# Mass change of anode 0282 g mass change of cathode

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mass change of anode = – 0.282 g mass change of cathode = +0.217 g Suggest one reason why the mass gained at the cathode is not the same as the mass lost at the anode. Assume the student has recorded the mass changes correctly. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 12]
6 9701/51/M/J/18 © UCLES 2018 2 At temperatures above 5 ° C, the benzenediazonium ion, C 6 H 5 N 2 + , reacts with water as shown. C 6 H 5 N 2 + (aq) + H 2 O(l) C 6 H 5 OH(aq) + N 2 (g) + H + (aq) A student investigates this reaction by measuring the volume of nitrogen gas produced at regular time intervals. The diagram shows the experimental set-up used to investigate this reaction. C 6 H 5 N 2 + (aq) gas syringe conical flask (a) The student finds that the reaction is very slow, so decides to investigate the reaction at 30 ° C. Complete the diagram to show how the student could investigate this reaction at a constant 30 ° C. [2]
7 9701/51/M/J/18 © UCLES 2018 [Turn over (b) The student prepared a solution of C 6 H 5 N 2 + (aq) at 5 ° C. A 200.0 cm 3 sample of this solution was placed in a conical flask. The apparatus was allowed to equilibrate at 30 ° C. The gas syringe was then connected, a stop-clock was started and readings of time and gas volume were taken. When the decomposition of the C 6 H 5 N 2 + ion was complete (as shown by no more gas production) the final volume of N 2 (g) produced, V final , was 72 cm 3 . (i) Show by calculation that when the stop-clock was started the concentration of C 6 H 5 N 2 + (aq) was 0.0150 mol dm –3 . [The molar volume of gas under room conditions is 24.0 dm 3 .] concentration of C 6 H 5 N 2 + (aq) = .............................. mol dm –3 [2] (ii) The volume of nitrogen produced is proportional to the amount of C 6 H 5 N 2 + that reacts. As C 6 H 5 N 2 + reacts, its concentration in the solution falls. Using the axes shown, sketch a graph to show the change in volume of N 2 (g) produced with the change in concentration of C 6 H 5 N 2 + (aq). Label the axes [C 6 H 5 N 2 + (aq)] / mol dm –3 and volume of N 2 (g) / cm 3 , putting the independent variable on the x -axis. Include on the axes the maximum values for concentration and volume where the lines on the axes are shown. 0 0

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

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