Cobalt is a transition element which forms compounds containing Co2+ and Co3+ ions. Cobalt(II) sulfate dissolves in water to form a solution containing the [Co(H2O)6]2+ complex ion.

1. (a)(i)Complete the electronic configurations of a Co2+ ion and a Co3+ ion. Co2+ = [Ar] Co3+ = [Ar][1]
2. (a)(ii)Explain why transition elements can form complex ions.[1]
3. (a)(iii)An excess of concentrated HCl is added to a solution containing [Co(H2O)6]2+. Describe the colour change observed and the state of the cobalt-containing product. The colour changes from to The state of the cobalt-containing product is[2]
4. (a)(iv)Write an equation for the reaction occurring in (a)(iii).[1]
5. (a)(v)Name the type of reaction occurring in (a)(iii).[1]
6. (a)(vi)Write an equation for the reaction that occurs when an excess of NaOH(aq) is added to a solution containing [Co(H2O)6]2+.[1]
7. (b)(i)Cobalt metal can be oxidised by acidified K2Cr2O7. The relevant half-equations, and their E° values, are shown. Co2+ + 2e– ⇌ Co E° = –0.28 V Cr2O72– + 14H+ + 6e– ⇌ 2Cr3+ + 7H2O E° = +1.33 V A Co2+/Co electrode is constructed in which [Co2+] is 0.020 mol dm–3 at 298 K. Use the Nernst equation to show that the E value for this Co2+/Co electrode is –0.33 V.[2]
8. (b)(ii)An electrochemical cell is constructed using the Co2+/Co electrode described in (b)(i) and a Cr2O72–/Cr3+ electrode in which all conditions are standard. Calculate the value of Ecell. Ecell =[1]
9. (b)(iii)A current is drawn from the electrochemical cell described in (b)(ii). Write an equation for the reaction taking place in the cell.[1]
10. (b)(iv)Complete the sentences to identify the negative electrode and the direction of electron flow when a current is drawn from the cell described in (b)(ii). The electrode is the negative electrode. Electrons flow from the electrode to the electrode.[1]
11. (c)A molten Co2+ salt is electrolysed using a current of 0.500 A. 0.547 g of cobalt metal forms at the cathode. Under the conditions used no other reduction reaction occurs at the cathode. Calculate the time in minutes for which the current flows to produce this mass of cobalt. Give your answer to three significant figures. time = min[3]