your reasoning. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................[4] Quality of Written Communication [1]

(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. ...............................................................................................