OCR A Jun 2016 Paper 5 Q6

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6 Redox reactions can be used to generate electrical energy from electrochemical cells. A student investigates the redox systems shown in Table 6.1 below. 14 Redox system Al 3+(aq) + 3e Cr3+(aq) + e V3+(aq) + e Cu2+(aq) + 2e Al (s) Cr2+(aq) V2+(aq) Cu(s) E o/ V 1.66 0.41 0.26 +0.34 Cr2O7 FeO4 2(aq) + 14H+(aq) + 6e 2(aq) + 8H+(aq) + 3e 2Cr3+(aq) + 7H2O(l) +1.33 Fe3+(aq) + 4H2O(l) +2.20 Table 6.1 (a) Define the term standard electrode potential. Include all standard conditions in your answer.[2] (b) The student sets up a standard cell based on redox systems 3 and 4. (i) Draw a labelled diagram to show how the student could have set up this cell to measure the standard cell potential. On your diagram,show the charge carriers in the circuit joining the two half cells label the signs of the electrodes. [5]OCR 2016<br />
 (ii) What is the standard cell potential of this cell? 15 (c) Explain what is meant by the terms oxidising agent and reducing agent. standard cell potential =V [1] Illustrate your answer by predicting reactions from redox systems 16 in which Cr3+(aq) behaves as an oxidising agent and as a reducing agent. Include overall equations and explain why you have made your predictions. State symbols are not required.[6]OCR 2016 [Total: 14] Turn over<br />

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