Cobalt is a transition element that forms complex ions with oxidation states $+2$ and $+3$. Explain what the term transition element means.
The reaction scheme below shows several 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 these solutions: $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$, solution B, solution C.
Define what is meant by standard electrode potential.
An electrochemical cell was assembled to find 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 down the equation for the overall cell reaction.
Use the Data Booklet to find the value of $E^\circ_{\text{cell}}$.
The Nernst equation can be used to find an electrode potential when the concentrations are different from the standard ones. $E = E^\circ + \frac{0.059}{z}\log[\text{Co}^{2+}(aq)]$ Use the Data Booklet and the Nernst equation to work out 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 one: 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. The Data Booklet may help.