CIE Nov 2017 v1 Paper 4 Q3

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(a) Define the term standard cell potential. PMT[2] (b) (i) Draw a fully labelled diagram of the experimental set-up you could use to measure the standard electrode potential of the Pb2+(aq) / Pb(s) electrode. Include the necessary chemicals. (ii) The E o for a Pb2+(aq) / Pb(s) electrode is0.13 V. Suggest how the E for this electrode would differ from its E o value if the concentration of Pb2+(aq) ions is reduced. Indicate this by placing a tick () in the appropriate box in the table. more negative no change less negative [4] Explain your answer.[2]UCLES 2017 9701/41/O/N/17<br /> PMT (c) Car batteries are made up of rechargeable lead-acid cells. Each cell consists of a negative electrode made of Pb metal and a positive electrode made of PbO2. The electrolyte is H2SO4(aq). When a lead-acid cell is in use, Pb2+ ions are precipitated out as PbSO4(s) at the negative electrode. Pb(s) + SO4 2(aq) PbSO4(s) + 2e (i) Calculate the mass of Pb that is converted to PbSO4 when a current of 0.40 A is delivered by the cell for 80 minutes. mass of Pb =g [2] (ii) Complete the half-equation for the reaction taking place at the positive electrode. PbO2(s) + SO4 2(aq) ++PbSO4(s) +[1] (d) The diagrams show how the voltage across two different cells changes with time when each cell is used to provide an electric current. lead-acid cell H2 / O2 fuel cell voltage / V voltage / V time / hours time / hours Suggest a reason why the voltage of the lead-acid cell changes after several hours,the voltage of the fuel cell remains constant.[2]UCLES 2017 9701/41/O/N/17 [Total: 13] [Turn over<br />

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