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Cambridge International AS & A Level
CHEMISTRY 9701/32
Paper 3 Advanced Practical Skills 2 May/June 2022
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 for
Teachers.
Cambridge International will not enter into discussions about these mark schemes.
Cambridge International is publishing the mark schemes for the May/June 2022 series for most
Cambridge IGCSE, Cambridge International A and AS Level and Cambridge Pre-U components, and some
Cambridge O Level components.
This document consists of 11 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 descriptors 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 All the following data are recorded: 7
two burette readings and titre for the rough titration
initial and final burette readings for two (or more) accurate titrations
II Correct headings and units in the accurate titration table and titre values recorded for accurate titrations
initial / start and (burette) reading / volume + unit
final / end and (burette) reading / volume + unit
titre + unit or volume / FB 1 and used / added + unit
III All accurate burette readings are recorded to the nearest 0.05 cm3
IV The final accurate titre recorded is within 0.10 cm3 of any other accurate titre
For assessment of accuracy marks, round all burette readings to the nearest 0.05 cm3. Check and correct subtractions.
Then select the ‘best’ titres using the hierarchy:
two (or more) accurate identical titres (ignoring any that are labelled ‘rough’), then
two (or more) accurate titres within 0.05 cm3, then
two (or more) accurate titres within 0.10 cm3, etc.
These best titres should be used to calculate the mean titre, expressed to nearest 0.01 cm3. Write the candidate’s mean
titre on each script.
Write the Supervisor’s [corrected] mean titre in a ring on each candidate script.
Calculate the difference () between the candidate’s mean titre and the supervisor’s mean titre.
Write the value of on each script.
Award the accuracy marks as shown below.
1(a) Award V if ⩽ 0.50 (cm3)
Award VI if ⩽ 0.30
Award VII if ⩽ 0.20
1(b) Correctly calculates the mean titre correct to 2 dp from accurate titres that are within 0.20 cm3 total spread 1
1(c)(i) All final answers for (c)(ii), (c)(iii), and (c)(iv) are to 3–4 sf 1
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Question Answer Marks
1(c)(ii) Correctly calculates 1
n(NaOH) = 0.1 (b) / 1000
AND
n(NaHSO4) = same answer
1(c)(iii) Correctly uses 1
[NaHSO4] = final answer (c)(ii) 1000 / 25 (= (c)(ii) 40)
AND
answer above 120.1
1(c)(iv) Correctly uses 1
final answer (c)(ii)
% NaHSO4 =
12.53 100
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Question Answer Marks
2(a) I Ten thermometer readings recorded, all shown to .0 or .5 ºC 3
AND at least one reading at .0 and one at .5
For assessment of accuracy marks, round all thermometer readings to the nearest 0.5 °C.
Calculate the supervisor’s greatest T (= Tmax – Tinitial) and write it ringed on each candidate script. Note volume (V) at
which the Tmax occurs.
Calculate the candidate’s T at the same volume (= Tat V – Tinital) then calculate the difference, , from the supervisor value.
Award of accuracy marks
For supervisor T 10.0 – 20.0:
II Award if ⩽2.0 ºC
III Award if ⩽1.0 ºC
2(b)(i) I Axes unambiguously labelled 4
temperature or °C on y-axis
AND
volume / FB 5 / H2SO4 / acid or cm3 on the x-axis
AND
some numbers for scales
II Suitable scales chosen
III All points recorded in the table are accurately plotted
IV Lines of best fit drawn (straight or smoothly curved lines)
AND
extrapolated to intersect
2(b)(ii) Correct volume from suitable intersect to 1 or 2 dp 1
AND
correct T to 1 dp
2(c)(i) Correctly calculates 1
n(H2SO4) = 1.00 volume (b)(ii) / 1000
AND
answer to 2–4 significant figures
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Question Answer Marks
2(c)(ii) Correctly calculates 1
Q = (25 + V(b)(ii)) 4.18 T(b)(ii)
and
answer to 2–4 sf
2(c)(iii) Correctly uses 1
(c)(ii)
H = / (1000)
2 (c)(i)
AND answer given to minimum 2 sf
AND units kJ mol−1 or J mol−1 to match use or absence of ÷ 1000
AND negative sign
2(d)(i) Correct expression 1
[(− 57.6 – (c)(iii)) / 57.6] 100
OR
[((c)(iii) – (– 57.6)) / 57.6] 100
2(d)(ii) take more readings (near the end point) AND to improve position of intersection / owtte 1
2(e)(i) Correctly uses 1
1000
n(NaOH) = (c)(i) 2
25
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Question Answer Marks
2(e)(ii) I Correctly uses 2
(e)(i)
20
AND
answer to 2 or more sf
II Explanation matches answer
If conc NaOH > 0.1 mol dm−3 then 1st box ticked
and (titre remains unchanged so actual) mol NaOH↑ so mol / amount / mass NaHSO4↑
OR
If conc NaOH approx. 0.1 mol dm−3 then 2nd box ticked
and titre not / (only) slightly changed so within experimental error
OR
If conc NaOH < 0.1 mol dm−3 then 3rd box ticked
and (titre remains unchanged so actual) mol NaOH↓ so mol / amount / mass NaHSO4↓
OR
If conc NaOH < 0.1 mol dm−3 then 1st box ticked
and larger titre so moles / amount / mass NaHSO4 calculated increases
OR
If conc NaOH > 0.1 mol dm−3 then 3rd box ticked
and smaller titre so mol / amount / mass NaHSO4 calculated decreases
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Question Answer Marks
FB 6 is KI(s); FB 7 is MnCl 2 + NH4Cl (aq); FB 8 is FeSO4
3(a) I Suitable reagents for anion
One of:
If testing for carbonate:
I named (dilute) acid (and limewater)
II description of testing gas with limewater
III no effervescence / no fizzing / no change
IV unknown (provided test carried out and no contradictory result)
OR
If testing for halide:
I (aqueous) AgNO3 and NH3
II use a solution of FB 6
III (pale) yellow ppt, insoluble in NH3
IV I– (must be from (pale) yellow ppt)
OR
If testing for nitrate / nitrite :
I sodium hydroxide and Al
II warm in a boiling tube
III gas does not turn litmus blue / red litmus stays red
IV unknown (provided test carried out and no contradictory result)
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Question Answer Marks
3(b)(i) 4
FB 7 FB 8
+ H+/ MnO4− turns brown OR purple (solution) / KMnO4 / MnO4– AND
brown solution OR decolourised / turns yellow / turns colourless *
(dark) brown ppt *
+ NH3 off-white / pale brown ppt AND green ppt AND
insoluble in excess OR darkens / turns dark(er) insoluble in excess OR turns brown / red-brown /
brown * rust (on standing) *
+ NaOH off-white / pale brown ppt AND green ppt AND
insoluble in excess OR darkens / turns dark(er) insoluble in excess OR turns brown / red-brown /
brown * rust (on standing) *
& warm gas / NH3 turns (damp red) litmus blue * no (visible) reaction / no change *
2 * = 1 mark
3(b)(ii) FB 7: Mn2+ and NH4+ 2
FB 8: Fe2+
3 cations correct = 2 marks
2 cations correct = 1 mark
3(b)(iii) One of: 1
Mn2+(aq) + 2OH−(aq) → Mn(OH)2(s)
Fe2+(aq) + 2OH−(aq) → Fe(OH)2(s)
3(b)(iv) Redox / oxidation AND reduction (of manganate(VII)) 1
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