Cambridge International AS & A Level

CHEMISTRY 9701/33
Paper 3 Advanced Practical Skills 1 February/March 2024
MARK SCHEME
Maximum Mark: 40

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 f or
Teachers.

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

Cambridge International is publishing the mark schemes f or the February/March 2024 series f or most
Cambridge IGCSE, Cambridge International A and AS Level components, and some Cambridge O Level
components.

This document consists of 11 printed pages.

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9701/33 Cambridge International AS & A Level – Mark Scheme February/March 2024
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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 alon gside 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 assess ed 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 fu ll 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 presen t, 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 questi on should be ignored.

3 Although spellings do not have to be correct, spellings of syllabus terms must allow for clear and unambiguous separation fro m 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 i n a scientifically
correct way, the candidate should be awarded these subsequent marking points. Further guidance will be include d 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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Q marks
When awarding the accuracy (Q) mark in Question 2, each Examiner must round each temperature to the nearest .0 or .5 C, check
subtractions on the Supervisor’s and Candidate’s scripts and must use the corrected values to assess accuracy.

Penalise rounding errors or transcription errors once only on the whole paper.

Significant figure errors are penalised once per question.

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Question Answer Marks

1(a) I A single table with 4 headings for results on page 4 with indication of the 4 items of data to be recorded (volume of FA 1, 1
volume of water, time and rate)
AND
the 2 specified experiments carried out

II Correct headings and units for 4 required items of data: 1

• volume of FA 1 (used) and / cm3 or (cm3) or in cm3

• volume of (distilled) water and / cm3 or (cm3) or in cm3
• (reaction) time and /s or (s) or in seconds
• rate and /s–1 or (s–1) or in s–1

III Precision of data recorded: 1

• all volumes recorded to 2 dp with the final digit being 0 or 5 cm3
• all times to the nearest second

IV 3 additional volumes chosen with intervals not less than 2.00 cm3 1
AND
no volume less than 12.50 cm3
AND
water added in each additional experiment to make total volume of FA 1 and water equal to 25.00 cm3

V All rates correctly calculated using 1000 / time to minimum 2 sf 1

VI Reaction time decreases as volume of FA 1 increases for all five experiments 1

Examiner corrects times (if necessary) to the nearest second for Experiments 1 and 2 and calculates ratio t12.5 / t25 to 2 dp 2
Write the ratio, ringed, near the mark boxes
Award VII for ratio between 1.70–2.40
Award VII and VIII for ratio between 1.90–2.20

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Question Answer Marks

1(b) I Axes unambiguously labelled 1

(relative) rate or s–1 on y-axis
AND
volume / FA 1 / (sodium) thiosulfate / Na2S2O3 / cm3 on x-axis
AND
some numbers for scales

II Suitable scales chosen 1

Linear scales based on 1, 2 or 5
AND
scale chosen so that plotted points occupy more than half the available space along each axis

III All points recorded in the table are accurately plotted. 1

All points recorded plotted correctly to within half a small square
AND
in the correct small square or on the line if it should be on the line
AND
minimum of 4 experiment points plotted

IV Line of best fit drawn 1

1(c) M1 2 lines drawn on the graph – vertical from 23.50 on the x-axis to the line of best fit and horizontal from the line to the 2
y-axis.

M2 Correctly uses time = 1000 / (relative) rate

1(d) Time is longer 1

AND
extra water would lower the concentration / dilute (FA 1 or reactants)

1(e)(i) The student is correct (that time would be greater) 1

AND
the depth (of solution / ppt / mixture) is less

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Question Answer Marks

1(e)(ii) The student is not correct / (The (relative) rate is smaller but) the rate is not slower 1
AND
(the solution) concentrations have not changed / the frequency of successful collisions remains the same / more sulfur is
required to obscure the insert owtte.

Question Answer Marks

2(a) M1 Unambiguous headings and correct units for: 1

• (Mass of) container + FA 4 and g / grams
• (Mass of) container (+ residue) and g / grams
• Initial / FA 3 (temperature) and °C
• Maximum (temperature) and °C
• (Mass of) magnesium / FA 4 (added) and g / grams
• (Temperature) change and °C

M2 Readings are appropriately recorded against headings 1

• Both temperature measurements recorded to the nearest 0.5 °C
AND
• Both balance readings recorded to a consistent number of decimal places (either 2 or 3)
AND
• Correct calculations of mass of FA 4 and temperature change

M3 Examiner checks and corrects T if necessary 1

T within x °C of supervisor value

T sup / ºC <5.0 5.0–9.5 10.0–14.5 15.0–19.5 20.0–24.5 25.0–29.5 30.0–34.5 35.0–39.5

M3: 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

2(b)(i) Correctly calculates: 1

50  4.18  T
AND
answer to 2–4 sf

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Question Answer Marks

2(b)(ii) Correctly calculates: 1

amount of FA 3 = 0.05  1.0 = 0.050 mol
AND
amount of FA 4 = candidate’s mass / 24.3
AND
FA 3 / CuSO4 is in excess

2(b)(iii) M1 Correctly uses: 2

H = (b)(i) / (1000  n(FA 4) from 2(b)(ii))

M2 sign is negative
AND
answer to 2–4 sf

2(c) M1 Measure the temperature of FA 3 (at regular intervals and) before adding FA 4 3
AND
(Stir the mixture and) measure the temperature of the mixture at regular intervals after adding FA 4 until temperature is
steady or decreasing

M2 Plot a graph of temperature against time

AND
point of addition of FA 4 must be given in text or clearly shown/labelled on sketch graph

M3 extrapolate lines of best fit to find T (max) or T at time of addition (of FA 4)

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Question Answer Marks

3(a) FA 5 is Na2S2O3 ; FA 6 is H2SO4 FA 7 is Na2SO3 FA 8 is Cu2O

11 * observations 5
2* = 1 mark (round down)

observations
test
FA 5 FA 6 FA 7

Test 1 *purple (solution) / MnO4−/ *no change / (MnO4–) stays *purple (solution) / MnO4− /
KMnO4 purple / does not decolourise KMnO4
and (KMnO4) and
turns colourless / decolourised turns colourless / decolourised

*white / off-white / cream / pale *no change no change

yellow ppt forms and

Test 2 *no change *effervescence / bubbling / *no change

and fizzing

*(gas) pops with a lighted splint

Test 3 no change *white ppt *white ppt

3(b)(i) FA 5 is S2O32− ; FA 6 is SO42− FA 7 is SO32− 2

2 correct = 1 mark
3 correct = 2 marks

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Question Answer Marks

3(b)(ii) M1 Cation is H+ 2
AND
chooses Na2CO3 / sodium carbonate / other named carbonate or named indicator

M2 effervescence / fizzing / bubbling or suitable indicator colour

AND
gas / CO2 gives a white ppt with limewater / suitable indicator colours before and after use, e.g. blue litmus goes red

3(c) Mg(s) + 2H+(aq) → Mg2+(aq) + H2(g) 1

or
Ba2+(aq) + SO42−(aq) → BaSO4(s)
or
Ba2+(aq) + SO32−(aq) → BaSO3(s)

3(d)(i) Residue: red-brown / brown / pink / pink-brown (solid) 1

AND
filtrate: (pale) blue (solution)

3(d)(ii) Brown / yellow-brown / orange-brown / red-brown (mixture) 1

3(d)(iii) (On addition of NaOH) blue ppt insoluble in excess 1

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