Chemistry 9701/52 October/November 2025: question paper and mark scheme
Cambridge AS & A Level Chemistry (9701), Paper 5 Planning, Analysis and Evaluation, October/November 2025. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.
Aqueous silver ions, Ag+(aq), react slowly with aqueous iron(II) ions, Fe2+(aq). An equilibrium is established.
Ag+(aq) + Fe2+(aq) Ag(s) + Fe3+(aq)
The concentration of Ag+(aq) at equilibrium can be determined by titration with a standard solution of aqueous potassium thiocyanate, KSCN(aq).
During the titration, the remaining Ag+(aq) ions react with SCN–(aq) ions to form a precipitate of
AgSCN(s).
Ag+(aq) + SCN–(aq) AgSCN(s)
When all Ag+(aq) ions have been removed from solution, excess SCN–(aq) ions react with Fe3+(aq) to form a complex ion, FeSCN2+(aq), which has a red colour.
Fe3+(aq) + SCN–(aq) FeSCN2+(aq)
The appearance of the red colour indicates the end-point.
A student carries out an experiment to determine the equilibrium constant, Kc.
[Fe3+(aq)]eqm
Kc =
[Fe2+(aq)]eqm [Ag+(aq)]eqm
The student makes 250.0 cm3 of 0.0200 mol dm–3 KSCN(aq) to use in the titration.
(a) Calculate the mass of solid potassium thiocyanate, KSCN(s), needed to make 250.0 cm3 of
0.0200 mol dm–3 KSCN(aq).
mass of KSCN(s) = …… g [1]
* 0000800000003 * DFD
3
(b) Describe how the student should make 250.0 cm3 of 0.0200 mol dm–3 KSCN(aq) starting from the mass of KSCN(s) calculated in (a) in a 50 cm3 beaker.
Give the name and size of any key apparatus used.
Write your answer using a series of numbered steps.
…… [3]
(c) The student uses the following method to determine Kc.
step 1 Add 25.0 cm3 of 0.100 mol dm–3 aqueous silver nitrate, AgNO3(aq), into a dry conical flask. Label this flask A.
step 2 Add 25.0 cm3 of 0.100 mol dm–3 aqueous iron(II) sulfate, FeSO4(aq), into flask A.
step 3 Seal flask A, using a bung.
step 4 Allow flask A to stand for twelve hours.
step 5 Transfer 10.0 cm3 of the mixture from flask A into another conical flask, flask B, without disturbing the precipitate in flask A.
step 6 Titrate the sample in flask B with 0.0200 mol dm–3 aqueous potassium thiocyanate,
KSCN(aq).
step 7 Repeat steps 5 and 6 until concordant values are obtained.
(i) Suggest why flask A is sealed with a bung in step 3.
…… [1]
(ii) Suggest why flask A is left to stand for twelve hours in step 4.
…… [1]
(iii) Identify the precipitate in flask A in step 5.
…… [1]
* 0000800000004 * DFD
4
(d) The student’s results are shown in Table 1.1
Table 1.1
rough titration 1 titration 2 titration 3 titration final burette
22.50 21.75 31.65 32.20 reading / cm3 initial burette
0.00 0.00 9.75 10.20
reading / cm3
titre / cm3 22.50 21.75 21.90 22.00
(i) State if concordant titres have been achieved.
Explain your answer.
…… [1]
(ii) Calculate the percentage error in the titre volume in titration 2.
Show your working.
percentage error = …… [1]
(iii) The student repeats the experiment using KSCN(aq) at a higher concentration. The student obtains smaller titres.
Suggest one reason why a larger titre is better than a smaller titre.
…… [1]
* 0000800000005 * DFD
5
(e) Another student calculates a mean titre of 21.85 cm3. Use this value to complete the following calculation.
(i) Calculate [Ag+(aq)] in the equilibrium mixture in flask A.
[Ag+(aq)]eqm = …… mol dm–3 [1]
(ii) Calculate [Fe3+(aq)] in the equilibrium mixture in flask A.
[Fe3+(aq)]eqm = …… mol dm–3 [1]
(iii) The formula for the equilibrium constant, Kc, is shown.
[Fe3+(aq)]eqm
Kc =
[Fe2+(aq)]eqm [Ag+(aq)]eqm
Determine the value of Kc.
Give the units of Kc.
Kc = ……
units ……
[2]
* 0000800000006 * DFD
6
(f) Several other students perform the same experiment at different temperatures. The Kc values that they obtain are used to produce the graph in Fig. 1.1.
3.5
3.4
3.3
3.2
3.1
Kc
3.0
/ units not shown
2.9
2.8
2.7
2.6
2.5
280 300 320 340 360 380 temperature / K
Fig. 1.1
(i) One student suggests that Kc is directly proportional to temperature.
State and explain if the results displayed in Fig. 1.1 support this suggestion.
…… [1]
(ii) Another student suggests that the data represented in the graph in Fig. 1.1 is reliable.
Explain how the graph supports this suggestion.
…… [1]
* 0000800000007 * DFD
7
(iii) Use the data displayed in Fig. 1.1 to state if the forward reaction is exothermic or endothermic.
Ag+(aq) + Fe2+(aq) Ag(s) + Fe3+(aq)
Explain your answer.
forward reaction ……
explanation ……
[1]
[Total: 17]
DFD
8
* 0000800000009 * DFD
9
Mark scheme
1(a) 0.486 g 1
1(b) M1 Dissolve the solid / KSCN(s) in (the beaker) (using a small volume of) (distilled) water 3
M2 Transfer/add to a (250 cm3 volumetric) flask
and
Rinse (with distilled water)
M3 Top the 250 cm3 volumetric flask up to mark (with distilled water)
and
Invert the (stoppered) flask
Allow ‘250 volumetric flask’ (i.e. units need not be seen)
1(c)(i) to avoid oxidation (of contents of flask) 1
1(c)(ii) to ensure that equilibrium has been reached 1
1(c)(iii) Silver / Ag 1
1(d)(i) (yes) 1
and
two titres (2 and 3) are within 0.10 cm³ (of each other)
1(d)(ii) Working must be shown 1
2× 0.05
= × 100 = 0.457%
21.90
1(d)(iii) percentage error (in larger titre) is lower 1
1(e)(i) 0.0437 mol dm–3 1
1(e)(ii) 0.00630 mol dm–3 1
1(e)(iii) M1 Kc = 0.00630 / (0.04370) 2 = 3.30 1
M2 units = dm3 mol–1 1
1(f)(i) No 1
and
As temperature increases, Kc decreases
1(f)(ii) (data points that obey a line of best fit are reliable because) there are no anomalous points. 1
1(f)(iii) exothermic 1
and
As temperature increases:
Kc decreases
or
equilibrium shifts to left
A student carries out an experiment to determine the concentration of aqueous sulfate ions,
SO42–(aq), in a sample of lake water.
(a) The student uses the following method.
step 1 Transfer 25.00 cm3 of the lake water sample to a beaker and record its conductivity as shown in Fig. 2.1.
step 2 Add 5.00 cm3 of 0.100 mol dm–3 aqueous barium hydroxide, Ba(OH)2(aq), to the beaker.
step 3 Stir the mixture and record the conductivity of the contents of the beaker as shown in
Fig. 2.1.
step 4 Repeat steps 2 and 3 until a total of 40.00 cm3 of 0.100 mol dm–3 Ba(OH)2(aq) has been added to the beaker.
conductivity meter
0.0
Fig. 2.1
(i) Suggest a suitable piece of apparatus to transfer 25.00 cm3 of the lake water sample to the beaker in step 1.
…… [1]
(ii) 0.100 mol dm–3 Ba(OH)2(aq) is an irritant to skin and eyes. Other than wearing safety goggles, state one safety precaution that the student should take when conducting this experiment.
…… [1]
* 0000800000010 * DFD
10
(b) The student’s results are given in Table 2.1.
A correction can be applied to the conductivity values to take into account dilution of the solution as its volume increases using the following equation.
(total volume in beaker) corrected conductivity = measured conductivity ×
25.00
Table 2.1
volume of
0.100 mol dm–3
measured corrected reading total volume in
Ba(OH)2(aq) conductivity conductivity number beaker / cm3 added to / µS cm–1 / µS cm–1 beaker / cm3
1 0.00 25.00 37 000 37 000
2 5.00 23 000 27 600
3 10.00 12 000 16 800
4 15.00 2 300 3 680
5 20.00 5 000
6 25.00 12 000
7 30.00 18 000
8 35.00 21 000
9 40.00 24 500
(i) Complete Table 2.1. [2]
(ii) Identify the independent variable in this experiment.
…… [1]
* 0000800000011 * DFD
11
(c) Plot a graph on the grid in Fig. 2.2 to show the relationship between corrected conductivity and volume of 0.100 mol dm–3 Ba(OH)2 added to beaker.
Use a cross (×) to plot each data point.
Draw a line of best fit using readings 1 to 4 and another line of best fit using readings 5 to 9.
Extend the lines so that they intersect.
70 000
60 000
50 000
40 000 corrected
conductivity
/ μS cm–1
30 000
20 000
10 000
0
0 5 10 15 20 25 30 35 40 volume of 0.100 mol dm–3 Ba(OH)2(aq) added to beaker / cm3
Fig. 2.2
[2]
* 0000800000012 * DFD
12
(d) The point on the graph where the two lines intersect indicates the volume of 0.100 mol dm–3
Ba(OH)2(aq) required to react exactly with the SO42–(aq) present in 25.00 cm3 of lake water being tested.
(i) Use the graph in Fig. 2.2 to determine the volume of 0.100 mol dm–3 Ba(OH)2(aq) required to react exactly with SO42–(aq) in the lake water sample.
volume required = …… cm3 [1]
(ii) The equation for the reaction taking place in the beaker is shown.
Ba2+(aq) + SO42–(aq) BaSO4(s)
Use your answer in (d)(i) to calculate the concentration of SO42–(aq) in the lake water sample.
concentration of SO42–(aq) = …… mol dm–3 [1]
* 0000800000013 * DFD
13
(e) The concentration of SO42–(aq) in a sample of water can also be determined by measuring the mass of precipitate produced when excess Ba(OH)2(aq) is added to the sample.
The student suggests the following method.
step 1 Place 25.0 cm3 of the water sample in a conical flask.
step 2 Add excess 0.100 mol dm–3 Ba(OH)2(aq) to the flask.
step 3 Filter the contents of the flask.
step 4 Dry the residue in a warm oven.
step 5 Measure the mass of residue.
(i) Draw a labelled diagram to describe the arrangement of apparatus that would be needed to complete step 3.
[1]
(ii) Suggest a step that the student should add between steps 3 and 4 to improve this method.
…… [1]
(iii) Describe what the student can do to ensure that the residue weighed in step 5 is completely dry.
…… [1]
(iv) The mass of residue is used to calculate the concentration of SO42–(aq).
Suggest the effect, if any, on the concentration of SO42–(aq) that is calculated if the residue is not completely dried in step 4.
Explain your answer.
effect on concentration of SO42–(aq) calculated ……
explanation ……
[1]
[Total: 13]
DFD
14
* 0000800000015 * DFD
15
Important values, constants and standards
molar gas constant R = 8.31 J K–1 mol–1
Faraday constant F = 9.65 × 104 C mol–1
Avogadro constant L = 6.02 × 1023 mol–1 electronic charge e = –1.60 × 10–19 C molar volume of gas Vm = 22.4 dm3 mol–1 at s.t.p. (101 kPa and 273 K)
Vm = 24.0 dm3 mol–1 at room conditions
ionic product of water Kw = 1.00 × 10–14 mol2 dm–6 (at 298 K (25 °C)) specific heat capacity of water c = 4.18 kJ kg–1 K–1 (4.18 J g–1 K–1)
The Periodic Table of Elements
Group
1 2 13 14 15 16 17 18
1 2
H He hydrogen helium
Key 1.0 4.0
3 4 atomic number 5 6 7 8 9 10
Li Be atomic symbol B C N O F Ne lithium beryllium name boron carbon nitrogen oxygen fluorine neon
6.9 9.0 relative atomic mass 10.8 12.0 14.0 16.0 19.0 20.2
11 12 13 14 15 16 17 18
Na Mg Al Si P S Cl Ar sodium magnesium aluminium silicon phosphorus sulfur chlorine argon
DFD
23.0 24.3 3 4 5 6 7 8 9 10 11 12 27.0 28.1 31.0 32.1 35.5 39.9
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
at www.cambridgeinternational.org after the live examination series.
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton
39.1 40.1 45.0 47.9 50.9 52.0 54.9 55.8 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
16
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon
85.5 87.6 88.9 91.2 92.9 95.9 – 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3
55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 lanthanoids
Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon
132.9 137.3 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 – – –
87 88 89–103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 actinoids
Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson
– – – – – – – – – – – – – – – – –
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium
138.9 140.1 140.9 144.2 – 150.4 152.0 157.3 158.9 162.5 164.9 167.3 168.9 173.1 175.0
89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 actinoids Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium
– 232.0 231.0 238.0 – – – – – – – – – – –
Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download
To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge
Mark scheme
2(a)(i) (25.0 cm3) volumetric pipette 1
2(a)(ii) (wear) chemically resistant gloves 1
2(b)(i) 2
Total volume Corrected
in beaker / conductivity
cm3 / μS cm–1
25.00 37000
30.00 27600
35.00 16800
40.00 3680
45.00 9000
50.00 24000
55.00 39600
60.00 50400
65.00 63700
M1 Total volume in beaker values
M2 Corrected conductivity values
2(b)(ii) volume of 0.100 mol dm–3 Ba(OH)2(aq) added to beaker 1
2(c) M1: all points 1–4 and 5–9 plotted correctly 2
M2: two straight lines of best fit line drawn going through most points.
lines must intersect.
Place M2 tick in ‘V’ of graph
Place M1 tick or cross on left hand side of grid
Place cross (or highlight) against mis-plot
2(d)(i) intersection point volume (read from within grid) 1
2(d)(ii) nSO42– =0.100 × ans (d)(i) / 1000 = mol 1
[SO42–(aq)] = [0.100 × (d)(i) / 1000] / 0.025
2(e)(i) diagram showing labelled filter paper in a labelled (filter) funnel 1
2(e)(ii) wash the residue with distilled water 1
2(e)(iii) heat to constant mass 1
2(e)(iv) higher value 1
and
(water would cause) (measured) mass / amount (of residue) would be greater
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Chemistry 9701/52 for October/November 2025 is out of 30 marks, with 1 hour 15 minutes to answer it, across 2 questions.
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