OCR A Jun 2014 Paper 5 Q7

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7 Electrochemical cells contain two redox systems, one providing electrons and the other accepting electrons. The tendency to lose or gain electrons is measured using values called standard electrode potentials. 16 (a) Define the term standard electrode potential. Include all standard conditions in your answer.[2] (b) The table below shows two redox systems and their standard electrode potentials, E . Redox system Cu2+(aq) + 2e Ag+(aq) + e Cu(s) Ag(s) E / V +0.34 +0.80 A standard Cu2+(aq) / Cu(s) half-cell is connected to a standard Ag+(aq) / Ag(s) half-cell. The potential of the cell is measured. Water is then added to the Cu2+(aq) / Cu(s) half-cell. This changes the position of equilibrium in the half-cell. The cell potential increases. (i) Write down the equation for the overall cell reaction.[1] (ii) Explain, in terms of equilibrium, why the cell potential increases.[3]OCR 2014<br />
 (c) Hydrogen fuel cells are being developed for powering vehicles. 17 (i) State one advantage of using hydrogen as a fuel compared with conventional fuels.[1] (ii) In vehicles, hydrogen can be stored on the surface of a solid material or within a solid material. State one other way that hydrogen can be stored as a fuel for vehicles.[1] (d) Aluminiumoxygen cells are being investigated for powering vehicles. The reactions at each electrode are shown below. Al (s) + 4OH(aq) O2(g) + 2H2O(l) + 4e (aq) + 3e Al (OH)4 4OH(aq) (i) The standard electrode potential for the O2 / OH redox system is +0.40 V. The standard cell potential of an aluminiumoxygen cell is 2.71 V. What is the standard electrode potential of the aluminium redox system in this cell? standard electrode potential =V [1] (ii) Construct the overall cell equation for an aluminiumoxygen cell.OCR 2014 [2] [Total: 11] Turn over<br />

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