Cambridge A Level Chemistry 9701 — 2025 Oct/Nov Paper 3 · Variant 3

This document has 16 pages. Any blank pages are indicated. [Turn over Cambridge International AS & A Level CHEMISTRY 9701/33 Paper 3 Advanced Practical Skills 1 October/November 2025 2 hours You must answer on the question paper. You will need: The materials and apparatus listed in the confidential instructions Insert (enclosed) INSTRUCTIONS ● Answer all questions. ● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. ● Write your name, centre number and candidate number in the boxes at the top of the page. ● Write your answer to each question in the space provided. ● Do not use an erasable pen or correction fluid. ● Do not write on any bar codes. ● You may use a calculator. ● You should show all your working and use appropriate units. INFORMATION ● The total mark for this paper is 40. ● The number of marks for each question or part question is shown in brackets [ ]. ● The Periodic Table is printed in the question paper. ● Important values, constants and standards are printed in the question paper. ● Notes for use in qualitative analysis are provided in the question paper. * 2 4 9 6 0 4 8 0 0 0 * DC (CJ/SW) 341130/2 © UCLES 2025 Session Laboratory For Examiner’s Use 1 2 3 Total ,










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3 9701/33/O/N/25 © UCLES 2025 [Turn over Quantitative analysis Read through the whole method before starting any practical work. Where appropriate, prepare a table for your results in the space provided. Show the precision of the apparatus you used in the data you record. Show your working and appropriate significant figures in the final answer to each step of your calculations. 1 The thiosulfate ion, S2O3 2–, decomposes when an acid is added. S2O3 2–(aq) + 2H+(aq) S(s) + SO2(aq) + H2O(l) The rate of this reaction can be investigated by measuring how long it takes for the solid sulfur forming to obscure the print on the insert. You will investigate how the concentration of the thiosulfate ion affects the rate of the reaction. Note: A small amount of sulfur dioxide gas may be formed in the experiment. It is very important that you avoid inhaling any fumes. As soon as each experiment is complete, add the reaction mixture to the quenching bath and rinse the beaker thoroughly. FA 1 is 0.100 mol dm–3 sodium thiosulfate, Na2S2O3. FA 2 is 2.00 mol dm–3 hydrochloric acid, HCl. (a) Method Experiment 1 • Fill a burette with FA 1. • Run 40.00 cm3 of FA 1 into the 100 cm3 beaker. • Use the 25 cm3 measuring cylinder to measure 10.0 cm3 of FA 2. • Add the FA 2 to the FA 1 in the beaker and start timing immediately. • Stir the mixture once and place the beaker on the printed insert. • View the printing on the insert from above through the solution. • Stop timing when the print on the insert becomes obscured. • Record this reaction time to the nearest second in the space for results. • Empty the contents of the beaker into the quenching bath. • Rinse and dry the beaker so it is ready to use in Experiment 2. Experiment 2 • Refill the burette with FA 1. • Fill the second burette with distilled water. • Run 20.00 cm3 of FA 1 into the 100 cm3 beaker. • Run 20.00 cm3 of distilled water into the same beaker. • Use the 25 cm3 measuring cylinder to measure 10.0 cm3 of FA 2. • Add the FA 2 to the FA 1 in the beaker and start timing immediately. • Stir the mixture once and place the beaker on the printed insert. • View the printing on the insert from above through the solution. • Stop timing when the print on the insert becomes obscured. • Record this reaction time to the nearest second in the space for results. • Empty the contents of the beaker into the quenching bath. • Rinse and dry the beaker so it is ready to use in the next experiment. * 0000800000003 * ,










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4 9701/33/O/N/25 © UCLES 2025 Experiments 3–5 • Carry out three further experiments to investigate how using different volumes of FA 1 affects the reaction time. Note: the combined volumes of FA 1 and distilled water must always be 40.00 cm3. Do not use a volume of FA 1 that is less than 15.00 cm3. Record all your results in a table. You should include the volume of FA 1, the volume of distilled water, the reaction time and the reaction rate for each of your five experiments. The rate of reaction can be calculated using the following formula. rate = 1000 reaction time Results [8] (b) (i) On the grid in Fig. 1.1, plot the rate (y-axis) against the volume of FA 1 (x-axis). Start each axis at the origin (0, 0). Ring any anomalous points. Draw a line of best fit. I II III IV V VI VII VIII * 0000800000004 * ,










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5 9701/33/O/N/25 © UCLES 2025 [Turn over Fig. 1.1 [3] I II III * 0000800000005 * ,










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6 9701/33/O/N/25 © UCLES 2025 (ii) Use your graph in Fig. 1.1 to determine the time it would take for the print to be obscured if 7.50 cm3 of FA 1, 32.50 cm3 of water and 10.0 cm3 of FA 2 had been used. Show clearly on the graph how you worked out your answer. time for printing to be obscured = … s [2] (c) A student carries out the same method as given in (a) but using a different concentration of acid. The student’s calculated values for the rate are plotted on the grid in Fig. 1.2. 0.00 0 10 20 30 40 50 60 5.00 10.00 15.00 20.00 25.00 volume of FA 1 rate vs volume of FA 1 30.00 35.00 40.00 45.00 rate Fig. 1.2 State whether the student’s results show that the rate is directly proportional to the volume of FA 1 used. Explain your answer. … … [2] [Total: 15] * 0000800000006 * ,










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8 9701/33/O/N/25 © UCLES 2025 2 When hydrated sodium thiosulfate is dissolved in water the temperature of the liquid changes. You will carry out an experiment to determine the enthalpy change, ΔH, when one mole of hydrated sodium thiosulfate dissolves in water. FA 3 is hydrated sodium thiosulfate, Na2S2O3•5H2O. (a) Method • Support the cup in the 250 cm3 beaker. • Use the 50 cm3 measuring cylinder to transfer 30.0 cm3 of distilled water into the cup. • Measure the temperature of the water in the cup. Record this in the space for results. • Weigh the container with FA 3. Record the mass. • Tip all the FA 3 into the cup. • Stir the mixture until the minimum temperature is obtained. Record this temperature. • Weigh the container with any residual FA 3. Record the mass. • Calculate and record the mass of FA 3 added. • Calculate and record the temperature change. Results [4] (b) Calculations (i) Calculate the amount, in mol, of hydrated sodium thiosulfate added. amount of Na2S2O3•5H2O = … mol [1] (ii) Calculate the energy change, in J, in your experiment. energy change = … J [1] I II III IV * 0000800000008 * ,










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9 9701/33/O/N/25 © UCLES 2025 [Turn over (iii) Calculate the enthalpy change, ΔH, in kJ mol−1, when 1.00 mol of hydrated sodium thiosulfate dissolves in water. Show your working. ΔH = … … kJ mol−1 sign value [1] (c) The value calculated in (b)(iii) can be used to determine the enthalpy change, ΔHr , for the following reaction. Na2S2O3(s) + 5H2O(l) Na2S2O3•5H2O(s) Outline the method of one further experiment you would need to carry out to obtain the data necessary to calculate the value of ΔHr . Show how you would use your results from this experiment and (b)(iii) to calculate ΔHr . Do not carry out your experiment. method … … … calculation … … [4] [Total: 11] * 0000800000009 * ,










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10 9701/33/O/N/25 © UCLES 2025 Qualitative analysis For each test you should record all your observations in the spaces provided. Examples of observations include: • colour changes seen • the formation of any precipitate and its solubility (where appropriate) in an excess of the reagent added • the formation of any gas and its identification (where appropriate) by a suitable test. You should record clearly at what stage in a test an observation is made. Where no change is observed, you should write ‘no change’. Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. If any solution is warmed, a boiling tube must be used. If a solid is heated, a hard-glass test-tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests should be attempted. 3 Half-fill the 250 cm3 beaker with water and place it on a tripod and gauze. Heat the water until boiling then switch off your Bunsen burner. This will be your hot water bath for use in (b)(i). Start (a)(i) while the water is heating. (a) FA 4 is an aqueous solution containing three ions. One ion is not listed in the Qualitative analysis notes. FA 5 is an aqueous solution containing two ions. The cation in FA 5 is listed in the Qualitative analysis notes. The anions in both FA 4 and FA 5 contain sulfur. (i) Carry out the following tests using a 1 cm depth of either FA 4 or FA 5 in a test-tube. Record your observations in Table 3.1. * 0000800000010 * ,










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11 9701/33/O/N/25 © UCLES 2025 [Turn over Table 3.1 test observations FA 4 FA 5 Test 1 Add aqueous sodium hydroxide. Test 2 Add aqueous ammonia. Test 3 Add aqueous sodium carbonate. Test 4 Add aqueous barium chloride or aqueous barium nitrate. Test 5 Add acidified aqueous potassium manganate(VII). [5] (ii) From your observations in (a)(i), deduce the identities of the ions present in FA 4 and FA 5. Give the formula of each ion in Table 3.2. If you are unable to identify an ion write ‘unknown’. Table 3.2 ions present FA 4 FA 5 cations anions [3] * 0000800000011 * ,









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12 9701/33/O/N/25 © UCLES 2025 (b) (i) Both FA 6 and FA 7 are one of propan-1-ol, propan-2-ol, methanoic acid or ethanoic acid. You will carry out tests to investigate the identities of FA 6 and FA 7. For each test use a 1 cm depth of FA 6 or FA 7 in a test-tube. Record your observations in Table 3.3. Table 3.3 test observations FA 6 FA 7 Test 1 Add a few drops of acidified aqueous potassium manganate(VII), then place the test-tube in the hot water bath. Test 2 Add a 2 cm depth of aqueous iodine followed by drops of aqueous sodium hydroxide until the colour just disappears. If no reaction is visible, place the test-tube in the hot water bath. Test 3 Add aqueous sodium carbonate. [3] (ii) From your observations in (b)(i) deduce the identities of FA 6 and FA 7. Give reasons for your answers. FA 6 is … reasons … … FA 7 is … reasons … … [2] * 0000800000012 * ,









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13 9701/33/O/N/25 © UCLES 2025 (c) A student carrying out a similar set of tests identifies two unknown compounds to be ethanol and propanoic acid. Write an equation for the reaction between these two compounds. … [1] [Total: 14] * 0000800000013 * ,









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14 9701/33/O/N/25 © UCLES 2025 Qualitative analysis notes 1 Reactions of cations cation reaction with NaOH(aq) NH3(aq) aluminium, Al 3+(aq) white ppt. soluble in excess white ppt. insoluble in excess ammonium, NH4 +(aq) no ppt. ammonia produced on warming – barium, Ba2+(aq) faint white ppt. is observed unless [Ba2+(aq)] is very low no ppt. calcium, Ca2+(aq) white ppt. unless [Ca2+(aq)] is very low no ppt. chromium(III), Cr3+(aq) grey-green ppt. soluble in excess giving dark green solution grey-green ppt. insoluble in excess copper(II), Cu2+(aq) pale blue ppt. insoluble in excess pale blue ppt. soluble in excess giving dark blue solution iron(II), Fe2+(aq) green ppt. turning brown on contact with air insoluble in excess green ppt. turning brown on contact with air insoluble in excess iron(III), Fe3+(aq) red-brown ppt. insoluble in excess red-brown ppt. insoluble in excess magnesium, Mg2+(aq) white ppt. insoluble in excess white ppt. insoluble in excess manganese(II), Mn2+(aq) off-white ppt. rapidly turning brown on contact with air insoluble in excess off-white ppt. rapidly turning brown on contact with air insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions anion reaction carbonate, CO3 2– CO2 liberated by dilute acids chloride, Cl –(aq) gives white ppt. with Ag+(aq) (soluble in NH3(aq)) bromide, Br –(aq) gives cream / off-white ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I–(aq) gives pale yellow ppt. with Ag+(aq) (insoluble in NH3(aq)) nitrate, NO3 –(aq) NH3 liberated on heating with OH–(aq) and Al foil nitrite, NO2 –(aq) NH3 liberated on heating with OH–(aq) and Al foil; decolourises acidified aqueous KMnO4 sulfate, SO4 2–(aq) gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids); gives white ppt. with high [Ca2+(aq)] sulfite, SO3 2–(aq) gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids); decolourises acidified aqueous KMnO4 thiosulfate, S2O3 2–(aq) gives off-white/pale yellow ppt. slowly with H+ * 0000800000014 * ,









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15 9701/33/O/N/25 © UCLES 2025 3 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 gives a white ppt. with limewater hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint 4 Tests for elements element test and test result iodine, I2 gives blue-black colour on addition of starch solution 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) * 0000800000015 * ,









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16 9701/33/O/N/25 © UCLES 2025 To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Group The Periodic Table of Elements 1 H hydrogen 1.0 2 He helium 4.0 1 2 13 14 15 16 17 18 3 4 5 6 7 8 9 10 11 12 3 Li lithium 6.9 4 Be beryllium 9.0 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23.0 12 Mg magnesium 24.3 19 K potassium 39.1 20 Ca calcium 40.1 37 Rb rubidium 85.5 38 Sr strontium 87.6 55 Cs caesium 132.9 56 Ba barium 137.3 87 Fr francium – 88 Ra radium – 5 B boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 81 Tl thallium 204.4 6 C carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sn tin 118.7 82 Pb lead 207.2 22 Ti titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium 178.5 104 Rf rutherfordium – 23 V vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium – 24 Cr chromium 52.0 42 Mo molybdenum 95.9 74 W tungsten 183.8 106 Sg seaborgium – 25 Mn manganese 54.9 43 Tc technetium – 75 Re rhenium 186.2 107 Bh bohrium – 26 Fe iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium – 27 Co cobalt 58.9 45 Rh rhodium 102.9 77 Ir iridium 192.2 109 Mt meitnerium – 28 Ni nickel 58.7 46 Pd palladium 106.4 78 Pt platinum 195.1 110 Ds darmstadtium – 29 Cu copper 63.5 47 Ag silver 107.9 79 Au gold 197.0 111 Rg roentgenium – 30 Zn zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200.6 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14.0 15 P phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 83 Bi bismuth 209.0 8 O oxygen 16.0 16 S sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium – 9 F fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 53 I iodine 126.9 85 At astatine – 10 Ne neon 20.2 18 Ar argon 39.9 36 Kr krypton 83.8 54 Xe xenon 131.3 86 Rn radon – 113 Nh nihonium – 115 Mc moscovium – 117 Ts tennessine – 118 Og oganesson – 21 Sc scandium 45.0 39 Y yttrium 88.9 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 138.9 89 Ac lanthanoids actinoids actinium – 58 Ce cerium 140.1 90 Th thorium 232.0 59 Pr praseodymium 140.9 91 Pa protactinium 231.0 60 Nd neodymium 144.2 92 U uranium 238.0 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150.4 94 Pu plutonium – 63 Eu europium 152.0 95 Am americium – 64 Gd gadolinium 157.3 96 Cm curium – 65 Tb terbium 158.9 97 Bk berkelium – 66 Dy dysprosium 162.5 98 Cf californium – 67 Ho holmium 164.9 99 Es einsteinium – 68 Er erbium 167.3 100 Fm fermium – 69 Tm thulium 168.9 101 Md mendelevium – 70 Yb ytterbium 173.1 102 No nobelium – 71 Lu lutetium 175.0 103 Lr lawrencium – * 0000800000016 * ,









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This document consists of 14 printed pages. © Cambridge University Press & Assessment 2025 [Turn over Cambridge International AS & A Level CHEMISTRY 9701/33 Paper 3 Advanced Practical Skills 1 October/November 2025 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 October/November 2025 series for most Cambridge IGCSE, Cambridge International A and AS Level components, and some Cambridge O Level components.

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 2 of 14 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 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.

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 3 of 14 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 thre sholds 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 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 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.

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 4 of 14 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.

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 5 of 14 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 standard isation 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 Information missing or insufficient for credit Benefit of the doubt given Contradiction in response otherwise markworthy, mark not given Error in number of decimal places Error carried forward applied Incorrect or insufficient point ignored while marking the rest of the response Rounding error Repeat error or / Blank page or part of script seen

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 6 of 14 Annotation Meaning Error in number of significant figures Transcription error

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 7 of 14 Mark Scheme abbreviations ; separates marking points / alternative responses for the same marking point R reject the response A accept the response I ignore the response ecf error carried forward AVP any valid point ora or reverse argument AW alternative wording underline actual word given must be used by candidate (grammatical variants excepted) ( ) the word / phrase in brackets is not required but sets the context max indicates the maximum number of marks that can be given M1 etc. marking point owtte or words to that effect

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 8 of 14 Question Answer Marks 1(a) I Five experiments completed AND Table to show Volume of FA 1, Volume of water, Time and Rate 1 II Correct units for all data Volume: / cm3 OR (cm3) OR in cm3 OR cm3 by each volume Time: / s OR (s) OR in s OR s by each time Rate: / s–1 OR (s–1) OR in s–1 OR s–1 by each rate 1 III All times recorded to nearest second AND Volumes of FA 1 and water both given 2 d.p. ending with 0 or 5 1 IV Three additional experiments with volume FA 1 ⩾ 15.00 cm3, < 40.00 cm3 and no volume closer than 5.00 cm3 to another volume. AND Volumes of water chosen so that total volume = 40.00 cm3 for additional experiments. 1 V Correctly calculates rate for all experiments and shown to 2 – 4 s.f. 1 VI Award if all times recorded increase with decreasing volume of FA 1. 1 Examiner corrects time for VFA1 = 40.00 cm3 and VFA1 = 20.00 cm3 to the nearest s then calculates 20 40 / t t to 2 d.p. VII Award if candidate’s ratio is within the range 1.80 to 2.30. 1 VIII Award if candidate’s ratio is within the range 1.90 to 2.20. 1

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 9 of 14 Question Answer Marks 1(b)(i) l Unambiguous labelled axes with rate on the y-axis and volume of FA 1 on the x-axis OR correct units AND suitable linear scales starting at (0,0). 1 II Points plotted correctly. 1 III Line of best fit drawn, straight line or smooth curve, that ignores anomalous results identified by the candidate. 1 1(b)(ii) M1 Correct line(s) drawn AND Rate correctly read within half a small square. M2 1000 / rate AND correctly calculates answer to 2 – 4 s.f. 2 1(c) M1 Correct line of best fit M2 (Rate and volume of FA 1 are) not directly proportional as the (straight) line / data / results does not / do not pass through the origin / (0,0) OR M1 unavailable for line of best fit through the origin. M2 (Rate and volume of FA 1 are) directly proportional as the (straight) line / data / results pass through the origin / (0,0) 2

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 10 of 14 Question Answer Marks 2(a) I 6 correct unambiguous headings shown, with units, in list / table • (mass of) container + FA 3 / solid / Na2S2O3•5H2O • (mass of) container (empty OR with residual FA 3) • (mass of) FA 3 / solid / Na2S2O3•5H2O OR mass used OR mass added • initial temperature / thermometer reading • lowest / minimum / final temperature / thermometer reading • temperature change / decrease Mass units: /g OR in g OR (g) OR g by every reading Temperature units: / °C OR in °C OR (°C) OR °C by every reading 1 II All readings shown to appropriate precision • all four balance / thermometer readings shown • both thermometer readings to .0 OR .5 • both weighings consistently to either 2 d.p. OR to 3 d.p. 1 III Subtractions correctly calculated • mass of solid correct AND temperature change correct 1 IV T is within 1.0 ºC of expected temperature change for the mass used 1 2(b)(i) Correctly calculates amount of FA 3 = mass FA 3 in 2(a) / 248.2 mol AND answer given to 2–4 s.f. 1 2(b)(ii) Correctly calculates energy change = 30  4.18  T J AND answer given to 2 – 4 sf 1

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 11 of 14 Question Answer Marks 2(b)(iii) Correctly uses (b)(ii) / (b)(i)  1000 AND plus sign shown AND answer given to 2 – 4 sf 1 2(c) M1 repeating experiment with Na2S2O3 OR adding Na2S2O3 in water M2 any two from: • known volume of water • known mass of solid • measuring the temperature change. M3 indicating that use of Hess’s law is needed M4 Hr = H from their additional experiment – (b)(iii) 4

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 12 of 14 Question Answer Marks FA 4 is acidified Fe2(SO4)3(aq); FA 5 is Al 2(SO4)3(aq); FA 6 is HCOOH(aq); FA 7 is CH3CH(OH)CH3(l) 3(a)(i) 2 * = 1 mark (round down). Max 5 marks. test observations FA 4 FA 5 1 + NaOH(aq) red-brown / brown ppt AND insoluble in excess * white ppt * soluble in excess * 2 + NH3(aq) red-brown / brown ppt AND insoluble in excess * white ppt AND insoluble in excess * 3 + Na2CO3(aq) fizzing * gas gives white ppt with limewater * red-brown ppt * white ppt * fizzing * gas gives white ppt with limewater (award if not awarded for FA 4) 4 + BaCl 2(aq) / Ba(NO3)2(aq) white ppt AND white ppt * 5 + H+ / KMnO4(aq) stays purple / no change AND stays purple / no change * 5

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 13 of 14 Question Answer Marks 3(a)(ii) ions FA 4 FA 5 cations Fe3+; H+ Al 3+ anions SO42− SO42− 5 ions correct = 3 marks 3 or 4 ions correct = 2 marks 2 ions correct = 1 mark 3 3(b)(i) 2 * = 1 mark (round down) test observations FA 6 FA 7 1 + H+ / KMnO4(aq) (turns paler pink) (purple fades slightly) and warm decolourises / turns colourless / turns (pale) yellow * decolourises / turns colourless / turns (pale) yellow * 2 + I2(aq) + NaOH (and warm) no change * ppt * that is (pale) yellow * 3 + Na2CO3(aq) fizzing * no change * 3

9701/33 Cambridge International AS & A Level – Mark Scheme PUBLISHED October/November 2025 © Cambridge University Press & Assessment 2025 Page 14 of 14 Question Answer Marks 3(b)(ii) M1 (FA 6 is) methanoic acid because it produces CO2 / reacts with sodium carbonate AND it can be oxidised / it reacts with KMnO4 M2 (FA 7 is) propan-2-ol as it gives a ppt in test 2 OR gives a positive tri-iodomethane/iodoform test OR has the −CH(OH)CH3 group 2 3(c) Correct equation CH3CH2COOH + CH3CH2OH → CH3CH2COOCH2CH3 + H2O OR C2H5COOH + C2H5OH → C2H5COOC2H5 + H2O 1