Cambridge A Level Chemistry 9701 — 2016 Feb/March Paper 5 · Variant 2

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. You may lose marks if you do not show your working or if you do not use appropriate units. Use of a Data Booklet is unnecessary. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. CHEMISTRY 9701/52 Paper 5 Planning, Analysis and Evaluation February/March 2016 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level This document consists of 8 printed pages. [Turn over IB16 03_9701_52/4RP © UCLES 2016 *8656660162*

2 9701/52/F/M/16 © UCLES 2016 1 Propanone, CH3COCH3, is an organic liquid which is soluble in water. Aqueous propanone reacts with aqueous iodine. The reaction is catalysed by H+(aq) ions. CH3COCH3(aq) + I2(aq) → CH3COCH2I(aq) + HI(aq) The order of reaction with respect to iodine can be determined experimentally. An experiment is carried out using the following solutions. • solution A, 25.0 cm3 of 1.00 mol dm–3 CH3COCH3(aq) • solution B, 25.0 cm3 of 1.00 mol dm–3 H2SO4(aq) • solution C, 50.0 cm3 of 0.200 mol dm–3 I2(aq) The solutions are mixed to start the reaction. At certain time intervals, a 10.0 cm3 portion of the mixture is withdrawn and transferred to a conical flask containing excess sodium hydrogencarbonate, NaHCO3(aq). This prevents any further significant reaction taking place by removing the H+(aq) ions. The concentration of unreacted I2(aq) in each 10.0 cm3 portion of the mixture can then be determined by titration with aqueous thiosulfate ions, S2O3 2–(aq). (a) State the size and type of apparatus needed to prepare a suitable volume of a standard solution of 1.00 mol dm–3 CH3COCH3(aq) from liquid propanone. Calculate the mass of propanone needed to prepare this standard solution. [Ar: C, 12.0; H, 1.0; O, 16.0] apparatus … mass of propanone … g [3]

3 9701/52/F/M/16 © UCLES 2016 [Turn over (b) Solutions A, B and C need to be added in a specific order and the clock started as the third solution is added. (i) Suggest the best order of adding the solutions. 1 … 2 … 3 … [1] (ii) Explain your choice. … … [1] (c) Each 10.0 cm3 portion of mixture removed from the main reaction is added to a separate solution of sodium hydrogencarbonate, NaHCO3(aq), in a conical flask to remove H+(aq) ions. (i) Which piece of apparatus should be used to transfer each 10.0 cm3 portion of mixture to the conical flask? … [1] (ii) Suggest two reasons why NaHCO3(aq) is preferred to NaOH(aq) as the reagent used to remove H+(aq) ions. reason 1 … … reason 2 … … [2]

4 9701/52/F/M/16 © UCLES 2016 (d) The unreacted iodine in each 10.0 cm3 portion of the mixture is titrated against 0.100 mol dm–3 aqueous thiosulfate ions, S2O3 2–(aq), to determine the concentration of I2(aq) in the mixture at the time that the 10.0 cm3 portion was withdrawn. I2(aq) + 2S2O3 2–(aq) → 2I–(aq) + S4O6 2–(aq) (i) A 10.0 cm3 portion of mixture is removed at time = 0. This is before any of the 0.200 mol dm–3 I2(aq) had reacted. Calculate the volume of 0.100 mol dm–3 S2O3 2–(aq) needed to react with the iodine present in this 10.0 cm3 portion of mixture. volume 0.100 mol dm–3 S2O3 2–(aq) = … cm3 [3] (ii) Suggest the name of a suitable indicator to use in the titration and state its colour change. indicator … colour change … [2] (e) State two variables which must be recorded in this experiment. For each variable, state the units. variable 1 … units … variable 2 … units … [2] (f) State one other variable which must be controlled in this experiment. … [1]

5 9701/52/F/M/16 © UCLES 2016 [Turn over (g) The order of reaction with respect to iodine is expected to be first order. (i) Use the axes below to draw a sketch graph of how the concentration of iodine changes during the experiment. Label both axes. [2] (ii) How could the graph be used to prove that the order of reaction with respect to iodine is first order? … … … [1] (h) A student suggested that the temperature at which the experiment was carried out would affect the order of reaction with respect to iodine. State if the student was correct and explain your answer. … … [1] [Total: 20]

6 9701/52/F/M/16 © UCLES 2016 2 A student carried out a series of experiments to determine the enthalpy change of combustion of ethanol, C2H5OH. A diagram of the apparatus is shown below. clamp water spirit burner thermometer metal can draught shield ethanol The ethanol in the spirit burner was burned to heat a measured mass of water in the metal can. The student recorded the initial and final mass of ethanol and the initial and final temperature of the water for each experiment. (a) Process the results in the table to calculate the amount of ethanol burned and the energy transferred to the water in each experiment. Record all answers to three significant figures. [Specific heat capacity of water, c = 4.18 J g–1 K–1] [Ar: C, 12.0; H, 1.0; O, 16.0] experiment number mass of ethanol burned / g temperature change / °C mass of water heated / g amount of ethanol burned / mol energy transferred to the water / kJ 1 0.391 19.5 40.0 2 0.488 23.6 40.0 3 0.506 24.5 40.0 4 0.559 26.9 40.0 5 0.727 33.6 40.0 6 0.597 31.1 40.0 7 0.410 20.3 40.0 8 0.681 31.7 40.0 [2]

7 9701/52/F/M/16 © UCLES 2016 [Turn over (b) Plot a graph on the grid below to show how the energy transferred to the water varies with the amount of ethanol burned. Draw the line of best fit. 0.008 0.009 0.010 0.011 0.012 amount of ethanol burned / mol energy / kJ 0.013 0.014 0.015 0.016 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 [2] (c) Write the number of the experiment which gave the result which was most anomalous. … [1]

8 9701/52/F/M/16 © UCLES 2016 Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge. (d) The gradient of the graph gives the magnitude of the enthalpy change of combustion of ethanol. Determine the gradient of your graph. State the co-ordinates of the two points you used for your calculation. Record the value of the gradient to three significant figures. co-ordinates of two points used … … gradient = … kJ mol–1 [2] (e) Under the same conditions of temperature and pressure as these experiments, the accepted value for the enthalpy change of combustion of ethanol is –1370 kJ mol–1. Explain why this value is a negative number. … [1] (f) (i) Calculate the maximum percentage error in the measurement of each mass used in experiment 1. mass measured maximum error in a single reading maximum percentage error / % 0.391 g of ethanol burned 0.0005 g 40.0 g of water 0.05 g [1] (ii) Another student repeated the experiments using the method described under the same conditions. The value obtained for the enthalpy change of combustion of ethanol was –612 kJ mol–1. Suggest a reason why the errors calculated in (i) do not fully account for the difference between the student’s value and the accepted value for enthalpy change of combustion, –1370 kJ mol–1. … … [1] [Total: 10]

® IGCSE is the registered trademark of Cambridge International Examinations. CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the March 2016 series 9701 CHEMISTRY 9701/52 Paper 5 (Planning, Analysis and Evaluation), maximum raw mark 30 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the March 2016 series for most Cambridge IGCSE® and Cambridge International A and AS Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – March 2016 9701 52 © Cambridge International Examinations 2016 question expected answer mark 1 (a) M1 (apparatus mark) volumetric flask in range 25–250 cm3; M2 mol propanone = 1.00 × (flask volume / 1000); e.g. mol of propanone = 1.00 × 25 / 1000 = 0.025 mol M3 M2 × 58.0; e.g.0.025 × 58.0 = 1.45 g [3] (b) (i) B must be added before first or second reactant [1] (ii) the reactants are A and C so one of these must be mixed last; or the reaction must not start before all three substances are present; [1] (c) (i) (10 cm3) pipette [1] (ii) M1 NaHCO3 will effervesce so when effervescence finishes it shows that all H+ ions have been removed; M2 NaOH will react with I2 / CH3COCH3 / reactants; [2] (d) (i) M1 mol I2 = (10 / 100) × 0.200 × (50 / 1000) = 1.(00) × 10–3 mol; M2 mol S2O3 2– = 2 × 1.00 × 10–3 = 2.(00) × 10–3 mol; M3 volume 0.100 mol dm–3 S2O3 2– = (1000 × 2.00 × 10–3) / 0.100 = 20(.0) cm3; [3] (ii) indicator = starch; colour change = blue-black to colourless; [2] (e) time and units of s; volume of thiosulfate and units of cm3; [2] (f) temperature; [1] (g) (i) M1 (labels) x-axis = time y-axis = concentration of iodine M2 curved line decreasing from left to right starting from x = 0 [2]

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – March 2016 9701 52 © Cambridge International Examinations 2016 question expected answer mark (ii) idea of constant half-life: determine at least two half-lives from the graph and ensure that they are the same; or half-lives determined from the graph should be constant; or determine the gradient (rate) at different points on the graph and plot rate v. concentration to determine if the plot is linear and goes through the origin; [1] (h) (incorrect and) half-life will still be constant; or temperature has no effect upon order (of reaction); [1] 2 (a) M1 column amount of ethanol burned correctly completed M2 column energy transferred to the water correctly completed experiment number amount of ethanol burned / mol energy transferred to the water / kJ 1 0.00850 3.26 2 0.0106 3.95 3 0.0110 4.10 4 0.0122 4.50 5 0.0158 5.62 6 0.0130 5.20 7 0.00891 3.39 8 0.0148 5.30 [2] (b) M1 at least eight correctly plotted points; M2 correct straight line; [2] (c) experiment 6; [1] (d) M1 co-ordinates, e.g. (0.0106, 3.95) and (0.0158, 5.62); M2 gradient correctly calculated from points, e.g. 321 (kJ mol–1); [2] (e) because the reaction is exothermic; [1] (f) (i) ((2 × 0.0005) / 0.391) × 100 = 0.256% and (0.05 / 40.0) × 100 = 0.125%; [1]

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – March 2016 9701 52 © Cambridge International Examinations 2016 question expected answer mark (ii) (total) errors in weighing do not account for the (large) error in enthalpy change determined; or heat loss (is more significant); [1]