CIE Nov 2017 v3 Paper 5 Q2

Answers available below

Dilute sulfuric acid, H2SO4(aq), can be electrolysed using platinum electrodes and a direct current. Hydrogen gas is produced at the cathode and oxygen gas is produced at the anode. The two gases are collected separately in burettes filled with dilute sulfuric acid placed over each electrode. PMT 50.0 cm3 mark burette 1 burette 2 0.0 cm3 mark dilute sulfuric acid platinum electrode reaction at electrode in burette 1: 2H+(aq) + 2e reaction at electrode in burette 2: H2O(l) H2(g) 1 2O2(g) + 2H+(aq) + 2eUCLES 2017 9701/53/O/N/17 [Turn over<br /> PMT The production of hydrogen gas over time can be measured, and the data used to determine the charge of one mole of electrons, known as the Faraday constant, F. (a) The volumes of hydrogen gas produced during the electrolysis process are recorded in the table. Process the results to calculate the volume of hydrogen gas produced, in cm3, and the charge passed, in coulombs, C. charge (C) = current (A)time (s) The current was kept constant at 0.80 A. time / s reading on burette 1 / cm3 volume of hydrogen gas produced / cm3 charge passed / C 0.00 50 100 150 200 250 300 350 400 450 46.20 41.20 36.20 31.45 25.80 20.80 16.40 11.45 6.80 1.50 [2]UCLES 2017 9701/53/O/N/17<br /> m c / d e c u d o r p s a g n e g o r d y h e m u o v (b) Plot a graph on the grid to show the relationship between volume of hydrogen gas produced and charge passed. Use a cross () to plot each data point. Draw the straight line of best fit. PMT 44.00 40.00 36.00 32.00 28.00 24.00 20.00 16.00 12.00 8.00 4.00 0.00 40 80 120 160 200 charge passed / C 240 280 320 360UCLES 2017 9701/53/O/N/17 [2] [Turn over<br /> PMT 10 (c) Do you think the results obtained in (a) are reliable? Explain your answer.[1] (d) (i) The gradient of the line of best fit gives the volume of hydrogen gas produced per coulomb. Use the graph to determine the gradient of the line of best fit. State the co-ordinates of both points you used in your calculation. co-ordinates 1co-ordinates 2gradient =cm3 C1 [2] (ii) Calculate the number of moles of hydrogen gas produced per coulomb. If you were unable to obtain an answer for (d)(i), you may use the value 0.148 cm3 C1, but this is not the correct answer. [The molar volume of gas = 24.0 dm3 at room temperature and pressure.] (iii) Use your answer to (ii) and the half-equation for the production of H2(g) to calculate a numerical value for the Faraday constant (the charge of 1 mole of electrons).mol C1 [1] 2H+(aq) + 2e H2(g)C mol1 [1]UCLES 2017 9701/53/O/N/17<br /> 11 (e) (i) The graph below shows the relationship between volume of H2(g) produced at the cathode and time, in a similar experiment. Draw a line on the graph to show the relationship between volume of O2(g) produced at the anode and time in this experiment. PMT volume of gas produced / cm3 20.0 16.0 12.0 8.0 4.0 0.0 H2(g) 50 100 150 time / s 200 250 300 [1] (ii) Suggest why the volume of O2(g) measured in this experiment might be less than that shown by your drawn line. Assume that no gas is lost from leaks.[1] (f) In these experiments, the pressure of the gas inside the burette is assumed to be atmospheric pressure, Patm. However, the presence of water vapour and the mass of the solution in the burette change the pressure of the gas to Pnew. The expression below shows the relationship between Pnew and Patm. Pnew = Patm2.81(9.81height of solution in burette) (i) Use the expression to sketch a graph on the axes below to show the relationship between Pnew and the height of solution in the burette. Pnew height of solutionUCLES 2017 9701/53/O/N/17 [1] [Turn over<br /> (ii) State how Pnew changes the value of the Faraday constant calculated at Patm in (d)(iii). 12 PMT Explain your answer.[1] (g) A students teacher suggested it would be cheaper to use copper rather than platinum electrodes in the electrolysis of dilute sulfuric acid. half-equation 2H+(aq) + 2e Cu2+(aq) + 2e H2(g) Cu(s) 1 2O2(g) + 2H+(aq) + 2e H2O(l) E o / V 0.00 +0.34 +1.23 Using the information in the table, suggest what effect, if any, the use of copper electrodes would have on the volume of gas produced at each electrode. Explain your answer. cathodeanode[3] [Total: 16] 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 2017 9701/53/O/N/17<br />

Show answer