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Chemistry 9701/35 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_359701_s22_ms_359701/35/M/J/22

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Paper
Paper 3 Advanced Practical Skills 1
Total marks
40
Questions
3
Code on the paper
9701/35/M/J/22
9701_s22_ms_35.pdf

9701/35 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 110 marks

Question

Basic copper(II) carbonate contains both copper(II) carbonate, CuCO3, and copper(II) hydroxide, Cu(OH)2. The ratio of these two components can be different in samples from different sources. This means that the formula of basic copper(II) carbonate can be written as CuCO3•xCu(OH)2. Both the carbonate and the hydroxide react with acids. CuCO3(s) + 2HCl (aq) → CuCl 2(aq) + CO2(g) + H2O(l) Cu(OH)2(s) + 2HCl (aq) → CuCl 2(aq) + 2H2O(l) You will determine the value of x in a sample of basic copper(II) carbonate by reacting it with excess acid and measuring the mass of carbon dioxide given off. FA 1 is basic copper(II) carbonate, CuCO3•xCu(OH)2. FA 2 is 2.0 mol dm–3 hydrochloric acid, HCl. (a) Method ● Use the 25 cm3 measuring cylinder to transfer 25.0 cm3 of FA 2 into a conical flask. ● Weigh the flask with the acid. Record the mass. ● Weigh the container with FA 1. Record the mass. ● Carefully tip all of FA 1 into the acid in the conical flask. Swirl the contents of the flask and leave the flask to stand. ● Weigh the container with any residual FA 1. Record the mass. ● Calculate and record the mass of FA 1 added to the flask. ● Calculate and record the theoretical initial mass of flask + acid + FA 1. ● Swirl the flask occasionally. Weigh the flask and contents after approximately 5 minutes. Record the mass. During this step you may wish to continue with Question 2 or Question 3. ● Calculate and record the mass of carbon dioxide given off during the experiment. Results I II III IV [4] (b) Calculations (i) Calculate the amount, in mol, of carbon dioxide given off in the reaction. amount of CO2 = …… mol [1] (ii) Calculate the amount, in mol, of copper(II) carbonate in the sample of FA 1 that you added to the flask. amount of CuCO3 = …… mol Hence calculate the mass of copper(II) carbonate in the sample of FA 1 that you added to the flask. mass of CuCO3 = …… g [1] (iii) Calculate the mass of copper(II) hydroxide in the sample of FA 1 that you added to the flask. mass of Cu(OH)2 = …… g [1] (iv) Calculate the amount, in mol, of copper(II) hydroxide in the sample of FA 1 that you added to the flask. amount of Cu(OH)2 = …… mol Hence calculate the value of x in the formula of basic copper(II) carbonate, CuCO3•xCu(OH)2. x = …… [1] (c) In this determination you assume that hydrochloric acid is in excess. Show, by calculation, that this assumption is correct. [2] [Total: 10]

Mark scheme

1(a) l Unambiguous headings and correct units 4 Units: / g, (g), in gram(me)s with each entry or in heading. (mass of) flask + acid (mass of) container + FA 1 (mass of) container (+ residue) (final / constant mass of) flask + contents (mass of) FA 1 (added) theoretical (initial / total) mass (mass of) CO2 (evolved) ll Four weighings recorded to the same number of decimal places and to at least 2 dp lll Three masses correctly calculated mass FA 1 IV Award if ratio (to 2 dp) is within 20% of supervisor’s value mass CO2 1(b)(i) Correctly calculates moles of CO2 = mass loss / 44 1 AND answer to 2–4 significant figures 1(b)(ii) Deduces moles CuCO3 = (b)(i) 1 AND correctly uses mass CuCO3 = moles × 123.5 AND answer to 2–4 significant figures 1(b)(iii) Mass Cu(OH)2 = FA 1 – (ii) 1 1(b)(iv) Moles Cu(OH)2 = (iii) / 97.5 1 AND ratio moles Cu(OH)2 / moles CuCO3 1(c) M1 moles HCl = 2 × 25 / 1000 = 0.05 2 AND moles reacting in FA 1 = moles CuCO3 + moles Cu(OH)2 M2 0.05 > 2 × (moles CuCO3 + moles Cu(OH)2) OR M1 moles of HCl required = 2 × (moles CuCO3 + moles Cu(OH)2) M2 vol of HCl required = moles required × 1000 / 2 AND volume required < 25 cm3

Question 217 marks

Question

In Question 1 you found the value of x in the formula of basic copper(II) carbonate, CuCO3•xCu(OH)2. You will now use another method to find the value of x. Copper(II) ions oxidise iodide ions to produce iodine. 2Cu2+(aq) + 4I–(aq) → I2(aq) + 2CuI(s) The amount of iodine produced can be found by titration with aqueous thiosulfate ions, S2O32–. 2S2O32–(aq) + I2(aq) → S4O62–(aq) + 2I–(aq) FA 3 contains Cu2+(aq). It was made by reacting 10.40 g of CuCO3•xCu(OH)2 with excess dilute sulfuric acid and making the solution up to 1.00 dm3 with distilled water. FA 4 is 0.100 mol dm–3 sodium thiosulfate, Na2S2O3. FA 5 is aqueous potassium iodide, KI. FA 6 is starch indicator. (a) Method ● Fill the burette with FA 4. ● ipette 25.0 cm3 of FA 3 into a conical flask. P ● Rinse the 25 cm3 measuring cylinder with approximately 5 cm3 of FA 5. Discard the solution used for rinsing. ● Use the 25 cm3 measuring cylinder to add 15 cm3 of FA 5, an excess of KI, to the conical flask. The solution will turn brown because iodine is formed. ● Add FA 4 from the burette until the mixture changes to pale brown. ● Add approximately 10 drops of FA 6. The mixture will turn blue-black. ● Continue adding FA 4 from the burette until the blue-black colour disappears to leave an off-white solid. This is the end-point of the titration. ● 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 certain 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 4 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 be used in your calculations. Show clearly how you have obtained the mean value. 25.0 cm3 of FA 3 required …… cm3 of FA 4. [1] (c) Calculations (i) Give your answers to (c)(ii), (c)(iii) and (c)(iv) to the appropriate number of significant figures. [1] (ii) Calculate the amount, in mol, of thiosulfate ions present in the volume of FA 4 you have calculated in (b). amount of S2O32– = …… mol [1] (iii) Use your answer to (c)(ii), and the equations for the reactions involved, to calculate the amount, in mol, of copper(II) ions present in 25.0 cm3 of FA 3. amount of Cu2+ in 25.0 cm3 = …… mol Hence deduce the amount, in mol, of copper(II) ions present in 1.00 dm3 of FA 3. amount of Cu2+ in 1.00 dm3 = …… mol [1] (iv) Use your answer to (c)(iii) to calculate the mass of copper(II) ions in 1.00 dm3 of FA 3. mass of Cu2+ in 1.00 dm3 = …… g [1] (v) The formula of basic copper(II) carbonate is CuCO3•xCu(OH)2. Write an expression, including x, for the mass of Cu2+ ions in one mole of CuCO3•xCu(OH)2. mass of Cu2+ ions in one mole of CuCO3•xCu(OH)2 = …… g [1] (vi) The formula of basic copper(II) carbonate is CuCO3•xCu(OH)2. Write an expression, including x, for the mass of one mole of CuCO3•xCu(OH)2. mass of one mole of CuCO3•xCu(OH)2 = …… g [1] (vii) The expression below links the masses of copper(II) ions in FA 3 and in one mole. mass of Cu2+ present in sample of FA 3 mass of Cu2+ in one mole of CuCO3•xCu(OH)2 = mass of CuCO3•xCu(OH)2 used mass of one mole of CuCO3•xCu(OH)2 Using this expression, show how you could determine the value of x in the formula of basic copper(II) carbonate, CuCO3•xCu(OH)2. [3] [Total: 17] 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 Initial and final readings 7 AND titre recorded for rough titre and accurate titre details tabulated ll Headings and units correct for accurate titrations . initial / final (burette) reading / volume or reading / volume at start / finish titre or volume / FA 4 added / used Units:(cm3) or / cm3 or in cm3 or cm3 by every entry IIl All accurate burette readings are recorded to the nearest 0.05 cm3 IV Final (uncorrected) titre is within 0.10 cm3 of any other accurate titre For assessment of accuracy the examiner should round any burette readings to the nearest 0.05 cm3, check subtractions and then select the ‘best titres’ using the hierarchy: two (or more) accurate identical titres, 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 corrected titre to the nearest 0.01 cm3. Award V if δ ⩽ 0.80 cm3 Award VI if δ⩽ 0.50 cm3 Award VII if δ⩽ 0.30 cm3 If supervisor’s titre is ⩽ 10.00 cm3 then tolerances are 0.15, 0.25 and 0.40 cm3. If supervisor’s titre is ⩽ 5.00 cm3 then tolerances are 0.10, 0.15 and 0.25 cm3. 2(b) Candidate must average two (or more) accurate titres where the total spread is ≤ 0.20 cm3. 1 Working must be shown or ticks must be put next to the two (or more) accurate titres selected. 2(c)(i) All quoted answers to (c)(ii) to (c)(iv) to 3–4 significant figures (minimum 3 answers attempted). 1 2(c)(ii) Correctly calculates 1 moles in (b) × 0.1 / 1000 2(c)(iii) Correctly uses 1 moles Cu2+ in 25 cm3 = (c)(ii) AND moles Cu2+ in 1.0 dm3 = moles Cu2+ in 25 cm3 × 40 2(c)(iv) Correctly uses (c)(iii) × 63.5 1 2(c)(v) Correct expression 1 mass of Cu2+ = 63.5 (1 + x) 2(c)(vi) mass of 1 mol = 123.5 + 97.5x 1 2(c)(vii) (c)(iv) 3 M1 LHS 10.4 g 63.5 (1 + x ) M2 RHS 123.5 + 97.5x M3 shows cross multiplication and simplification in attempt to calculate x FA 7 is CuCO3•Cu(OH)2(s); FA 8 is CuSO4(aq); M is Mg(s); FA 9 is Na2CO3(aq); FA 10 is KI(aq)

Question 313 marks

Question

FA 7 is a sample of basic copper(II) carbonate. (a) Place a small spatula measure of FA 7 into a hard-glass test-tube and heat the tube, gently at first and then more strongly. Record all your observations. . …… . …… . …… . …… [2] (b) FA 8 is an aqueous solution containing Cu2+ ions. (i) Carry out the following tests using a 1 cm depth of FA 8 in a test-tube for each test. Record your observations. Table 3.1 test observations Test 1 Add a 1 cm depth of aqueous EDTA. Test 2 Add concentrated hydrochloric acid (CARE, corrosive) dropwise until no further change is seen. Test 3 Add a small spatula measure of metal M. Leave the test-tube to stand. [2] (ii) Suggest a possible ionic equation for the reaction between M and FA 8 in Test 3. Include state symbols. . …… [1] (c) Carry out tests to identify M. Use only a small spatula measure of M. Do not use concentrated hydrochloric acid in your tests. (i) Record the tests you carry out and the observations you make, in a table, in the space below. [3] (ii) From your observations in (c)(i), identify M. M is …… . [1] (d) FA 9 and FA 10 are sodium compounds that contain either a halide or a carbonate. Carry out tests to confirm the identity of FA 9 and FA 10. Record the tests you carry out, the observations you make and your conclusions in a table in the space below. [4] [Total: 13] 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) Any two from: 2 solid goes black / colour change green to black condensation / water on cool part tube / steam gas / CO2 given off turns limewater to white ppt 3(b)(i) 2 test observation + edta darker blue * + HCl green / yellow * +M solution goes pale * black solid / ppt * ignore any fizz 2 * = 1 mark 3(b)(ii) Cu2+(aq) + M(s) → Cu(s) + M2+(aq) 1 OR Cu2+(aq) + 2M(s) → Cu(s) + 2M+(aq) OR 3Cu2+(aq) + 2M(s) → 3Cu(s) + 2M3+(aq) 3(c)(i) M1 add named acid AND effervescence 3 M2 (to resulting solution) add NaOH AND NH3 M3 white ppt insoluble in excess for both alkalis 3(c)(ii) M is magnesium 1 3(d) M1 table with unambiguous headings (test/reagent and observations / results and conclusion) AND any 2 or more reagents 4 M2 selects suitable reagents AgNO3(aq) AND either named (dilute) acid or named solution that will form a ppt with carbonate but not with a halide e.g. named (aq) barium salt M3 result and conclusion for FA 9 fizz / effervescence / bubbling with acid / correct colour of ppt with suitable salt solution AND FA 9 is carbonate / CO32− M4 result and conclusion for FA 10 yellow ppt (ignore addition of (aq) ammonia) AND FA 10 is iodide / I−

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Chemistry 9701/35 for May/June 2022 is out of 40 marks, across 3 questions.

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