Chemistry 9701/52 May/June 2025: question paper and mark scheme

Question

Activated carbon is a form of carbon with the ability to adsorb solutes from solutions. The adsorption of ethanedioic acid molecules, (COOH)2, from dilute ethanedioic acid, (COOH)2(aq), onto the surface of activated carbon is studied in a series of experiments. Before beginning the experiment, 500.0 cm3 of 0.139 mol dm–3 (COOH)2(aq), solution X, is made. The activated carbon is placed in an oven at 120 °C for three hours. The experimental procedure involves the following steps. step 1 Prepare 100.0 cm3 of 0.00556 mol dm–3 (COOH)2(aq) from solution X. step 2 Transfer 50.0 cm3 of the 0.00556 mol dm–3 (COOH)2(aq) into a conical flask. step 3 Add 0.500 g of activated carbon to the conical flask and start a stopwatch. step 4 Shake the flask and immediately remove a 5.0 cm3 sample from the flask. Determine the mass of non-adsorbed (COOH)2 in the sample using chromatography. step 5 Repeat step 4 at suitable time intervals until there is no further change in the mass of non-adsorbed (COOH)2 in the sample. (a) Solid ethanedioic acid has the formula (COOH)2•2H2O. Calculate the mass of (COOH)2•2H2O(s) required to prepare 500.0 cm3 of 0.139 mol dm–3 (i) (COOH)2(aq), solution X. mass = …… g [1] (ii) The mass of (COOH)2•2H2O(s) calculated in (a)(i) is placed into a 100 cm3 beaker. Describe the steps taken to prepare 500.0 cm3 of 0.139 mol dm–3 (COOH)2(aq). Give the name and capacity of any apparatus used. Write your answer using a series of numbered steps. …… [3] (b) (COOH)2•2H2O(s) is corrosive. Other than wearing eye protection and a lab coat, state one safety precaution that should be taken when using (COOH)2•2H2O(s). …… [1] (c) Suggest why the activated carbon is placed in the oven before use. …… [1] (d) In step 1, solution X is diluted to a concentration of 0.00556 mol dm–3. Calculate the volume of solution X needed to make 100.0 cm3 of 0.00556 mol dm–3 (COOH)2(aq). volume of solution X = …… cm3 [1] (e) Identify the most appropriate piece of equipment to transfer 50.0 cm3 of diluted (COOH)2(aq) in step 2. …… [1] (f) Suggest a reason why the conical flask is shaken in step 4. …… [1] (g) The results of the experiment are shown in Table 1.1. Table 1.1 mass of (COOH)2 adsorbed mass of non-adsorbed by activated carbon in time, t / min (COOH)2 in 5.0 cm3 sample 5.0 cm3 sample / mg / mg 0 2.50 0.00 5 1.90 15 1.52 30 1.43 45 0.99 60 0.88 90 0.81 120 0.80 150 0.80 (i) Complete Table 1.1. [1] (ii) Plot a graph on the grid in Fig. 1.1 to show the relationship between mass of (COOH)2 adsorbed by activated carbon in 5.0 cm3 sample and time, t. Use a cross (×) to plot each data point. Draw a curved line of best fit. [2] (iii) Identify the independent variable. …… [1] (iv) Suggest one variable that needs to be controlled that is not stated in the experimental procedure. …… [1] (v) Circle the one point on the graph that you consider to be most anomalous. Explain the error in timing that may have led to this anomalous point. …… [1] 1.8 1.6 1.4 1.2 mass of (COOH)2 1.0 adsorbed by activated carbon in 5.0 cm3 sample / mg 0.8 0.6 0.4 0.2 0 0 20 40 60 80 100 120 140 160 time, t / min Fig. 1.1 (h) The experiment is repeated using different concentrations of (COOH)2(aq) prepared in step 1. The results are shown in Table 1.2. Table 1.2 1 2 3 4 5 me mi / mg me / mg (mi – me) / mg qe / mg g–1 qe / g 2.5 0.80 1.70 34.0 0.0235 5.0 2.10 2.90 58.0 0.0362 7.5 4.03 3.47 69.4 0.0581 10.0 6.41 3.59 71.8 0.0893 12.5 8.87 3.63 72.6 0.1222 mi is the initial mass of (COOH)2 in 5.0 cm3 sample. me is the mass of non-adsorbed (COOH)2 in the final 5.0 cm3 sample at the end of step 5. qe is the mass of (COOH)2 adsorbed per gram of activated carbon. m (i) A plot of q e against me gives the line of best fit shown in Fig. 1.2. e Use Fig. 1.2 to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. coordinates 1 …… coordinates 2 …… Include units in your answer. gradient = …… units = …… [3] (ii) The adsorption parameter, q0, is the maximum mass of (COOH)2 adsorbed per gram of activated carbon. The equation of the line of best fit plotted in Fig. 1.2 is shown. me me qe = q0 + constant Use the gradient determined in (h)(i) to calculate the adsorption parameter, q0. [If you were unable to determine an answer to (h)(i), then use the value 0.0136 for the gradient. This is not the correct answer.] q0 = …… mg g–1 [1] 0.14 0.12 0.10 0.08 me qe / g 0.06 0.04 0.02 0 0 2 4 6 8 10 me / mg Fig. 1.2 (i) The experiment is repeated and the value of q0 is calculated to be 78.1 mg g–1. The total percentage error from the experimental procedure is 6.5%. The data book value of q0 is 86.0 mg g–1. Use this information to determine whether the error in the repeated experiment could be accounted for by experimental errors or is caused by other factors. Show your working. …… [1] [Total: 20]

Question

The enthalpy change of combustion, ∆Hc, of butane, C4H10, can be determined using the apparatus shown in Fig. 2.1. thermometer metal can water tripod gas burner tap gas container of butane Fig. 2.1 The following steps are carried out. step 1 Use a 500 cm3 measuring cylinder to transfer 320 cm3 of water into a metal can. step 2 Place a thermometer into the water. Record the initial temperature of the water in the metal can. step 3 Weigh the gas container with burner and record the initial mass. step 4 Set up the apparatus as shown in Fig. 2.1. step 5 Light the burner and allow the flame to heat the water in the metal can for three minutes. step 6 Switch off the burner and record the maximum temperature reached. step 7 When cool, reweigh the gas container with burner and record the final mass. The results are shown in Table 2.1. Table 2.1 initial maximum change in initial mass of final mass of mass of temperature temperature temperature of gas container gas container butane of water / °C of water / °C water, ∆T / °C with burner / g with burner / g burned / g 19.3 76.6 183.56 181.46 (a) Complete Table 2.1. Record your answers to the appropriate number of decimal places. [2] (b) Use the relationship q = mc∆T to calculate the energy, q, in J, gained by the water. 1.00 cm3 of water has a mass of 1.00 g. q = …… J [1] (c) Calculate the enthalpy change of combustion, ∆Hc, of butane, in kJ mol–1. Give your answer to three significant figures. ∆Hc = …… kJ mol–1 [2] (d) Without changing the apparatus, suggest what should be done in step 6 before recording the maximum temperature reached to improve the experimental procedure. …… [1] (e) The 500 cm3 measuring cylinder has graduations every 5 cm3. Calculate the percentage error in the measurement of the volume of water. Show your working. percentage error = …… % [1] (f) A student suggests that the value calculated in (c) is different from the actual value of ∆Hc of butane because of heat lost during the experiment. Suggest one change to the apparatus that would reduce the heat lost. …… [1] (g) The experiment was repeated but the burner was switched off after only two minutes. (i) Suggest why this might contribute to a reduction in the accuracy of ∆Hc of butane. …… [1] (ii) Suggest why this might contribute to an increase in the accuracy of ∆Hc of butane. …… [1] [Total: 10] 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 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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