Chemistry 9701/31 October/November 2022: question paper and mark scheme

Question

Group 1 elements form salts with ethanedioic acid. These salts are ethanedioates and have the formula (COOM)2•2H2O, where M is the Group 1 metal. Ethanedioate ions react with manganate(VII) ions as shown. 5(COO–)2(aq) + 2MnO4–(aq) + 16H+(aq) → 10CO2(g) + 2Mn2+(aq) + 8H2O(l) You will determine which metal is present in (COOM)2•2H2O by titrating a solution of this salt with manganate(VII) ions. FA 1 is 10.14 g dm–3 aqueous hydrated ethanedioate of metal M, (COOM)2•2H2O. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1 mol dm–3 sulfuric acid, H2SO4. (a) Method ● Fill the burette with FA 2. ● ipette 25.0 cm3 of FA 1 into a conical flask. P ● Use the measuring cylinder to add approximately 20 cm3 of FA 3 into the conical flask. ● Place the conical flask on a tripod and gauze and heat carefully until the temperature of the solution is approximately 70 °C. ● Remove the flame. ● Carefully lift the hot conical flask and place it on the white tile under the burette. ● During titrations, add FA 2, slowly at first, until a permanent pale pink colour is formed. The pink colour on initial addition may take several seconds to disappear. ● If the reaction mixture turns brown, reheat it to about 70 °C. If the brown colour disappears, continue with the titration. If the brown colour remains, discard the contents of the flask and begin a new titration. ● Perform a rough titration with FA 2. 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 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 the appropriate number of significant figures. [1] (ii) Calculate the amount, in mol, of manganate(VII) ions, MnO4–, in the volume of FA 2 calculated in (b). amount of MnO4– = …… mol [1] (iii) Calculate the amount, in mol, of ethanedioate ions that reacted with the manganate(VII) ions in (c)(ii). amount of (COO–)2 = …… mol Hence calculate the concentration, in mol dm–3, of ethanedioate ions in FA 1. concentration of (COO–)2 = …… mol dm–3 [1] (iv) Calculate the relative formula mass, Mr, of the hydrated ethanedioate, (COOM)2•2H2O. Mr = …… [1] (v) Identify M. Show your working. M is …… . [2] (d) Explain why it is necessary to add FA 3 in each titration. . …… . …… [1] [Total: 15] Question 2 starts on the next page.

Question

Hydrated copper(II) sulfate, CuSO4•5H2O, can lose its water of crystallisation to form anhydrous copper(II) sulfate. The enthalpy change for the dehydration of hydrated copper(II) sulfate is shown in the equation. CuSO4•5H2O(s) → CuSO4(s) + 5H2O(l) You will carry out experiments to determine the enthalpy changes for the solution of hydrated and anhydrous copper(II) sulfate and then use Hess’s law to determine the enthalpy change of dehydration. FA 4 is hydrated copper(II) sulfate, CuSO4•5H2O. FA 5 is anhydrous copper(II) sulfate, CuSO4. Determination of the enthalpy change of solution of hydrated copper(II) sulfate. (a) Method ● Weigh the container with FA 4. Record the mass. ● Support the cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25.0 cm3 of distilled water into the cup. ● Measure and record the temperature of the water. ● Tip all the FA 4 into the water and stir until the solid dissolves. ● Measure and record the lowest temperature reached. ● Rinse and dry the cup ready for the next experiment. ● Weigh the container with any residual FA 4. Record the mass. ● Calculate and record the change in temperature. ● Calculate and record the mass of FA 4 used. Results [2] (b) Calculations (i) Calculate the energy change during this reaction. energy change = …… J [1] (ii) Calculate the amount, in mol, of hydrated copper(II) sulfate, FA 4, used in the experiment. Show your working. amount of CuSO4•5H2O = …… mol [1] (iii) Calculate the enthalpy change, in kJ mol–1, when 1.00 mol of hydrated copper(II) sulfate dissolves in water. This is the enthalpy of solution. enthalpy change of solution = …… …… kJ mol–1 [1] sign value Determination of the enthalpy change of solution of anhydrous copper(II) sulfate. (c) Method ● Weigh the container with FA 5. Record the mass. ● Support the cup in the 250 cm3 beaker. ● Use the measuring cylinder to transfer 25.0 cm3 of distilled water into the cup. ● Measure and record the temperature of the water. ● Tip all the FA 5 into the water and stir until the solid dissolves. ● Measure and record the highest temperature reached. ● Weigh the container with any residual FA 5. Record the mass. ● Calculate and record the change in temperature. ● Calculate and record the mass of FA 5 used. Results [1] (d) Calculations (i) Calculate the enthalpy change, in kJ mol–1, for the enthalpy change of solution of anhydrous copper(II) sulfate. enthalpy change = …… …… kJ mol–1 [2] sign value (ii) Use the enthalpy changes calculated in (b)(iii) and (d)(i) to calculate the enthalpy change of dehydration of hydrated copper(II) sulfate. CuSO4•5H2O(s) → CuSO4(s) + 5H2O(l) Show clearly how you obtained your answer. enthalpy change = …… …… kJ mol–1 [1] sign value (e) In the experiments in (a) and (c) you used the same method to determine the enthalpy change of solution of two solids. Tick the box to indicate which statement is correct. Ignore the effect of differences in mass used. The percentage error in (b)(iii) is less than the percentage error in (d)(i). The percentage errors in (b)(iii) and (d)(i) are equal. The percentage error in (b)(iii) is greater than the percentage error in (d)(i). Explain your choice. . …… . …… [1] [Total: 10] 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.

Question

(a) FA 6 is an aqueous solution that contains one cation and two anions. The three ions are listed in the Qualitative analysis notes. (i) Carry out the following tests on FA 6 and record your observations. test observations Test 1 To a 1 cm depth of FA 6 in a boiling tube add aqueous sodium hydroxide, then heat gently. Test 2 To a 1 cm depth of FA 6 in a boiling tube add a 1 cm depth of aqueous sodium hydroxide and a piece of aluminium foil. Heat gently. Test 3 To a 1 cm depth of FA 6 in a test‑tube add a few drops of hydrogen peroxide. [4] (ii) From your observations suggest two possible identities for the cation in FA 6. possible cations: …… and …… [1] (iii) Suggest a test that would allow you to determine which of the cations you suggested in (a)(ii) is present in FA 6. Carry out this test, record the result and hence identify the cation in FA 6. test . …… result . …… The cation present is …… . [2] (iv) From your observations in (a)(i) suggest two anions that could be present in FA 6 and give their formulae. possible anions: …… or ……[1] (v) Suggest an additional test that could be carried out to confirm the presence of one of the anions you suggested in (a)(iv). Carry out this test, record the result and hence state the identity of the anion. test . …… result . …… The anion present is …… . [2] (b) Half fill the 250 cm3 beaker with water and heat to approximately 80 °C. Turn off the Bunsen burner. This will be your hot water bath. FA 7 is an organic compound with an Mr between 40 – 57. (i) Carry out Test 2 and Test 3 on FA 7 and record your observations. The result for Test 1 is shown in the table. test observations Test 1 Add a small piece of sodium. no change Test 2 To a 0.5 cm depth of aqueous iodine in a test‑tube add aqueous sodium hydroxide dropwise until the yellow colour just disappears. Then add a few drops of FA 7 and shake the test‑tube. If no change is seen, warm the test‑tube in your hot water bath. Test 3 To a 1 cm depth of FA 7 in a test‑tube add a few drops of acidified potassium manganate(VII). Warm the test‑tube in your hot water bath. [2] (ii) Using the observations in (b)(i) suggest what can be deduced from each test about the functional groups present in FA 7. Test 1 …… Test 2 …… Test 3 …… [2] (iii) Use your deductions in (b)(ii) to suggest the identity of FA 7. FA 7 is …… . [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 16 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon 85.5 87.6 88.9 91.2 92.9 95.9 – 101.1 102.9 106.4 107.9 112.4 114.8 118.7 121.8 127.6 126.9 131.3 55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 lanthanoids Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon 132.9 137.3 178.5 180.9 183.8 186.2 190.2 192.2 195.1 197.0 200.6 204.4 207.2 209.0 – – – 87 88 89–103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson – – – – – – – – – – – – – – – – – 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium 138.9 140.1 140.9 144.4 – 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. 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