Chemistry 9701/54 October/November 2025: question paper and mark scheme

Question

A student uses a technique called the Winkler method to determine the mass of oxygen dissolved in a sample of water from a lake. Two solutions, X and Y, are prepared. Solution X is 2.30 mol dm–3 aqueous manganese(II) sulfate, MnSO4(aq). Solution Y is alkaline aqueous potassium iodide, KI(aq). (a) Calculate the mass of solid hydrated manganese(II) sulfate, MnSO4•H2O(s), needed to make 100.0 cm3 of solution X. Give your answer to two decimal places. mass of MnSO4•H2O(s) = …… g [1] (b) The student is given a small beaker containing the mass of MnSO4•H2O(s) calculated in (a). Describe how the student should prepare exactly 100.0 cm3 of solution X. Include the names and capacities of each piece of key apparatus used. Write your answer using a series of numbered steps. …… [3] * 0000800000003 * DFD 3 (c) Solution Y is prepared as follows. step 1 Place 100 cm3 of distilled water in a 250 cm3 beaker. step 2 Add about 8 g of solid sodium hydroxide, NaOH(s), and stir to dissolve. step 3 Cool the solution to room temperature using an ice‑bath. step 4 Repeat steps 2 and 3 until a total of 32 g of NaOH(s) has been dissolved. step 5 Dissolve about 14 g of potassium iodide, KI(s), into the solution formed in step 4. (i) Solution Y is corrosive. Other than wearing safety goggles, state one safety precaution that the student should take when preparing solution Y. …… [1] (ii) Suggest why the solution is cooled in step 3. …… [1] * 0000800000004 * DFD 4 (d) The student uses the following procedure to determine the mass of oxygen dissolved in a sample of water from the lake. step 1 Collect a 250 cm3 sample of lake water in a bottle. step 2 Add 1 cm3 of solution X and 1 cm3 of solution Y to the bottle. step 3 Immediately stopper the bottle, ensuring as little air as possible is trapped. step 4 Shake the bottle to mix its contents. A brown precipitate, manganese(III) hydroxide, Mn(OH)3(s), is formed. step 5 Add 1.5 cm3 of concentrated sulfuric acid to the contents of the bottle. The precipitate dissolves, and iodine is formed. step 6 Dilute this solution to exactly 500.0 cm3 using distilled water to form solution Z. step 7 Transfer 25.0 cm3 of solution Z into a conical flask, and titrate with 1.00 × 10–3 mol dm–3 aqueous sodium thiosulfate, Na2S2O3(aq). Add 1 cm3 of starch solution near to the end‑point. step 8 Repeat step 7 as many times as necessary. (i) Suggest why it is important to avoid trapping air inside the bottle in step 3. …… [1] (ii) Identify the piece of apparatus that the student should use to transfer the 25.0 cm3 of solution Z in step 7. …… [1] (iii) Suggest why starch solution is added in step 7. …… [1] * 0000800000005 * DFD 5 (e) The student records the results shown in Table 1.1. Table 1.1 rough titration 1 titration 2 titration 3 titration final burette reading / cm3 13.60 12.75 26.20 14.50 initial burette reading / cm3 0.00 0.05 13.15 1.35 titre / cm3 13.60 (i) Complete Table 1.1 and calculate the mean titre. mean titre = …… cm3 [2] (ii) Explain why the student does not need to carry out any further titrations. …… [1] (iii) Calculate the percentage error in the measurement of the titre for titration 3. Show your working. percentage error = …… % [1] * 0000800000006 * DFD 6 (f) The following equations show the reactions that take place during the procedure in (d). steps 2, 3 and 4 4Mn2+(aq) + 8OH–(aq) + O2(aq) + 2H2O(l) 4Mn(OH)3(s) step 5 2Mn(OH)3(s) + 2I–(aq) + 6H+(aq) I2(aq) + 6H2O(l) + 2Mn2+(aq) step 7 I2(aq) + 2S2O32–(aq) 2I–(aq) + S4O62–(aq) (i) Calculate the amount, in mol, of iodine, I2(aq), in 25.0 cm3 of solution Z. amount of I2(aq) = …… mol [1] (ii) Use your answer to (f)(i) and the equations given to calculate the amount, in mol, of dissolved oxygen, O2(aq), in 500.0 cm3 of solution Z. amount of O2(aq) in 500.0 cm3 of solution Z = …… mol [1] (iii) Dissolved oxygen content, mg dm–3, is the mass of oxygen dissolved in water. Use your answer to (f)(ii) to calculate the dissolved oxygen content in the lake water collected in step 1. [If you were unable to obtain an answer to (f)(ii), then use amount of O2(aq) in 500.0 cm3 of solution Z = 7.12 × 10–5 mol. This is not the correct answer.] dissolved oxygen content = …… mg dm–3 [1] [Total: 16] * 0000800000007 * DFD 7

Question

A student uses the following method to investigate the kinetics of the reaction between iodine and tin to produce tin(IV) iodide, SnI4. step 1 Rinse a block of tin with distilled water and then rinse it with propanone. step 2 Place 50 cm3 of a 0.400 mol dm–3 solution of iodine dissolved in methylbenzene in a 100 cm3 beaker. step 3 Suspend the block of tin from a three decimal place balance as shown in Fig. 2.1. Start a timer. step 4 Record the balance reading every 100 seconds. balance 4.979 wire iodine dissolved in methylbenzene block of tin Fig. 2.1 (a) (i) Suggest why the student rinses the block of tin with propanone after rinsing it with distilled water in step 1. …… [1] (ii) Suggest why water is not used as the solvent for iodine. …… [1] * 0000800000008 * DFD 8 (iii) Suggest why a three decimal place balance is more suitable than a two decimal place balance for this experiment. …… [1] (iv) Suggest a control experiment that could be used to verify that the loss in mass of tin is caused by reaction with iodine and not any other factor. …… [1] (b) The student’s results are shown in Table 2.1. Complete Table 2.1. Table 2.1 total mass of tin time / s balance reading / g reacted / g 0 4.979 0.000 100 4.910 200 4.859 300 4.761 400 4.688 500 4.620 [1] (c) (i) Use the results from Table 2.1 to plot a graph on the grid in Fig. 2.2 to show the relationship between total mass of tin reacted and time. Use a cross (×) to plot each data point. Draw a straight line of best fit. * 0000800000009 * DFD 9 0.40 0.35 0.30 0.25 total mass of tin 0.20 reacted / g 0.15 0.10 0.05 0.00 0 100 200 300 400 500 time / s Fig. 2.2 [2] (ii) Circle the point on the graph in Fig. 2.2 that you consider to be most anomalous. Suggest one reason why this anomaly may have occurred during this experimental procedure. Assume all measurements of mass are accurate. …… [1] * 0000800000010 * DFD 10 (d) Use your graph in Fig. 2.2 to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. These must be selected from your line of best fit. Give your gradient to three significant figures. coordinates 1 …… coordinates 2 …… gradient = …… [2] (e) Another student makes various concentrations of solutions of iodine dissolved in methylbenzene by dilution of the 0.400 mol dm–3 I2 solution. The student repeats the experiment at a different temperature using these solutions. Table 2.2 volume of volume of relative 0.400 mol dm–3 [I2] methylbenzene rate of I2 solution / mol dm–3 used / cm3 reaction used / cm3 100.0 0.0 0.400 4.76 0.300 3.57 0.200 2.35 0.100 1.15 (i) Complete Table 2.2 by adding the volumes of solutions that are mixed to make 100.0 cm3 of a solution of iodine dissolved in methylbenzene for each required concentration. [1] (ii) Identify the independent variable in this experiment. …… [1] * 0000800000011 * DFD 11 (iii) The student concludes that the rate equation for the reaction between iodine and tin is as follows. rate = k [I2]2 State whether the results support the student’s conclusion. Explain your answer using values from Table 2.2. …… [2] [Total: 14] 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 = 6.02 × 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 DFD 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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