Cambridge International AS & A Level

CHEMISTRY 9701/21
Paper 2 AS Level Structured Questions May/June 2025
MARK SCHEME
Maximum Mark: 60

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 May/June 2025 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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Annotations guidance for centres

Examiners use a system of annotations as a shorthand for communicating their marking decisions to one another. Examiners are trained during the
standardisation process on how and when to use annotations. The purpose of annotations is to inform the standardisation and monitoring
processes and guide the supervising examiners when they are checking the work of examiners within their team. The meaning of annotations and
how they are used is specific to each component and is understood by all examiners who mark the component.

We publish annotations in our mark schemes to help centres understand the annotations they may see on copies of scripts. Note that there may
not be a direct correlation between the number of annotations on a script and the mark awarded. Similarly, the use of an annotation may not be an
indication of the quality of the response.

The annotations listed below were available to examiners marking this component in this series.

Annotations

Annotation Meaning

Correct point or mark awarded

Incorrect point or mark not awarded

Unclear

Information missing or insufficient for credit

Benefit of the doubt given

Contradiction in response otherwise markworthy, mark not given

Part of the correct answer has been seen. Full credit has not been awarded.

Error carried forward applied

Incorrect or insufficient point ignored while marking the rest of the response

Benefit of the doubt not applied in this instance

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Annotation Meaning

Rounding error

Repetition

Blank page or part of script seen

Error in number of significant figures

Transcription error

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Question Answer Marks

1(a)(i) sodium – metallic 1

AND sodium oxide – ionic

1(a)(ii) delocalised electrons move (through the structure) 1

1(a)(iii) (sodium and oxide) ions move (through the liquid) 1

1(b)(i) 2Na + 2H2O → 2NaOH + H2 1

1(b)(ii) Na2O + H2O → 2NaOH 1

1(b)(iii) 2
sodium sodium oxide

(both) solids disappear

one similarity
OR (both produce) colourless solutions

one difference effervescence no effervescence

1(c) M1 NaCl +1 AND PCl 5 + 5 2

M2 Na has only 1 valence (shell) electrons AND P has 5

1(d) All three for two marks: 2

• false
• comparison or statement of oxidation number
• correct link to melting point from their comparison or statement

Question Answer Marks

2(a) atoms (of an element) with same number of protons and different number of neutrons 1

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Question Answer Marks

2(b)(i) M1 method showing each abundance multiplied by m/e value 2

• (5.9  54) and (91.9  56) and (2.2  57)
OR
• (0.59  54) and (9.19  56) and (0.22  57)

M2 the three values from M1 expressed as a percentage and added together correctly with final answer to 1 d.p
5.9 91.9 2.2
 54 +  56 +  57 = 55.9
100 100 100

2(b)(ii) 2
particle number of particles in one atom of 56Fe

protons 26

nucleons 56

2(c) 5 1

2(d) Fe(g) → Fe+(g) + e(-) 1

2(e) M1 same electronic configuration OR same shielding 4

M2 same number of protons OR same nuclear charge
M3 so same nuclear attraction to outer shell electron
M4 no change / will not be affected

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Question Answer Marks

3(a)(i) 2

Two correct for one mark, all four for two marks:
• start at origin
• peak sits below the original
• peak sits to the right-hand side of the original
• new line crosses the original once only AND to the right of the original peak

3(a)(ii) M1 greater proportion of (H2) molecules have energy greater than or equal to the activation energy /  EA 2
M2 increase in frequency of successful collisions (between H2 and C6H12)

3(a)(iii) catalyst 1

3(a)(iv) annotation to show new EA (nickel / catalyst) further to the left than original EA 1

3(b) M1 (if a change is made at a system is dynamic equilibrium) the equilibrium moves 2
M2 to minimise the change in conditions

3(c) (forward) reaction is exothermic 2

(a + b)  c

Question Answer Marks

4(a) C3H4O3 1

4(b)(i) (28.40 / 1000  0.0005) = 1.42  10-5 mol 1

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Question Answer Marks

4(b)(ii) (1.42  10 -5  176  200 / 5) = 0.099968 2

M1 correct method to deduce mass of vit C in 5 cm3 sample

(1.42  10–5  176) = 2.49  10–3
M2 correct calculation for mass of vit C in original solution
(2.49  10–3  200 / 5) = 0.099968

OR

M1 correct method to deduce amount, mol, vit C in 5 cm3 sample

(1.42  10–5  200 / 5) = 5.68  10–4
M2 correct calculation for mass of vit C in original solution = M1  176
(5.68 10–4)  176 = 0.099968

4(b)(iii) oxidising agent 1

4(b)(iv) M1 (also) oxidises / reacts with (primary and / or secondary) alcohol groups 2
M2 (also) breaks the sigma and pi bond in C=C

4(c) Any two complete rows from: 2

wavenumber bond functional group

1040 – 1300 C–O ester / hydroxy

3200 – 3650 O–H hydroxy / alcohols

2850 – 2950 C–H alkane

1710 – 1750 C=O ester

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Question Answer Marks

5(a) M1 two ester links 2

M2 rest of structure correct

5(b) (acid) hydrolysis 1

5(c)(i) HOOCCH2COOH + Na2CO3 → NaOOCCH2COONa +CO2 + H2O 1

5(c)(ii) C is not as strong an acid as B 1

5(d)(i) M1 NaOH(aq) AND heat 2

M2 acidified AND potassium dichromate(VI) AND heat under reflux

5(d)(ii) oxidation 1

5(e)(i) LiAl H4 1

5(e)(ii) M1 correct unambiguous organic product 2

M2 correct balanced equation

HOOCCH2COOH + 8[H] → HOCH2CH2CH2OH + 2H2O

5(e)(iii) 1,3-dichloropropane 1

Question Answer Marks

6(a) carbonyl 1

6(b) M1 (2,4)-dinitrophenylhydrazine / (2,4)-DNPH 2

M2 orange / red / yellow precipitate

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Question Answer Marks

6(c)(i) F = propanone 2
G = ethanal
H = propanal

6(c)(ii) tri-iodomethane OR CHI3 1

6(c)(iii) CH3CH(OH)-R where R is represented as H or any alkyl group 1

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