CIE Mar 2016 v2 Paper 5 Q2

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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. PMT thermometer metal can draught shield ethanol clamp water spirit burner 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 g1 K1] [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 0.391 0.488 0.506 0.559 0.727 0.597 0.410 0.681 19.5 23.6 24.5 26.9 33.6 31.1 20.3 31.7 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0UCLES 2016 9701/52/F/M/16 [2]<br /> (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. PMT 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 amount of ethanol burned / mol [2] (c) Write the number of the experiment which gave the result which was most anomalous.[1] J k / y g r e n eUCLES 2016 9701/52/F/M/16 [Turn over<br /> (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 usedPMT gradient =kJ mol1 [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 mol1. 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 mol1. Suggest a reason why the errors calculated in (i) do not fully account for the difference between the students value and the accepted value for enthalpy change of combustion, 1370 kJ mol1.[1] [Total: 10] 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.UCLES 2016 9701/52/F/M/16<br />

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