Cobalt is a transition element that forms complex ions with oxidation states $+2$ and $+3$. Explain what is meant by the term transition element.
The scheme below shows some reactions of $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$. State the formula of each of the following: A, B and C.
State the colour of each of the following solutions: $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$, solution of B, solution of C.
Define what is meant by standard electrode potential.
An electrochemical cell was assembled to determine the standard electrode potential, $E^{\circ}_{\text{cell}}$, of a cell made from a $\text{Co}^{2+}/\text{Co}$ half-cell and a $\text{Fe}^{3+}/\text{Fe}^{2+}$ half-cell. Complete the table with the material used for the electrode in each half-cell.
Write the equation for the reaction that occurs in the cell.
Use the Data Booklet to calculate $E^{\circ}_{\text{cell}}$.
The electrochemical cell in (d) was set up again, but this time the concentration of $\text{Co}^{2+}(aq)$ was $0.050\,\text{mol dm}^{-3}$. The Nernst equation can be used to calculate the value of an electrode potential at different concentrations. $E = E^{\circ} + (0.059/z)\log[\text{Co}^{2+}(aq)]$ Use the Data Booklet and the Nernst equation to calculate the value of $E$ for the $\text{Co}^{2+}/\text{Co}$ half-cell in this experiment.
Suggest how this change will alter the overall cell potential, $E_{\text{cell}}$, compared with $E^{\circ}_{\text{cell}}$ in (d)(iii). Circle your answer: less positive, no change, more positive.
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.