# 2 8 970151mj18 ucles 2018 c the results the student

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8 9701/51/M/J/18 © UCLES 2018 (c) The results the student obtained are shown in the table. To calculate the concentration of C 6 H 5 N 2 + (aq) the student used the following equation. [C 6 H 5 N 2 + (aq)] = 0.0150 × (1 – V V final ) V = volume of N 2 (g) recorded at a specified time. V final = final volume of N 2 (g) at complete decomposition of C 6 H 5 N 2 + . V final is 72 cm 3 . Complete columns C and D to three significant figures. You may use the space below for any working. A B C D time / minutes volume of N 2 (g), V / cm 3 V V final [C 6 H 5 N 2 + (aq)] / mol dm –3 0.0 0 0.000 0.0150 2.0 9 0.125 0.0150 × (1 – 0.125) = 0.0131 4.0 17 6.0 24 8.0 30 10.0 35 12.0 40 14.0 44 16.0 48 [2]
9 9701/51/M/J/18 © UCLES 2018 [Turn over (d) Plot a graph on the grid to show the relationship between [C 6 H 5 N 2 + (aq)] and time. Use a cross ( × ) to plot each data point. Draw a line of best fit. 0.0 0.0150 0.0140 0.0130 0.0120 0.0110 0.0100 0.0090 0.0080 0.0070 0.0060 0.0050 0.0040 2.0 4.0 6.0 8.0 time / minutes 10.0 12.0 14.0 16.0 [C 6 H 5 N 2 + (aq)] / mol dm –3 [2]
10 9701/51/M/J/18 © UCLES 2018 (e) Draw a tangent at time = 0.0 on your graph and use the tangent to determine the initial rate of reaction. State the units of the initial rate of reaction. State the co-ordinates of both points you used in your calculation. co-ordinates 1 ................................................ co-ordinates 2 ................................................. initial rate of reaction = .............................. units = .............................. [4] (f) Use your graph to complete the table and calculate the values of two half-lives. For the first half-life, concentrations have been chosen for you. concentration 1 time 1 concentration 2 time 2 t 1 2 0.0120 ................ 0.0060 ................ ................ ....................... ................ ....................... ................ ................ [3] (g) State and explain what the values of the two half-lives suggest about the order of reaction with respect to [C 6 H 5 N 2 + (aq)]. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 18]
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12 9701/51/M/J/18 © UCLES 2018 BLANK PAGE 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.

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• Fall '19
• Electrochemistry, University of Cambridge, electrode, Cathode, Michael Faraday, UCLES

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