Chemistry 9701/34 May/June 2025: question paper and mark scheme

Question

Iron is an element that is essential in the human diet. Some people need to take iron supplement tablets to ensure an adequate intake of iron. You will investigate the mass of iron in an iron supplement tablet by titrating a solution with potassium manganate(VII). Fe2+(aq) Fe3+(aq) + e– MnO4–(aq) + 8H+(aq) + 5e– Mn2+(aq) + 4H2O(l) FB 1 is an aqueous solution of iron supplement tablets made by dissolving 14 tablets in 1.00 dm3 of solution. The iron in each tablet is iron(II) sulfate, FeSO4•7H2O. FB 2 is 0.0100 mol dm–3 acidified aqueous potassium manganate(VII), KMnO4. FB 3 is dilute sulfuric acid, H2SO4. (a) Method • Fill a burette with FB 2. • Pipette 25.0 cm3 of FB 1 into a conical flask. • Use the 25 cm3 measuring cylinder to add 10.0 cm3 of FB 3 to the conical flask. • 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 in the space below, all your burette readings and the volume of FB 2 added in each accurate titration. Rinse the burette with distilled water and leave to drain while you continue Question 1. Results 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 FB 1 required …… cm3 of FB 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 amount, in mol, of manganate(VII) ions in the volume of FB 2 in (b). amount of MnO4– = …… mol [1] (iii) Use your answer to (c)(ii) and the equations at the start of the question to calculate the concentration, in mol dm–3, of iron(II) ions in FB 1. concentration of Fe2+ = …… mol dm–3 [1] (iv) Use your answer to (c)(iii) to calculate the concentration, in g dm–3, of iron(II) ions in FB 1. concentration of Fe2+ = …… g dm–3 [1] (v) The manufacturer of the iron supplement tablets used to make FB 1 claims that each tablet contains a minimum of 150 mg of Fe2+. Use your answer to (c)(iv) and the information given about FB 1 to determine whether this claim is correct. Show your working. [1] (d) A student used all the FB 3 and suggests that dilute hydrochloric acid would be a suitable replacement. Suggest whether the student is correct or not. Explain your answer. …… [1] [Total:14]

Question

The reaction between an acid and an alkali is exothermic. You will carry out a neutralisation experiment to determine the enthalpy change involved. You will mix different volumes of an acid with a fixed volume of an alkali and measure the temperature rises that occur. FB 4 is aqueous sodium hydroxide, NaOH. FB 5 is 2.00 mol dm–3 hydrochloric acid, HCl . (a) Method • Use the thermometer to measure the initial temperature of FB 4. Record this initial temperature in the space for results. • Support the cup in the 250 cm3 beaker. • Fill one burette with FB 5. Label the burette FB 5. • Fill the other burette with distilled water. Experiment 1 • Use the 10 cm3 pipette to transfer 10.0 cm3 of FB 4 into the cup. • Add 9.00 cm3 of distilled water from the burette to the same cup. • Add 1.00 cm3 of FB 5 from the other burette to the same cup. • Stir the mixture and use the thermometer to measure the maximum temperature. If necessary, tilt the cup so that the solution covers the bulb of the thermometer. • Record the maximum temperature in Table 2.1. • Empty, rinse and dry the cup ready for use in further experiments. Further experiments Repeat this method for Experiments 2–5, using 10.0 cm3 of FB 4 and the volumes of water and FB 5 shown in Table 2.1. In each case, measure and record the maximum temperature. Carry out two further experiments, Experiments 6 and 7, which will enable you to determine more precisely the volume of FB 5 that gives the largest maximum temperature. Record your measurements in Table 2.1. Results initial temperature of FB 4 = …… °C Table 2.1 volume of water volume of FB 5 maximum experiment / cm3 / cm3 temperature / °C 1 9.00 1.00 2 7.00 3.00 3 5.00 5.00 4 3.00 7.00 I 5 1.00 9.00 II 6 III 7 IV [4] (b) (i) Plot a graph of the maximum temperature (y‑axis) against the volume of FB 5 (x‑axis) on the grid. The scale on the y‑axis should be suitable for temperature readings to be 2 °C above the largest maximum temperature. Label any points you consider to be anomalous. Draw two lines of best fit, the first for the increase in maximum temperature and the second for after the largest maximum temperature has been reached. Extrapolate both lines so that they intersect. [4] I II III IV (ii) Use the intersection on your graph in (b)(i) to determine the volume of FB 5 required to neutralise 10.0 cm3 of FB 4. volume of FB 5 = …… cm3 [1] (c) Calculations (i) Calculate the amount, in mol, of hydrochloric acid in the volume of FB 5 in (b)(ii). (If you were unable to determine an answer to (b)(ii), use 5.10 cm3 as the volume of FB 5. This may not be the correct answer.) amount of HCl = …… mol Deduce the amount, in mol, of sodium hydroxide in 10.0 cm3 of FB 4. amount of NaOH = …… mol [1] (ii) Calculate the energy change, in J, when the amounts of reagents in (c)(i) neutralise each other. Show your working. energy change = …… J [1] (iii) Use your answer to (c)(ii) to calculate the enthalpy change, in kJ mol–1, when one mole of FB 4 is neutralised by one mole of FB 5. enthalpy change = …… …… kJ mol–1 [1] sign value [Total: 12] 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. If a solid is heated, a hard‑glass test‑tube must be used. Rinse and reuse test‑tubes and boiling tubes where possible. No additional tests should be attempted.

Question

(a) (i) FB 6, FB 7 and FB 8 are aqueous solutions of different compounds that each contain at least one oxygen atom. Carry out the following tests and record your observations in Table 3.1. Three of the tests have been done for you. Use a 1 cm depth of solution in a test‑tube for each test. Table 3.1 observations test FB 6 FB 7 FB 8 Test 1 Add a small spatula measure No change. No change. of manganese(IV) oxide. Test 2 Add a 1 cm length of magnesium. No change. Test 3 Add a few drops of aqueous iron(II) sulfate. [4] (ii) Use your observations in Table 3.1 to suggest a possible formula for each of FB 6, FB 7 and FB 8. FB 6 …… FB 7 …… FB 8 …… [2] (b) FB 9 contains two anions and two cations, three of which are listed in the Qualitative analysis notes. (i) To a small spatula measure of FB 9 in a test‑tube, add a 2 cm depth of dilute nitric acid. Record your observations. Keep the resulting solution for the test in (b)(ii). …… [2] (ii) To the solution from (b)(i), add a few drops of aqueous silver nitrate. Then add excess aqueous ammonia. Record your observations. …… [1] (iii) Make an aqueous solution of FB 9 by adding a 5 cm depth of distilled water to a spatula measure of FB 9 in a test‑tube. Carry out the following tests on the aqueous solution of FB 9 and record your observations in Table 3.2. Table 3.2 test observations Test 1 To a 1 cm depth in a boiling tube, add aqueous sodium hydroxide, then warm. Test 2 To a 1 cm depth in a test‑tube, add a few drops of dilute hydrochloric acid, then add a few drops of aqueous chlorine. Empty and rinse the test‑tube with water immediately after use. [2] (iv) Use your observations in (b)(i), (b)(ii) and Table 3.2 to deduce the formulae of the cations and anions in FB 9. If you are unable to identify an ion, write ‘unknown’. cations …… and …… anions …… and …… [2] (v) Write an ionic equation for the reaction in (b)(ii). Include state symbols. …… [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), off‑white ppt. rapidly turning brown off‑white ppt. rapidly turning brown Mn2+(aq) 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 F = 9.65 × 104 C mol–1 Faraday constant Avogadro constant L = 6.02 × 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 138.9 140.1 140.9 144.2 – 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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