Chemistry 9701/34 October/November 2022: question paper and mark scheme

Question

You are to determine the enthalpy change for a metal displacement reaction using a known volume and concentration of copper(II) sulfate and an excess of powdered zinc. Cu2+(aq) + Zn(s) → Zn2+(aq) + Cu(s) FB 1 is 0.80 mol dm–3 copper(II) sulfate, CuSO4. FB 2 is zinc, Zn. (a) Method ● Weigh the container with FB 2. Record the mass. ● Support the cup in the 250 cm3 beaker. ● Use the 50 cm3 measuring cylinder to transfer 30.0 cm3 of FB 1 into the cup. ● Place the thermometer in the solution. Measure and record the initial temperature of the solution. This is the temperature at time zero, t = 0. ● Start timing and do not stop the clock until the whole experiment has been completed. ● Measure and record the temperature of the solution every half minute for 2 minutes. ● At time t = 2 12 minutes tip all the FB 2 into the solution and stir the mixture. ● Measure and record the temperature of the mixture at t = 3 minutes and every half minute until t = 9 minutes. Stir the mixture between thermometer readings. ● Weigh the container with any residue of FB 2. Record the mass. ● Calculate and record the mass of FB 2 added to the solution. Results I II 1 time / minutes 0 2 1 1 12 2 2 12 3 3 12 4 III temperature / °C IV time / minutes 4 12 5 5 12 6 6 12 7 7 12 8 8 12 9 temperature / °C [4] (b) (i) Plot a graph of temperature on the y-axis against time on the x-axis on the grid. The scale for temperature should extend 5 °C above your highest recorded temperature. You will use this graph to determine the theoretical maximum temperature rise at 2 12 minutes. [3] (ii) Draw two lines of best fit through the points on your graph. The first line should be for the temperature before adding FB 2 and the second for the cooling of the mixture. Extrapolate the two lines to 2 12 minutes. Draw a vertical line at 2 12 minutes. Determine the theoretical rise in temperature at this time. theoretical rise in temperature at 2 12 minutes = …… °C [2] (c) Calculations (i) Calculate the amount, in mol, of copper(II) sulfate in FB 1 added to the cup in (a). amount of CuSO4 = …… mol [1] (ii) Show that the amount of zinc you added was in excess. [1] (iii) Use your answer to (b)(ii) to calculate the heat energy, in joules, given out when FB 2 is added to FB 1. heat energy = …… J [1] (iv) Calculate the enthalpy change of reaction, ∆Hr, for the reaction carried out in (a). Show your working. ∆Hr = …… …… kJ mol–1 sign value[1] (d) A student carries out two further experiments using method (a). In the first experiment, FB 1 is made using a fresh sample of hydrated copper(II) sulfate, CuSO4•5H2O. In the second experiment, FB 1 is made using an old sample of hydrated copper(II) sulfate. The same mass of solid is used to make the solutions in these experiments. In the second experiment, the student obtains a value for ∆Hr that is 10.7 kJ mol–1 greater in magnitude than the value from the first experiment. Suggest what may be deduced about the formula of the old sample of hydrated copper(II) sulfate. The water of crystallisation is greater than 5. The formula, CuSO4•5H2O, is correct. The water of crystallisation is less than 5. Tick the appropriate box and explain your answer. . …… . …… . …… [2] [Total: 15]

Question

Many metal carbonates, such as copper(II) carbonate, exist as basic carbonates. These are a combination of the metal carbonate and a base of the metal. A bottle is labelled copper(II) carbonate, CuCO3. You will carry out a gravimetric experiment to see whether the formula given is correct. CuCO3(s) → CuO(s) + CO2(g) FB 3 is copper(II) carbonate and may have the formula CuCO3. (a) Method ● Weigh a crucible with its lid. Record the mass. ● Add 1.50–1.80 g of FB 3 to the crucible. ● Weigh the crucible and lid with FB 3. Record the mass. ● Place the crucible on the pipe-clay triangle. Heat the crucible, with the lid on, gently for approximately 1 minute and then strongly for another minute. ● Remove the lid. Heat the crucible strongly for about 4 minutes. ● Replace the lid and leave the crucible and residue to cool for at least 5 minutes. While the crucible is cooling you may wish to begin work on Question 3. ● Reweigh the crucible and contents with its lid. Record the mass. ● Calculate and record the mass of FB 3 added to the crucible. ● Calculate and record the mass of the residue obtained. Keep the residue for use in 2(d). Results I II III IV [4] (b) Calculations (i) The residue obtained in (a) is copper(II) oxide. Calculate the amount, in mol, of copper(II) oxide formed on heating. amount of CuO = …… mol [1] (ii) Calculate the mass lost on heating the copper carbonate. mass lost = …… g Assuming the formula for FB 3 is CuCO3, calculate the amount, in mol, of carbon dioxide lost on heating. amount of CO2 = …… mol [1] (iii) Use your answers to (b)(i) and (b)(ii) to explain whether the formula of FB 3 is CuCO3. . …… . …… [1] (c) Another bottle of copper(II) carbonate was labelled basic copper(II) carbonate but part of the label giving the formula had been torn and only showed ‘CuCO3•Cu...’. Suggest a formula for basic copper(II) carbonate. (d) (i) It is possible that FB 3 did not decompose fully on heating in (a). Explain how you would change the method used to ensure decomposition was complete. . …… . …… [1] (ii) Select a reagent to use to test whether your sample of FB 3 has decomposed completely. reagent …… Carry out your test on the residue from (a). Record your observations. State your conclusion. . …… . …… [2] [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.

Question

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. (a) FB 4 is an aqueous solution containing one cation and one anion, both of which are listed in the Qualitative analysis notes. FB 5 is an aqueous solution of an organic compound which contains a functional group which is one of an alcohol, an aldehyde or a carboxylic acid. (i) For each test use a 1 cm depth of FB 4 in a test-tube. Record all your observations. test observations Test 1 Add aqueous ammonia, then add aqueous EDTA. Test 2 Add a 2 cm depth of aqueous EDTA, then add a few drops of aqueous sodium hydroxide, then add a 1 cm depth of FB 5 and place the test-tube in the hot water bath. test observations Test 3 Add a strip of magnesium ribbon and leave the test-tube for 1 minute. [5] (ii) The anion in FB 4 is either a halide or an anion containing sulfur. Select reagents to positively identify the anion. Carry out your tests and record the reagents used and your observations in a suitable form below. [3] (iii) Identify the compound in FB 4 from your observations. The formula of FB 4 is …… . [1] (iv) Give an ionic equation for a reaction in Test 3. Include state symbols. . …… [1] (b) Reheat your water bath to boiling then switch off your Bunsen burner. Prepare Tollens’ solution for use in Test 1 as follows: Place a 12 cm depth of aqueous silver nitrate in a test-tube. Add 1 or 2 drops of aqueous sodium hydroxide to form a brown precipitate. Shake the tube then add aqueous ammonia dropwise with shaking until the precipitate just dissolves. When you have completed Test 1 pour the contents of the test-tube down the sink with plenty of water and rinse the test-tube. (i) Use a 1 cm depth of FB 5 in a test-tube for each of the following tests. test observations Test 1 Add a 1 cm depth of Tollens’ solution and place the test-tube in the hot water bath. Test 2 Add 1 or 2 drops of acidified aqueous potassium manganate(VII) and place the test-tube in the hot water bath. Test 3 Add a 1 cm depth of aqueous sodium carbonate. [3] (ii) FB 5 contains a functional group which is either an alcohol, an aldehyde or a carboxylic acid. State which functional group is present. Explain your answer. . …… . …… [1] [Total: 14] 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