Cambridge A Level Chemistry 9701 — 2021 May/June Paper 3 · Variant 1

*5033027902* CHEMISTRY 9701/31 Paper 3 Advanced Practical Skills 1 May/June 2021  2 hours You must answer on the question paper. You will need: The materials and apparatus listed in the confidential instructions 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, use appropriate units and use an appropriate number of significant figures. ● Give details of the practical session and laboratory, where appropriate, in the boxes provided. 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. ● Notes for use in qualitative analysis are provided in the question paper. IB21 06_9701_31/4RP © UCLES 2021 [Turn over This document has 16 pages. Any blank pages are indicated. Cambridge International AS & A Level Session Laboratory For Examiner’s Use 1 2 3 Total

2 9701/31/M/J/21 © UCLES 2021 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 your working and appropriate significant figures in the final answer to each step of your calculations. 1 Iron(II) sulfate crystals, FeSO4•xH2O, contain water of crystallisation. You will carry out a titration to determine the value of x in the formula, where x is an integer. A solution containing a known mass of the crystals will be titrated with acidified aqueous potassium manganate(VII) of known concentration. 5Fe2+(aq) + MnO4 –(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l) FA 1 contains 26.52 g dm–3 of hydrated iron(II) sulfate, FeSO4•xH2O. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is dilute sulfuric acid, H2SO4. (a) Method ● Fill the burette with FA 2. ● Pipette 25.0 cm3 of FA 1 into a conical flask. ● Use the 25 cm3 measuring cylinder to transfer 25 cm3 of FA 3 into the same conical flask. ● Carry out a rough titration and record your burette readings in the space below.  The rough titre is … cm3. ● Carry out as many accurate titrations as you think necessary to obtain consistent results. ● Make sure any recorded results show the accuracy of your practical work. ● Record in a suitable form below all your burette readings and the volume of FA 2 added in each accurate titration. Keep FA 1 for use in Question 3.  [7] I II III IV V VI VII

3 9701/31/M/J/21 © UCLES 2021 [Turn over (b) From your accurate titration results, obtain a suitable value to be used in your calculations. Show clearly how you obtained this value.  25.0 cm3 of FA 1 required … cm3 of FA 2. [1] (c) Calculations (i) Give your answers to (c)(ii), (c)(iii) and (c)(iv) to an appropriate number of significant figures. [1] (ii) Calculate the number of moles of potassium manganate(VII) present in the volume of FA 2 calculated in (b).  moles of KMnO4 = … mol [1] (iii) Calculate the number of moles of iron(II) sulfate present in 1.00 dm3 of FA 1.  moles of FeSO4 = … mol [1] (iv) Calculate the mass of iron(II) sulfate present in 1.00 dm3 of FA 1.  mass of FeSO4 = … g [1] (v) Calculate the value of x in FeSO4•xH2O.  x = … [2]

4 9701/31/M/J/21 © UCLES 2021 (d) Iron(II) sulfate in solution is readily oxidised by air to form iron(III) sulfate. State the effect, on the value of x calculated in (c)(v), if some of your sample of FA 1 had oxidised before you carried out the titration. Explain your answer. … … … … [2]  [Total: 16]

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6 9701/31/M/J/21 © UCLES 2021 2 In Question 1 you used a titration method to determine the value of x in a hydrated salt. In Question 2 you will use a gravimetric method. In this method a sample of solid is heated to remove the water of crystallisation. You will carry out this method on a different hydrated compound, FA 4, with formula MZ•yH2O. In FA 4 the value of y is an integer. MZ•yH2O(s) → MZ(s) + yH2O(g) FA 4 is a hydrated compound, MZ•yH2O. (a) Method ● Weigh the crucible with its lid. Record the mass. ● Place between 2.40 g and 2.60 g of FA 4 in the crucible and record its appearance below. ● Weigh the crucible, its lid and contents and record the mass. ● Without the lid, place the crucible on the pipe-clay triangle and heat gently for approximately one minute and record your observations. ● Then heat more strongly for approximately four minutes. ● Place the lid on the crucible and leave it to cool. You may wish to start Question 3 while you are waiting for the crucible to cool. ● Weigh the crucible, its lid and contents and record the mass. ● Calculate and record the mass of FA 4, the mass of residue after heating and the mass of water lost. Keep FA 4 for use in Question 3. Results appearance of FA 4 … observations during heating for the first minute … …  [4] I II III IV

7 9701/31/M/J/21 © UCLES 2021 [Turn over (b) Calculations (i) Calculate the number of moles of water lost when your sample of MZ•yH2O was heated.  moles of water = … mol The relative formula mass of the anhydrous compound MZ is 120.4. Calculate the number of moles of MZ present in the residue.  moles of MZ = … mol  [1] (ii) Use your answers from (b)(i) to calculate the value of y in FA 4, MZ•yH2O. Show your working.  y = … [1] (iii) State an assumption you made when calculating the value of y in the hydrated compound. … [1] (c) A student suggested that the experiment would be more accurate if the crucible had been heated with the lid on for the first minute. State and explain whether you agree with the student. … … [1]  [Total: 8]

8 9701/31/M/J/21 © UCLES 2021 Qualitative analysis Where reagents are selected for use in a test, the name or correct formula of the element or compound must be given. At each stage of any test you are to record details of the following: ● colour changes seen ● the formation of any precipitate and its solubility in an excess of the reagent added ● the formation of any gas and its identification by a suitable test. You should indicate clearly at what stage in a test a change occurs. If any solution is warmed, a boiling tube must be used. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests for ions present should be attempted. 3 (a) Aqueous ammonium thiocyanate reacts with aqueous iron(III) ions to form an orange or red coloured compound. Iron(II) ions do not react in this way. The darker the orange or red colour, the more iron(III) ions are present in the solution. (i) For each test use a 1 cm depth of FA 1 in a test‑tube. Record all your observations. test observations Test 1 Add a few drops of aqueous ammonium thiocyanate. Test 2 Add a few drops of aqueous sodium hydroxide and leave for at least two minutes, then add dilute sulfuric acid dropwise until there is no further change, then add a few drops of aqueous ammonium thiocyanate.  [3]

9 9701/31/M/J/21 © UCLES 2021 [Turn over (ii) Suggest a reason for any difference in observation when you added aqueous ammonium thiocyanate in Test 2 compared with Test 1. Your answer should refer to the type of reaction that occurred in Test 2. … … … [2] (iii) The charge on the thiocyanate ion, SCN–, is –1. Determine the formula of ammonium thiocyanate. … [1] (iv) A solution containing Fe2+ reacts with aqueous ammonia to form a green precipitate. Write the ionic equation for this reaction. Include state symbols. … [2]

10 9701/31/M/J/21 © UCLES 2021 (b) FA 4 contains one cation and one anion, both of which are listed in the Qualitative Analysis Notes. The anion in FA 4 contains sulfur. (i) Carry out appropriate tests to allow you to identify the cation and anion in FA 4. Record each test and your observations in a suitable form below.  [7] (ii) Give the formula of the ions present in FA 4. cation … anion …  [1]  [Total: 16]

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14 9701/31/M/J/21 © UCLES 2021 Qualitative analysis notes 1 Reactions of aqueous cations ion 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 heating – barium, Ba2+(aq) faint white ppt. is nearly always observed unless reagents are pure no ppt. calcium, Ca2+(aq) white ppt. with high [Ca2+(aq)] no ppt. chromium(III), Cr3+(aq) grey-green ppt. soluble in excess 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

15 9701/31/M/J/21 © UCLES 2021 2 Reactions of anions ion 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 ppt. with Ag+(aq) (partially soluble in NH3(aq)) iodide, I –(aq) gives 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 sulfate, SO4 2–(aq) gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids) sulfite, SO3 2–(aq) gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids) 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 (ppt. dissolves with excess CO2) chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint

16 9701/31/M/J/21 © UCLES 2021 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 – 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 144.4 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 –

This document consists of 10 printed pages. © UCLES 2021 [Turn over Cambridge International AS & A Level CHEMISTRY 9701/31 Paper 3 (Advanced Practical Skills 1) May/June 2021 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 2021 series for most Cambridge IGCSE™, Cambridge International A and AS Level components and some Cambridge O Level components.

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 2 of 10 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.

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 3 of 10 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.

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 4 of 10 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. When awarding accuracy (Q) marks in Question 1, the following information must be recorded on a blank part of Supervisor’s script/report or on the form provided or on a sheet of paper stapled to the Supervisor’s script. • candidate number • candidate titre • difference from Supervisor • mark awarded • any spread penalty The Supervisor’s results are treated as suspect in either experiment if more than 50% of the candidates score zero Q marks. In this case, or if no supervisor’s results are supplied, each Examiner should consider using a mean value derived from ‘consistent’ candidates’ results, but this must be discussed with your team leader. If a CDM is employed in Question 1 then the better accuracy mark stands. Rounding errors and transcription errors are penalised only once in the paper.

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 5 of 10 Question Answer Marks 1(a) I The following data must be shown • burette readings and titre for rough titration • 2 × 2 ‘box’ showing both accurate burette readings ‘Correct’ headings and units are not required for this mark 1 II Headings and units correct for accurate titration table and headings match readings. • initial/start and (burette) reading / volume + unit (allow vol but not V) • final/end and (burette) reading / volume + unit (allow value for reading) • titre or volume/FA 2 and used/added (not ‘difference’ or ‘total’ or ‘amount’) + unit Units: (cm3) or / cm3 or in cm3 or cm3 by every entry 1 III All accurate burette readings to 0.05 cm3 Do not award this mark if: 50(.00) is used as an initial burette reading; More than one final burette reading is 50(.00); Any burette reading is greater than 50(.00). 1 IV The final accurate titre recorded is within 0.10 cm3 of any other accurate titre. Do not award the mark if any ‘accurate’ burette readings (apart from initial 0) are given to zero dp. 1 For assessment of accuracy (Q) marks, the Examiner should round any 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. Calculate the difference (δ) between the candidate’s titre and the supervisor’s titre. Award the accuracy (Q) marks as shown below. 1 Award V if δ ⩽ 0.50 cm3 1 Award VI if δ ⩽ 0.30 cm3 1 Award VII if δ ⩽ 0.20 cm3

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 6 of 10 Question Answer Marks 1(b) Candidate must average two (or more) titres that are all within 0.20 cm3. Working must be shown or ticks must be put next to the two (or more) accurate titres selected. 1 1(c)(i) Answers for (c)(ii), (c)(iii), (c)(iv) to 3–4 sf 1 1(c)(ii) Correctly calculates n(MnO4−) = 0.02 × (b) / 1000 1 1(c)(iii) Correctly uses n(FeSO4) in 25 cm3 = (c)(ii) × 5 × 40 1 1(c)(iv) Correctly uses mass(FeSO4) in 1 dm3 = (c)(iii) × 151.9 1 1(c)(v) Correctly uses n(H2O) = [26.52 – (c)(iv)] / 18 1 ratio n(H2O) : n((FeSO4) AND x given as integer OR M1: Mr hydrated salt = 26.52 / (c)(iii) M2: (26.52 / (c)(iii) – 151.9) / 18 and answer as integer 1 1(d) (as) mole / amount / volume MnO4− smaller or (as) mass / moles / amount Fe2+ smaller 1 mass/moles/amount water larger so (mole) ratio larger so x increases Allow difference in titre/moles of MnO4− / Fe2+ will be too small to change the (integer) value of x for 1 mark. Allow for 1 mark: less MnO4− / Fe2+ and x increases 1

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 7 of 10 Question Answer Marks 2(a) I Appearance FA 4: white / colourless and crystals /solid AND obs during heating: swelling / steam / (some) solid melts / dissolves / white powder forms around the edges Allow evaporation of water Allow bubbling / bubbles of water Ignore fizzing / effervescence 1 II Unambiguous headings and units in list / table of data: • (Mass of) crucible and lid (not ‘weight’ in any reading) • (Mass of) crucible, lid and FA 4 (or ‘contents before heating’) • (Mass of) crucible, lid and residue / contents after heating • (Mass of) FA 4 (used) • (Mass of) residue • (Mass of) water (lost) Ignore mention of 1st heating if reheated Do not allow ‘mass of FA 4 after heating’ in third weighing. Use of lid must be consistent. Unit must be given correctly in each case. 1 III Three weighings recorded and all listed subtractions (minimum one) correct • All weighings to the same number of dp • Mass of FA 4 used between 2.40 and 2.60 g If 4 weighings shown then all must be to the same number of dp 1 IV Accuracy mark Award if ratio between 1.80–2.10 1 2(b)(i) Correctly calculates n(H2O) = mass loss in (a) / 18 and answer to 2 or more sf AND n(MZ) = mass of residue in (a) / 120.4 and answer to 2 or more sf If masses are not shown in (a) then values used must be correct 1

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 8 of 10 Question Answer Marks 2(b)(ii) Shows use of ratio n(MZ) : n(H2O) AND y is an integer Other correct methods are available. 1 2(b)(iii) One of the following • All water (of crystallisation) was lost / dehydration was complete • No MZ decomposed on heating 1 2(c) One of the following • student incorrect and because there was no spitting (and therefore lid not required) • student correct and to catch any spitting (check observations for spitting or swelling) • student incorrect and because putting the lid on makes no difference to water (vapour) escaping 1

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 9 of 10 Question Answer Marks 3(a)(i) Test 1 no change / (pale) orange / (pale) red / (pale) pink solution Allow solution becomes colourless / paler 1 Test 2 + NaOH green / dirty green / pale green / dark green ppt * ppt turns brown (at surface) * + H2SO4 ppt dissolves or yellow / yellow-brown / orange-brown solution formed * + SCN− (solution) turns dark(er) orange / blood-red / red / dark(er) red / deep red / red-brown * colour must be more intense than in Test 1 2 asterisks = 1 mark (round down) 2 3(a)(ii) Fe3+ is formed (in Test 2) 1 oxidation of Fe2+ / redox 1 3(a)(iii) NH4SCN 1 3(a)(iv) Fe2+(aq) + 2OH−(aq) → Fe(OH)2(s) correct product formula 1 balancing and state symbols 1

9701/31 Cambridge International AS & A Level – Mark Scheme PUBLISHED May/June 2021 © UCLES 2021 Page 10 of 10 Question Answer Marks 3(b)(i) prepare solution of FA 4 1 prepare a suitable table(s) minimum 2 tests and columns/ rows for tests and for observations 1 2 asterisks = 1 mark (round down) +NaOH * white ppt * insoluble in excess * + NH3 * white ppt* insoluble in excess * BaCl2/Ba(NO3)2* HCl / HNO3 * white ppt * insoluble in excess suitable named acid * OR dilute acid * + KMnO4 * no change / no reaction / solution remains purple ** Ignore additional reagents 5 3(b)(ii) cation: Mg2+ and anion: SO42− 1