CHEMISTRY 9701/42 Paper 4 A Level Structured Questions 2022
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CHEMISTRY 9701/42
Paper 4 A Level Structured Questions
2022
1 Iodine is found naturally in compounds in many different oxidation states.
(a) Iodide ions, I– , react with acidified H2O2(aq) to form iodine, I2 , and water.
(i) Identify the role of H2O2(aq) in its reaction with I– ions in acidic conditions. Write an ionic equation for the reaction.
role ......................................................................................................................................
ionic equation .....................................................................................................................
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[2]
(ii) 15.0cm3 of C6H12 is shaken with 20.0cm3 of an aqueous solution containing I2 until no
Calculate the mass of I2 that remains in the aqueous layer.
Show your working.
mass of I2 in aqueous layer = .............................. g [2]
(iii) Suggest how the value of Kpc of I2 between hexan-2-one, CH3(CH2)3COCH3 , and water
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(b) The Group 1 iodides all form stable ionic lattices and are soluble in water.
(i) Define enthalpy change of solution.
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(ii) Use the data in Table 1.1 to calculate the enthalpy change of solution of potassium iodide,
KI.
Table 1.1
process |
enthalpy change, ∆H/kJmol–1 |
K+(g) + I– (g) → KI(s) |
–629 |
K+(g) → K+(aq) |
–322 |
I– (g) → I– (aq) |
–293 |
enthalpy change of solution = .............................. kJ mol–1 [1]
(iii) Suggest the trend in the magnitude of the lattice energies of the Group 1 iodides, LiI, NaI,
KI.
Explain your answer.
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....................................................................................................................................... [2]
(c) The concentration of Cu2+(aq) in a solution can be determined by the reaction of Cu2+ ions with I– ions.
reaction 1 2Cu2+ + 4I– → 2CuI + I2
The I2 produced in reaction 1 is titrated against a solution containing thiosulfate ions, S2O32– , using a suitable indicator.
reaction 2 2S2O32– + I2 → S4O62– + 2I–
(i) A 25.0cm3 portion of a Cu2+(aq) solution reacts with an excess of I– (aq).
concentration of Cu2+(aq) = .............................. mol dm–3 [2]
(ii) Identify a suitable indicator for the titration.
....................................................................................................................................... [1]
(iii) Copper(I) and copper(II) both contain electrons in all five 3d orbitals.
Sketch the shape of a 3dxy orbital on the axes provided.
z
y
x
[1]
(d) The reaction of I– ions with persulfate ions, S2O82– , can be catalysed by Fe3+ ions.
2I– + S2O82– → I2 + 2SO42–
Write equations to show how Fe3+ catalyses this reaction.
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.............................................................................................................................................. [2]
(e) An orange precipitate of HgI2 forms when Hg2+ ions are added to KI(aq).
Calculate the solubility product, Ksp , of HgI2 .
Include units in your answer.
[Mr: HgI2 , 454.4]
value of Ksp = ..............................
units = ..............................
[3] [Total: 19]
2 Silicon is the second most abundant element by mass in the Earth’s crust.
(a) In industry, silicon is extracted from SiO2 by reaction with carbon at over 2000 °C.
reaction 1 SiO2(s) + 2C(s) → Si(l) + 2CO(g)
(i) Explain why the entropy change, ∆S, of reaction 1 is positive.
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(ii) Reaction 1 is highly endothermic.
Suggest the effect of an increase in temperature on the feasibility of this reaction. Explain your answer.
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(b) Silicon is purified by first heating it in a stream of HCl(g) to form SiHCl3 . The SiHCl3 formed is
reaction 2 Si(s) + 3HCl(g) → SiHCl3(g) + H2(g)
(i) Table 2.1 shows some standard entropy data.
Table 2.1
compound |
standard entropy, S |
Si(s) |
19 |
HCl(g) |
187 |
SiHCl3(g) |
314 |
H2(g) |
131 |
Use the data in Table 2.1 to calculate ∆So for reaction 2.
∆S o = .............................. J K–1 mol–1 [2]
(ii) Reaction 3 is the reverse of reaction 2 and is used to obtain pure silicon.
reaction 3 SiHCl3(g) + H2(g) → Si(s) + 3HCl(g) ∆H = +219.3 kJmol–1
Use this information and your answer to (b)(i) to calculate the temperature, in K, at which reaction 3 becomes feasible.
Show your working.
[If you were unable to answer (b)(i), you should use ∆So = –150 J K–1 mol–1 for reaction 2. This is not the correct answer to (b)(i).]
temperature = .............................. K [2]
(c) Silicon can also be produced by electrolysis of SiO2 dissolved in molten CaCl2 . The relevant half-equation for the cathode is shown.
SiO2 + 4e– → Si + 2O2–
Calculate the time, in seconds, required to produce 1.00g of Si by this electrolysis, using a current of 6.00A.
Assume no other substances are produced at the cathode.
time = .............................. s [2]
[Total: 9]
3 Titanium is a transition element in Period 4. It is commonly found as TiO2 in minerals. (a) (i) Define transition element.
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(ii) Identify two typical properties of transition elements.
1 ..........................................................................................................................................
2 ..........................................................................................................................................
[1]
(b) The TiO2+ ion forms when TiO2 reacts with an excess of sulfuric acid.
TiO2+ can be reduced by zinc metal in acidic conditions to form a purple solution containing Ti3+(aq).
(i) TiO2+(aq) is a colourless ion. Suggest why.
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(ii) Give the electronic configuration of an isolated Ti3+ ion.
1s2 ................................................................................................................................. [1]
(iii) Write an ionic equation for the reduction of TiO2+ by zinc metal in acidic conditions.
....................................................................................................................................... [1]
(c) Acidified Ti3+(aq) reacts with oxygen dissolved in water as shown.
4Ti3+ + O2 + 2H2O → 4TiO2+ + 4H+ ∆Go = –436.1kJmol–1
The standard reduction potential, Eo , of O2 + 4H+ + 4e– 2H2O is +1.23 V.
(i) Calculate the standard reduction potential, Eo , in V, of the TiO2+(aq) /Ti3+(aq) half-cell. Show your working.
Eo = .............................. V [3]
(ii) When aqueous citrate ions, C6H5O73– , are added to Ti3+(aq), the [Ti(C6H5O7)2]3–(aq) complex
Explain, in terms of d-orbitals, why Ti3+ is able to form complex ions.
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(iii) Acidified [Ti(C6H5O7)2]3–(aq) does not react with oxygen dissolved in water, unlike acidified
Suggest what this means for the value of the standard reduction potential, Eo , of the following half-cell.
[Ti(C6H5O7)2]2–(aq) + e– [Ti(C6H5O7)2]3–(aq)
Explain your answer.
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(d) Some reactions of TiO2 are shown in Fig. 3.1. The anion, acac– , is a bidentate ligand.
TiO2 2 TiCl4 Ti(acac)2Cl2
HF
TiF 2–
Fig. 3.1
(i) The titanium ions in TiF62– and Ti(acac)2Cl2 have a coordination number of 6. State what is meant by coordination number.
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(ii) Write an equation for the formation of TiF62– from TiO2 .
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(iii) State what is meant by bidentate ligand.
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(iv) Ti(acac)2Cl2 shows both optical and geometrical (cis/trans) isomerism.
Ti(acac)2Cl2 exists as three stereoisomers.
The structure of one stereoisomer of Ti(acac)2Cl2 is shown in Fig. 3.2. stereoisomer 1
Fig. 3.2
Complete the structures of the other two stereoisomers of Ti(acac)2Cl2 .
stereoisomer 2
Ti
|
[2]
(v) The acac– anion is symmetrical.
Deduce which, if any, of stereoisomers 1, 2 and 3 in (d)(iv) are polar. Explain your answer.
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[Total: 19]
4 Compounds F and J are shown in Fig. 4.1.
F
O
OH
H2N
Fig. 4.1
J
OH
O
O
(a) F and J both contain the arene functional group.
(i) Identify the other functional groups in F and J.
F: ........................................................................................................................................
J: .........................................................................................................................................
[2]
(ii) State the number of chiral centres in a molecule of F and in a molecule of J.
number of chiral centres in: F = ......................................... J = ........................................
[1]
(b) A student proposes a multi-step synthesis of F from benzene, as shown in Table 4.1.
(i) Complete Table 4.1 by providing relevant details of the reagents and conditions for steps 1
Table 4.1
step |
organic reactant |
reagent(s) and conditions |
organic product |
1 |
|
......................................... |
|
2 |
|
concentrated HNO3 and concentrated H2SO4 |
D |
3 |
D |
hot alkaline KMnO4 then dilute H2SO4 |
E COOH
O2N |
4 |
COOH
O2N |
......................................... |
F COOH
H2N |
[3]
(ii) In a second multi-step synthesis, the student changes the order in which the reagents and
Fig. 4.2
Draw the structure of G.
Explain why G is the major product of the synthesis rather than E.
2022-05-10