CIE Nov 2016 v3 Paper 4 Q4

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(a) Cobalt is a transition element that forms complex ions with oxidation states +2 and +3. PMT Explain what is meant by the term transition element.[1] (b) The following scheme shows some reactions of [Co(H2O)6]2+. OH(aq) [Co(H2O)6]2+ excess Cl (aq) excess NH3(aq) precipitate A solution of B solution of C (i) State the formula of each of the following. ABC(ii) State the colour of the following solutions. [Co(H2O)6]2+solution of Bsolution of C(c) Define the term standard electrode potential. [2] [2][2]UCLES 2016 9701/43/O/N/16<br /> PMT (d) An electrochemical cell was set up to measure the standard electrode potential, made of a Co2+ / Co half-cell and a Fe3+ / Fe2+ half-cell. , of a cell (i) Complete the table with the substance used to make the electrode in each of these half-cells. electrode half-cell Co2+ / Co Fe3+ / Fe2+ (ii) Write the equation for the overall cell reaction.[1] (iii) Use the Data Booklet to calculate the [1] =V [1] (e) The electrochemical cell in (d) was set up again but this time the concentration of Co2+(aq) was 0.050 mol dm3. The Nernst equation can be used to calculate the value of an electrode potential at different concentrations. E = E o + (0.059 / z) log [Co2+(aq)] Nernst equation (i) Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+ / Co half-cell in this experiment. E for Co2+ / Co =V [1] (ii) Suggest how this change will affect the overall cell potential, Ecell, compared to (d)(iii). Circle your answer. less positive no change more positive in [1] (f) Iron(III) ions can oxidise vanadium metal. Construct an equation for the reaction of an excess of iron(III) ions with vanadium metal. Use of the Data Booklet will be helpful.[2]UCLES 2016 9701/43/O/N/16 [Total: 14] [Turn over<br />

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