Fill in the electronic configurations for a $\text{Co}^{2+}$ ion and a $\text{Co}^{3+}$ ion. $\text{Co}^{2+} = [\text{Ar}]\ \ldots$ ; $\text{Co}^{3+} = [\text{Ar}]\ \ldots$
Explain why transition elements are able to form complex ions.
An excess of concentrated $\text{HCl}$ is added to a solution containing $[\text{Co(H}_2\text{O)}_6]^{2+}$. State the colour change that is seen and the state of the cobalt-containing product. The colour changes from __________ to __________. The state of the cobalt-containing product is __________.
Write an equation for the reaction taking place in (a)(iii).
Name the reaction type in (a)(iii).
Write an equation for the reaction that happens when an excess of $\text{NaOH(aq)}$ is added to a solution containing $[\text{Co(H}_2\text{O)}_6]^{2+}$.
Cobalt metal can be oxidised by acidified $\text{K}_2\text{Cr}_2\text{O}_7$. The relevant half-equations, together with their $E^{\ominus}$ values, are shown.\n\n$\text{Co}^{2+} + 2e^- \rightleftharpoons \text{Co}\qquad E^{\ominus} = -0.28\,\text{V}$\n\n$\text{Cr}_2\text{O}_7^{2-} + 14\text{H}^+ + 6e^- \rightleftharpoons 2\text{Cr}^{3+} + 7\text{H}_2\text{O}\qquad E^{\ominus} = +1.33\,\text{V}$\n\nA $\text{Co}^{2+}/\text{Co}$ electrode is made in which $[\text{Co}^{2+}]$ is $0.020\,\text{mol dm}^{-3}$ at $298\,\text{K}$.\n\nUse the Nernst equation to show that the $E$ value for this $\text{Co}^{2+}/\text{Co}$ electrode is $-0.33\,\text{V}$.
An electrochemical cell is set up using the $\text{Co}^{2+}/\text{Co}$ electrode described in b(i) together with a $\text{Cr}_2\text{O}_7^{2-}/\text{Cr}^{3+}$ electrode under standard conditions throughout.\n\nCalculate the value of $E_{\text{cell}}$.
A current is drawn from the electrochemical cell described in b(ii).\n\nWrite an equation for the reaction occurring in the cell.
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).\n\nThe ............... electrode is the negative electrode.\n\nElectrons flow from the ............... electrode to the ............... electrode.
A molten $\text{Co}^{2+}$ salt is electrolysed with a current of $0.500\,\text{A}$.\n\n$0.547\,\text{g}$ of cobalt metal is deposited at the cathode. Under the conditions used, no other reduction process takes place at the cathode.\n\nCalculate the time in minutes for which the current must flow to produce this mass of cobalt.\n\nGive your answer to three significant figures.