Cambridge International AS & A Level

CHEMISTRY 9701/42
Paper 4 A Level Structured Questions October/November 2024
MARK SCHEME
Maximum Mark: 100

Published

This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the
examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the
details of the discussions that took place at an Examiners’ meeting before marking began, which would have
considered the acceptability of alternative answers.

Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for
Teachers.

Cambridge International will not enter into discussions about these mark schemes.

Cambridge International is publishing the mark schemes for the October/November 2024 series for most
Cambridge IGCSE, Cambridge International A and AS Level components, and some Cambridge O Level
components.

This document consists of 12 printed pages.

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Generic Marking Principles

These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the
specific content of the mark scheme or generic level descriptions for a question. Each question paper and mark scheme will also comply with these
marking principles.

GENERIC MARKING PRINCIPLE 1:

Marks must be awarded in line with:

• the specific content of the mark scheme or the generic level descriptors for the question
• the specific skills defined in the mark scheme or in the generic level descriptors for the question
• the standard of response required by a candidate as exemplified by the standardisation scripts.

GENERIC MARKING PRINCIPLE 2:

Marks awarded are always whole marks (not half marks, or other fractions).

GENERIC MARKING PRINCIPLE 3:

Marks must be awarded positively:

• marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond
the scope of the syllabus and mark scheme, referring to your Team Leader as appropriate
• marks are awarded when candidates clearly demonstrate what they know and can do
• marks are not deducted for errors
• marks are not deducted for omissions
• answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the
question as indicated by the mark scheme. The meaning, however, should be unambiguous.

GENERIC MARKING PRINCIPLE 4:

Rules must be applied consistently, e.g. in situations where candidates have not followed instructions or in the application of generic level
descriptors.

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GENERIC MARKING PRINCIPLE 5:

Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may
be limited according to the quality of the candidate responses seen).

GENERIC MARKING PRINCIPLE 6:

Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or
grade descriptors in mind.

Science-Specific Marking Principles

1 Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks
should not be awarded if the keywords are used incorrectly.

2 The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for
any correct statement that is contradicted within the same question part. Wrong science that is irrelevant to the question should be ignored.

3 Although spellings do not have to be correct, spellings of syllabus terms must allow for clear and unambiguous separation from other
syllabus terms with which they may be confused (e.g. ethane / ethene, glucagon / glycogen, refraction / reflection).

4 The error carried forward (ecf) principle should be applied, where appropriate. If an incorrect answer is subsequently used in a scientifically
correct way, the candidate should be awarded these subsequent marking points. Further guidance will be included in the mark scheme
where necessary and any exceptions to this general principle will be noted.

5 ‘List rule’ guidance

For questions that require n responses (e.g. State two reasons …):

• The response should be read as continuous prose, even when numbered answer spaces are provided.
• Any response marked ignore in the mark scheme should not count towards n.
• Incorrect responses should not be awarded credit but will still count towards n.
• Read the entire response to check for any responses that contradict those that would otherwise be credited. Credit should not be
awarded for any responses that are contradicted within the rest of the response. Where two responses contradict one another, this
should be treated as a single incorrect response.
• Non-contradictory responses after the first n responses may be ignored even if they include incorrect science.

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6 Calculation specific guidance

Correct answers to calculations should be given full credit even if there is no working or incorrect working, unless the question states ‘show
your working’.

For questions in which the number of significant figures required is not stated, credit should be awarded for correct answers when rounded
by the examiner to the number of significant figures given in the mark scheme. This may not apply to measured values.

For answers given in standard form (e.g. a  10n) in which the convention of restricting the value of the coefficient (a) to a value between 1
and 10 is not followed, credit may still be awarded if the answer can be converted to the answer given in the mark scheme.

Unless a separate mark is given for a unit, a missing or incorrect unit will normally mean that the final calculation mark is not awarded.
Exceptions to this general principle will be noted in the mark scheme.

7 Guidance for chemical equations

Multiples / fractions of coefficients used in chemical equations are acceptable unless stated otherwise in the mark scheme.

State symbols given in an equation should be ignored unless asked for in the question or stated otherwise in the mark scheme.

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Question Answer Marks

1(a)(i) Change in concentration = 0.135 [1] 2

0.135 / 1800 = 7.5  10–5 [1]

1(a)(ii) Rate = k[X] [1] 1

1(a)(iii) k = 0.693 / t½ / k = 0.693 / 900 / k = ln2 / t½ / k = ln2 / 900 / t½ = ln2 / k [1] 1

1(a)(iv) 1.16  10–4 [1] 2

mol dm–3 s–1 [1]

1(b)(i) Any two from: 1

• variable oxidation state
• vacant / empty / unfilled d orbitals [1]
• can form dative bonds / can accept electrons

1(b)(ii) Iron AND 1

iron is solid, reactants are gases OR
catalyst and reactants are in different phases / states [1]

1(b)(iii) Two for one mark, three for two marks: 2

• adsorption of reactants by Pt
• bonds of reactants weaken [1]
• desorption of products [1]

1(b)(iv) NO2 + SO2 → NO + SO3 AND 1

2NO + O2 → 2NO2 [1]

1(c) BiO+ [1] 3

3H2SO3 + 2BiO+ + H2O → 3SO42- + 8H+ + 2Bi [1]
0.11 V [1]

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Question Answer Marks

2(a) Hhyd increases from left to right due to increase in charge [1] 3
ionic radius decreases from left to right [1]
causing increased attractive force to water molecules [1]

2(b)(i) Mg2+ (aq) + 2Cl– (aq) [1] 1

2(b)(ii) Enthalpy change of hydration of magnesium ions and chloride ions [1] 2
HhydMg2+ + 2HhydCl– [1]

2(b)(iii) Selects 155, 1920 and 364 only [1] 3

2  364 [1]
answer –2493 [1]

2(c) The number of arrangements of the particles and of the energy in the system [1] 1

2(d) G = H – TS [1] 2

answer +10.5 [1]

2(e)(i) No, G is positive [1] 1

2(e)(ii) Becomes more / soluble because G becomes more negative / less positive / smaller / closer to zero [1] 1

Question Answer Marks

3(a)(i) [H+] = 10–12.35 OR [H+] = 4.47  10–13 [1] 2

Kw / 4.47  10–13 [1]
OR
pOH = 1.65 [1]
[OH–] = 10–1.65 [1]

3(a)(ii) Ksp = (0.0112)(0.0224)2 OR Ksp = [Ca2+][OH–]2 [1] 3

answer 5.62  10–6 [1]
mol3 dm–9 [1]

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Question Answer Marks

3(a)(iii) white solid / white ppt AND pH between 7.01 and 12.34 [1] 3
common ion effect [1]
hydroxide removed by precipitation OR ppt is Ca(OH)2 [1]

3(a)(iv) lattice energy and hydration energy greater for CaSO4 OR 3

lattice energy and hydration energy decrease down group [1]
hydration energy decreases more / is dominant factor [1]
enthalpy of solution is more endothermic for BaSO4 OR is more endothermic down grp [1]

3(b)(i) Ca + 2CH3COOH → Ca(CH3COO)2 + H2 [1] 1

3(b)(ii) Pair 1: CH3COOH and CH3COO– [1] 2

Pair 2: H3O+ and H2O OR H2O and OH– [1]

3(b)(iii) [H+ ][CH3COO− ] 1

[1]
[CH3COOH]

3(b)(iv) [CH3COO–] = 0.788, [CH3COOH] = 0.270 2

[H+] = 5.96  10–6 [1]
pH = 5.22 [1]

3(b)(v) CH3COO– + H+ → CH3COOH 2

OR Ca(CH3COO)2 + 2H+ → 2CH3COOH + Ca2+ [1]
CH3COOH + OH– → CH3COO– + H2O [1]

Question Answer Marks

4(a)(i) red/pink blue [1] 1

4(a)(ii) [Co(H2O)6]2+ + 2OH– → Co(H2O)4(OH)2 + 2H2O [1] 1

4(a)(iii) acid-base [1] 1

4(b)(i) [CoL2]2+ [1] 1

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Question Answer Marks

4(b)(ii) +2 [1] 1

4(b)(iii) 2 1
3 [1]

4(b)(iv) Not of the same energy / have different energy [1] 1

4(c)(i) 5Fe2+ + MnO4– + 8H+ → 5Fe3+ + Mn2+ + 4H2O [1] 1

4(c)(ii) 0.02  18.7/1000 = 3.74  10–4 [1] 2

3.74  10–4  5 = 1.87  10–3 [1]

4(c)(iii) 1.87  10–3  10 = 1.87  10–2 2

4.18/1.87  10–2 = 224 / 223.5(294) [1]
n=2 [1]

Question Answer Marks

5(a) [[Ni(en )3 ]2+ ] [[Ni(en )3 ]2+ ] 1

Kstab = OR [1]
[Ni2+ ][en]3 [Ni(H2O)62+ ][en]3

5(b)(i) [Ni(en)3]2+ AND 1

larger Kstab OR more stable [1]

5(b)(ii) [Ni(H2O)6]2+ + 3en → [Nien3]2+ + 6H2O [1] 1

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Question Answer Marks

5(c) 3

octahedral with correct 3D for one [Ni(en)3]2+ [1]

second optical isomer [1]
optical isomerism [1]

Question Answer Marks

6(a)(i) ClOCCOCl [1] 1

6(a)(ii) PCl3 / PCl5 [1] 1

6(b) oxygen [1] 2

acidified KMnO4 [1]

6(c) C=O are electron withdrawing / electronegative [1] 2

weakens O–H bond OR stabilises anion [1]

6(d)(i) 1

[1]

6(d)(ii) step 1: CH3Cl + AlCl3 [1] 2

step 2: hot alkaline KMnO4 [1]

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Question Answer Marks

6(d)(iii) 2

correctly displayed ester linkage [1]

rest of structure [1]

6(d)(iv) condensation AND ester [1] 1

Question Answer Marks

7(a) aluminium chloride OR AlCl3 [1] 1

7(b)(i) delocalised system / delocalised ring / pi system / pi ring [1] 2

C–Cl bond [1]

7(b)(ii) C–H bond [1] 2

delocalised system / delocalised ring / pi system / pi ring [1]

7(c) 0, 5, 1 [1] 1

7(d) C6H6 + Cl2 → C6H5Cl + HCl [1] 1

7(e) Cl + 1
hydrogen / H
chlorine / Cl [1]

7(f)(i) nucleophilic substitution AND ethanol [1] 1

7(f)(ii) delocalisation of LP of Cl with  system [1] 2

C–Cl bond is stronger in chlorobenzene / partly double [1]

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Question Answer Marks

8(a) biological activity [1] 1

8(b) rotates plane polarised light 5.0° in anticlockwise direction [1] 1

8(c) enantiomers [1] 1

8(d) racemic [1] 1

8(e) use of chiral catalyst [1] 1

8(f) CH2 and CH only in column one [1] 3

CH2 gives a doublet, CH gives a triplet [1]
doublet due to 1 proton on neighbouring carbons
triplet due to 2 protons on neighbouring carbons [1]

8(g) 5 [1] 1

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Question Answer Marks

8(h) 3

at pH 1 [1]

at pH 3 AND

or
at pH 9 [1]

at pH 14 [1]

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