OCR A Jun 2010 Paper 5 Q4

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4 Electrochemical cells have been developed as a convenient and portable source of energy. 10 The essential components of any electrochemical cell are two redox systems, one providing electrons and the other accepting electrons. The tendency to lose or gain electrons can be quantified using values called standard electrode potentials. Standard electrode potentials for seven redox systems are shown in Table 4.1. You may need to use this information throughout this question. Table 4.1 redox system equation 2H+(aq) + 2e Fe3+(aq) + e H2(g) Fe2+(aq) SO4 2(aq) + 2H+(aq) + 2e Ag+(aq) + e Cl 2(aq) + 2e O2(g) + 4H+(aq) + 4e I2(aq) + 2e 2(aq) + H2O(l) SO3 Ag(s) 2Cl (aq) 2H2O(l) 2I(aq) E o / V +0.77 +0.17 +0.34 +1.36 +1.23 +0.54 (a) An electrochemical cell can be made based on redox systems 2 and 4. (i) Draw a labelled diagram to show how this cell can be set up in the laboratory. [3] (ii) State the charge carriers that transfer current through the wire,through the solution.[1] (iii) Write down the overall cell reaction.[1] (iv) Write down the cell potential. cell potentialV [1]OCR 2010<br />
 (b) Select from Table 4.1, 11 (i) a species which oxidises Fe2+(aq) to Fe3+(aq),[1] (ii) a species which reduces Fe3+(aq) to Fe2+(aq) but does not reduce Ag+(aq) to Ag(s).[1] (c) Fuel cells are a type of electrochemical cell being developed as a potential source of energy in the future. State one important difference between a fuel cell and a conventional electrochemical cell.Write the equation for the overall reaction that takes place in a hydrogen fuel cell.State two ways that hydrogen might be stored as a fuel for cars. Suggest why some people consider that the use of hydrogen as a fuel for cars consumes more energy than using fossil fuels such as petrol and diesel.[5] [Total: 13]OCR 2010 Turn over<br />

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