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Chemistry 9701/31 May/June 2022: question paper and mark scheme

Cambridge AS & A Level Chemistry (9701), Paper 3 Advanced Practical Skills 1, May/June 2022. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.

9701_s22_qp_319701_s22_ms_319701/31/M/J/22

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Paper
Paper 3 Advanced Practical Skills 1
Total marks
40
Questions
3
Code on the paper
9701/31/M/J/22
9701_s22_ms_31.pdf

9701/31 mark scheme, question by question

Each question as it's printed, and the mark scheme's points for it, as text. Diagrams, tables and graphs are in the PDFs above.

Question 114 marks

Question

In this experiment you will identify a straight-chain carboxylic acid by titrating an aqueous solution of this acid with aqueous sodium hydroxide. 1 mole of the carboxylic acid reacts with 1 mole of sodium hydroxide. The carboxylic acid contains C, H and O atoms only and has no C=C bonds. FA 1 is an aqueous solution of the carboxylic acid, containing 10.50 g dm–3. FA 2 is 0.110 mol dm–3 sodium hydroxide, NaOH. FA 3 is thymolphthalein indicator. (a) Method ● Fill the burette with FA 2. ● ipette 25.0 cm3 of FA 1 into a conical flask. P ● Add approximately 8 drops of FA 3. ● Perform 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 precision 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. I II III IV V VI VII [7] (b) From your accurate titration results, calculate a suitable mean value to use in your calculations. Show clearly how you obtain the mean value. 25.0 cm3 of FA 1 required …… cm3 of FA 2. [1] (c) Calculations (i) Calculate the amount, in mol, of sodium hydroxide present in the volume of FA 2 calculated in (b). amount of NaOH = …… mol [1] (ii) Use your answer to (c)(i) and the information on page 2 to calculate the relative formula mass of the carboxylic acid in FA 1. Mr of carboxylic acid = …… [1] (iii) Identify the carboxylic acid in FA 1. Draw its skeletal formula. skeletal formula name of acid …… [2] (d) A student carries out a similar titration to the titration you carried out in (a). The only difference is that a solution of aminoethanoic acid, NH2CH2CO2H, containing 10.50 g dm–3 is used instead of the acid in FA 1. (i) Construct an equation for the reaction taking place in the student’s titration. Include state symbols. . …… [1] (ii) State whether the student’s titre will be larger or smaller than your titre. Explain your answer. The student’s titre will be …… than mine. explanation …… . …… . …… [1] [Total: 14]

Mark scheme

1(a) I All the following data are recorded: 1 two burette readings and titre for the rough titration initial and final burette readings for two (or more) accurate titrations II Appropriate headings and units in the accurate titration table and titre values recorded for accurate titrations 1 initial / start and (burette) reading / volume final / end and (burette) reading / volume titre or volume used / added / or FA 2 added unit: / cm3 or (cm3) or in cm3 (for each heading) or cm3 unit given for each volume recorded III All accurate burette readings are recorded to the nearest 0.05 cm3 1 IV The final accurate titre recorded is within 0.10 cm3 of any other accurate titre 1 For assessment of accuracy marks, round all burette readings to the nearest 0.05 cm3. Check and correct subtractions where necessary. 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 Supervisor’s [corrected] mean titre in a ring on each candidate script. Calculate the difference (δ) between the candidate’s mean titre and the Supervisor’s. Write the value of δ on each script. Award the accuracy marks as shown below. Award V if δ ⩽ 0.50 (cm3) 3 Award VI if δ ⩽ 0.30 Award VII if δ ⩽ 0.20 1(b) Candidate must average two (or more) titres that are within a total spread of not more than 0.20 cm3 1 AND working / explanation must be shown or ticks must be put next to the two (or more) accurate titres selected AND mean quoted to 2 decimal places 1(c)(i) Correctly calculates 1 moles of NaOH used = 0.110 × (b) / 1000 AND answer to 3 or 4 sig fig 1(c)(ii) Correctly uses 1 (c)(i) to calculate Mr = 10.5 / (c)(i) × 40 1(c)(iii) M1 Identity of carboxylic acid [must be consistent with the Mr in (c)(ii)] 2 M2 Skeletal formula (must correspond to candidate’s name of acid) 1(d)(i) Correct equation with state symbols 1 NH2CH2COOH(aq) + NaOH(aq) → NH2CH2COONa(aq) + H2O(l) 1(d)(ii) Student’s titre would be larger 1 AND Mr of amino acid is 75 / is lower than Mr of FA 1 so more moles of amino acid are present ORA

Question 211 marks

Question

In this experiment you will identify a magnesium compound by thermal decomposition. When heated this compound decomposes to give magnesium oxide. FA 4 is the magnesium compound. (a) Method ● Weigh the empty crucible with its lid. Record the mass. ● Transfer all the FA 4 from the container into the crucible. ● Weigh the crucible, lid and FA 4. Record the mass. ● Calculate the mass of FA 4. Record the mass. ● Place the crucible and contents on a pipe-clay triangle. ● Heat the crucible gently, without the lid, for approximately 2 minutes. ● Heat strongly for a further 4 minutes. ● Place the lid on the crucible and leave it to cool for at least 5 minutes. During the cooling period, you may wish to begin work on Question 3. ● When the crucible is cool, weigh the crucible with its lid and contents. Record the mass. ● Heat strongly, without the lid, for a further 2 minutes. ● Replace the lid and leave the crucible to cool for at least 5 minutes. ● When the crucible has cooled, reweigh the crucible with its lid and contents. Record the mass. ● Calculate the mass of residue obtained. Record the mass. Results I II III IV V [5] (b) Calculations (i) Calculate the amount, in mol, of magnesium oxide produced in your experiment. amount of MgO = …… mol [1] (ii) 1 mole of FA 4 decomposes on heating to produce 1 mole of MgO and 1 mole of gas X. Calculate the relative formula mass, Mr , of X. Mr of X = …… [1] (iii) X contains one or more oxygen atoms. Suggest the identity of X. X is …… . [1] (iv) Deduce the name of FA 4. FA 4 is …… . [1] (c) A student suggests that this experiment will be more accurate if FA 4 is heated throughout the experiment with a lid on the crucible. State whether the student is correct. Explain your answer. . …… . …… . …… [1] (d) State the uncertainty in a single reading of your balance. uncertainty = ± …… g Calculate the maximum percentage error in the mass of residue that you obtained. Show your working. maximum percentage error = ……% [1] [Total: 11] 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. Rinse and reuse test-tubes and boiling tubes where possible. No additional tests should be attempted.

Mark scheme

2(a) I Unambiguous headings and units for four weighings: 1 (mass of) crucible, lid (empty) (mass of) crucible, lid and FA 4 (or ‘contents before heating’) (mass of) crucible, lid and MgO / residue after first heating (mass of) crucible, lid and MgO / residue after second heating II Readings are appropriately recorded: 1 all weighings recorded to same decimal places (two or more) mass of FA 4 is within range 0.80 g–1.80 g (from weighings) fourth weighing within +0.02 and –0.05 g of third weighing III Correct subtractions to give masses of FA 4 and MgO / residue 1 IV and V: Accuracy marks 2 Calculate supervisor’s mass ratio (to 2 d.p.) = mass FA 4 / mass of residue Calculate the candidate’s mass ratio (to 2 d.p.) = mass FA 4 / mass of residue Calculate 20% of this ratio and calculate ratio ± this ratio Award IV if δ is within the range 0.00–0.25 Award V if δ is within the range 0.00–0.10 2(b)(i) Correctly calculates 1 moles of MgO = mass of residue / 40.3 AND answer to 2–4 sig fig 2(b)(ii) Correctly uses 1 (b)(i) to calculate Mr of X = mass lost / moles of MgO OR Mr of X = (mass FA 4 / moles of MgO) – 40.3 AND answer to 2–4 sf 2(b)(iii) X is water / steam / H2O / CO2 1 2(b)(iv) FA 4 is magnesium hydroxide 1 2(c) Student is not correct because there is no spitting / frothing during heating 1 OR student is correct because there was spitting / frothing during heating 2(d) 2 d.p. balance uncertainty = 0.01 g or 0.005 g 1 3 d.p. balance uncertainty = 0.001 g or 0.0005 g Correct expression for % error = (2 × balance uncertainty / mass of residue) × 100 FA 5 is NaNO3; FA 6 is Al 2(SO4)3; FA 7 is I2 + KI

Question 315 marks

Question

(a) FA 5 is an ionic solid containing two ions. It contains one or more ions that contain nitrogen. (i) Carry out suitable tests to identify the anion. Reserve a small amount of FA 5 for use in (a)(ii). Record the tests you carry out and the observations you make, in a table, in the space below. You must use a boiling tube if any liquid is heated. anion in FA 5 = …… [4] (ii) Heat a small spatula measure of FA 5 in a hard-glass test-tube. When no further change occurs, allow the tube and its contents to cool completely. Record all the observations you make and any subsequent conclusions. . …… . …… . …… . …… [2] (b) FA 6 is a solution of a compound containing one cation and one anion, both of which are in the Qualitative analysis notes. FA 7 is an aqueous mixture of two substances. FA 7 contains one potassium-containing compound and one other substance. All substances are listed in the Qualitative analysis notes. (i) Carry out the following tests. Complete the table below. Use a 1 cm depth of FA 6 or FA 7 in a test-tube for each test. Table 3.1 observations test FA 6 FA 7 Test 1 Add aqueous sodium hydroxide. Test 2 Add aqueous barium chloride or aqueous barium nitrate, then add dilute hydrochloric acid. Test 3 Add a few drops of aqueous starch, then add aqueous sodium thiosulfate. Test 4 Add a few drops of aqueous silver nitrate, then add a few drops of aqueous sodium hydroxide. Test 5 Add aqueous ammonia. [5] (ii) Give the formulae of the substances in FA 6 and FA 7. FA 6 is …… . (iii) Give the ionic equation for one of the reactions taking place in Test 1. Include state symbols. . …… [1] [Total: 15] 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 no ppt. [Ba2+(aq)] is very low calcium, Ca2+(aq) white ppt. unless [Ca2+(aq)] is very no ppt. low chromium(III), Cr3+(aq) grey-green ppt. soluble in excess grey-green ppt. insoluble in excess giving dark green solution 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 green ppt. turning brown on contact with air contact with air insoluble in excess 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 off-white ppt. rapidly turning brown on contact with air on contact with air insoluble in excess insoluble in excess zinc, Zn2+(aq) white ppt. soluble in excess white ppt. soluble in excess 2 Reactions of anions anion reaction carbonate, CO32– 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, SO42–(aq) gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids); gives white ppt. with high [Ca2+(aq)] sulfite, SO32–(aq) gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids); decolourises acidified aqueous KMnO4 thiosulfate, S2O32–(aq) gives off-white / pale yellow ppt. slowly with H+ 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 = 6.022 × 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 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 12 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 138.9 140.1 140.9 144.4 – 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

3(a)(i) M1: ‘table’ (2 × 2 min) with headings: ‘test / experiment / reagents’ and ‘observations’ 4 AND two (or more) reagents listed in the space M2: (eliminating ammonium ion) heat FA 5 with (aqueous) NaOH AND no effervescence / (damp red) litmus stays red M3: (identifying NO2– / NO3–) add Al to warm NaOH and FA 5 AND fizz / gas / NH3 turns (damp red) litmus blue M4: (eliminating NO2−) anion is NO3− / nitrate / nitrate(V) AND Either add (a few drops of) (acidified) KMnO4 / potassium manganate(VII) AND no change / no reaction / (solution) remains purple Or add (dilute) named mineral acid to (solid or aqueous) FA 5 AND no brown fumes / no blue solution / no reaction / no change produced 3(a)(ii) solid melts / solid dissolves / liquid forms 2 fizzing / bubbling / effervescence (gas) re-lights glowing splint / spill oxygen produced (on cooling), (pale) yellow solid formed or residue is yellow 3 or more bullets = 2 marks 2 bullets = 1 mark 3(b)(i) 5 test FA 6 FA 7 Test 1 White ppt / solid (formed) * Decolourises / turns (pale) yellow * NaOH Soluble in excess * (ppt is CON) Test 2 Ba2+ White ppt No change / no reaction + HCl AND ppt insoluble / remains / no AND no change / no reaction * change / no reaction * Test 3 starch Dark blue / blue-black / black (colour formed) (ignore state) + thio AND colourless solution (forms) ALLOW turns colourless / decolourises * Test 4 Ag+ No change / no reaction / no ppt Yellow / brown ppt (forms) * + NaOH AND ppt (forms) (ignore colour) * Pale yellow ppt ALLOW ppt turns paler yellow * IGNORE use of excess NaOH Test 5 + NH3 White ppt AND ppt is insoluble in excess (NH3) * 2 * = 1 mark (round down) 3(b)(ii) FA 6 = Al 2(SO4)3 [1] 3 FA 7 = I2 [1] AND KI [1] 3(b)(iii) Al 3+(aq) + 3OH–(aq) → Al (OH)3(s) 1 OR Al (OH)3(s) + OH−(aq) → [Al (OH)4]−(aq) OR I2(aq) + 6OH–(aq) → I–(aq) + IO3–(aq) + 3H2O(l)

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On this page, free: the mark scheme for AS & A Level Chemistry 9701/31, May/June 2022 (9701_s22_ms_31), and the question paper (9701_s22_qp_31), to read or download, with each question's marking points written out underneath.

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Chemistry 9701/31 for May/June 2022 is out of 40 marks, across 3 questions.

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