CIE Jun 2014 v3 Paper 5 Q2

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An experiment was set up to investigate how the cell potential of a cell containing a metal, M, in contact with an aqueous solution of its ions, Mn+(aq) (where n = 1, 2 or 3), changed as Mn+(aq) was diluted. Since a standard hydrogen half-cell was not available, a standard half-cell consisting of silver in contact with a 1 mol dm3 solution of silver ions was used to connect to the half-cell with M in contact with Mn+(aq). PMT salt bridge metal M electrode Mn+(aq) ions silver electrode 1 mol dm3 Ag+(aq) ions The metal electrodes of the two half-cells were connected via a voltmeter, reading to two decimal places. This was used to measure the cell potential of the cell. The cell potential was measured for various concentrations of Mn+(aq) and the results obtained are shown in the table below. (a) Complete the third column of the table below. Give each answer to two decimal places. concentration of Mn+(aq) / mol dm3 cell potential / V log [Mn+(aq)] 5.00101 1.00101 4.00102 1.00102 5.00103 2.00103 8.00104 2.00104 0.94 0.96 0.97 0.99 1.00 1.01 1.02 1.04 [2]UCLES 2014 9701/53/M/J/14<br /> PMT (b) Plot a graph to show the relationship between log [Mn+(aq)] and the cell potential measured and draw the line of bestt. cell potential / V 1.04 1.03 1.02 1.01 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0.93 0.924.54.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0UCLES 2014 9701/53/M/J/14 [Turn over<br /> PMT (c) Are there any anomalous points on your graph? If so, circle those points. Give a reason for your answer.[2] (d) It is known that the cell potential of a cell, E, is related to the standard electrode potential, E o, by the equation: E = E o0.06 log [Mn+(aq)] (i) Use your graph to determine the charge, n, of the Mn+ ions. Draw appropriate lines on your graph to enable you to calculate its slope and show in the space below, how n was calculated. (ii) Use your graph to determine the standard electrode potential, E o, of the cell.[1] [3] (e) The standard electrode potential for silver is +0.80 V. Calculate the standard electrode potential for the metal, M. Use the data given on page 12 to suggest the identity of M.[1]UCLES 2014 9701/53/M/J/14<br /> PMT (f) Write an overall equation for the cell reaction which is taking place.[1] (g) The solutions contained in the two half-cells must be connected using a salt bridge. (i) Why is a salt bridge necessary?[1] (ii) Which (if any) of the following salts would be suitable to use in the salt bridge: potassium chloride, potassium nitrate, potassium sulfate? If you consider any to be unsuitable, explain why.[2] [Total: 15]UCLES 2014 9701/53/M/J/14 [Turn over<br />

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