9701 Chemistry November 2025 Question Paper 54

1 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] , ,

(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] , ,

(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] , ,

(e) The student records the results shown in Table 1.1. Table 1.1 rough titration titration 1 titration 2 titration 3 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] , ,

(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) + 2S2O3 2–(aq) 2I–(aq) + S4O6 2–(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] , ,

2 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. block of tin wire iodine dissolved in methylbenzene balance 4.979 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] , ,

(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 time / s balance reading / g total mass of tin 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. , , total mass of tin reacted / g time / s 0 100 200 300 400 500 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 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] , ,

(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 0.400 mol dm–3 I2 solution used / cm3 volume of methylbenzene used / cm3 [I2] / mol dm–3 relative rate of reaction 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] , ,

(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) , , Group The Periodic Table of Elements 1 H hydrogen 1.0 2 He helium 4.0 1 2 13 14 15 16 17 18 3 4 5 6 7 8 9 10 11 12 3 Li lithium 6.9 4 Be beryllium 9.0 atomic number atomic symbol Key name relative atomic mass 11 Na sodium 23.0 12 Mg magnesium 24.3 19 K potassium 39.1 20 Ca calcium 40.1 37 Rb rubidium 85.5 38 Sr strontium 87.6 55 Cs caesium 132.9 56 Ba barium 137.3 87 Fr francium – 88 Ra radium – 5 B boron 10.8 13 Al aluminium 27.0 31 Ga gallium 69.7 49 In indium 114.8 81 Tl thallium 204.4 6 C carbon 12.0 14 Si silicon 28.1 32 Ge germanium 72.6 50 Sn tin 118.7 82 Pb lead 207.2 22 Ti titanium 47.9 40 Zr zirconium 91.2 72 Hf hafnium 178.5 104 Rf rutherfordium – 23 V vanadium 50.9 41 Nb niobium 92.9 73 Ta tantalum 180.9 105 Db dubnium – 24 Cr chromium 52.0 42 Mo molybdenum 95.9 74 W tungsten 183.8 106 Sg seaborgium – 25 Mn manganese 54.9 43 Tc technetium – 75 Re rhenium 186.2 107 Bh bohrium – 26 Fe iron 55.8 44 Ru ruthenium 101.1 76 Os osmium 190.2 108 Hs hassium – 27 Co cobalt 58.9 45 Rh rhodium 102.9 77 Ir iridium 192.2 109 Mt meitnerium – 28 Ni nickel 58.7 46 Pd palladium 106.4 78 Pt platinum 195.1 110 Ds darmstadtium – 29 Cu copper 63.5 47 Ag silver 107.9 79 Au gold 197.0 111 Rg roentgenium – 30 Zn zinc 65.4 48 Cd cadmium 112.4 80 Hg mercury 200.6 112 Cn copernicium – 114 Fl flerovium – 116 Lv livermorium – 7 N nitrogen 14.0 15 P phosphorus 31.0 33 As arsenic 74.9 51 Sb antimony 121.8 83 Bi bismuth 209.0 8 O oxygen 16.0 16 S sulfur 32.1 34 Se selenium 79.0 52 Te tellurium 127.6 84 Po polonium – 9 F fluorine 19.0 17 Cl chlorine 35.5 35 Br bromine 79.9 53 I iodine 126.9 85 At astatine – 10 Ne neon 20.2 18 Ar argon 39.9 36 Kr krypton 83.8 54 Xe xenon 131.3 86 Rn radon – 113 Nh nihonium – 115 Mc moscovium – 117 Ts tennessine – 118 Og oganesson – 21 Sc scandium 45.0 39 Y yttrium 88.9 57–71 lanthanoids 89–103 actinoids 57 La lanthanum 138.9 89 Ac lanthanoids actinoids actinium – 58 Ce cerium 140.1 90 Th thorium 232.0 59 Pr praseodymium 140.9 91 Pa protactinium 231.0 60 Nd neodymium 144.2 92 U uranium 238.0 61 Pm promethium – 93 Np neptunium – 62 Sm samarium 150.4 94 Pu plutonium – 63 Eu europium 152.0 95 Am americium – 64 Gd gadolinium 157.3 96 Cm curium – 65 Tb terbium 158.9 97 Bk berkelium – 66 Dy dysprosium 162.5 98 Cf californium – 67 Ho holmium 164.9 99 Es einsteinium – 68 Er erbium 167.3 100 Fm fermium – 69 Tm thulium 168.9 101 Md mendelevium – 70 Yb ytterbium 173.1 102 No nobelium – 71 Lu lutetium 175.0 103 Lr lawrencium – , ,