The reactions of chromium ions are illustrated below.
$[\text{Cr(H}_2\text{O)}_6]^{2+}(aq) \xrightarrow[\text{metal} + \text{H}_2\text{SO}_4]{\text{reaction 1}} [\text{Cr(H}_2\text{O)}_6]^{3+}(aq) \xrightarrow{\text{reaction 2}} \text{Cr}_2\text{O}_7^{2-}(aq)$
$\text{Cr}_2\text{O}_7^{2-}(aq) \xrightleftharpoons[\text{OH}^- (aq)]{\text{H}_3\text{O}^+ (aq)} \text{CrO}_4^{2-}(aq)$
(a(i))[1]
Use the Data Booklet to propose a suitable metal for reaction 1.
(a(ii))[2]
Use $E^\circ$ values to justify your answer to (i) by finding the $E^\circ_{\text{cell}}$.
(b)[2]
A student proposed that reaction 2 could be done using acidified hydrogen peroxide solution. Use the Data Booklet to show whether this reaction is feasible or not.
(c)[2]
Explain, using oxidation numbers, whether reaction 3 is a redox reaction or not.
(d)[3]
The student used an acidified solution of $\text{Cr}_2\text{O}_7^{2-}(aq)$ to electroplate a steel box with chromium metal. Calculate how long it would take for a current of $0.125\,\text{A}$ to deposit $0.0312\,\text{g}$ of chromium metal.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Any metal having $E^\circ < -0.41\ \text{V}$ e.g. Fe, Mn, Zn, Mg, Cr, Al” …