Write out the electronic configurations for these ions. $\text{Cr}^{3+}: 1s^2 2s^2 2p^6 \ldots$ $\text{Mn}^{2+}: 1s^2 2s^2 2p^6 \ldots$
$\text{KMnO}_4$ and $\text{K}_2\text{Cr}_2\text{O}_7$ both act as oxidising agents, generally in acidic solution. Use the Data Booklet to explain why their oxidising power becomes greater as the $[\text{H}^+(aq)]$ in the solution increases.
What colour changes would you see when each of these oxidising agents is fully reduced? $\text{KMnO}_4$: from \ldots\ldots\ldots\ldots\ldots\ldots to \ldots\ldots\ldots\ldots\ldots\ldots $\text{K}_2\text{Cr}_2\text{O}_7$: from \ldots\ldots\ldots\ldots\ldots\ldots to \ldots\ldots\ldots\ldots\ldots\ldots
Manganese(IV) oxide, $\text{MnO}_2$, is a dark brown solid that does not dissolve in water or dilute acids. However, bubbling a stream of $\text{SO}_2(g)$ through a suspension of $\text{MnO}_2$ in water causes it to dissolve and form a colourless solution. Use the Data Booklet to propose an equation for this reaction, and explain how the oxidation states of manganese and sulfur change during the process.
The pH of the $\text{MnO}_2$ suspension is lowered. Explain what effect, if any, this would have on the extent of this reaction.
The principal manganese ore, pyrolusite, is mostly $\text{MnO}_2$. A $\text{SnCl}_2$ solution can be used, by the method given, to determine the percentage of $\text{MnO}_2$ in a pyrolusite sample. Use the Data Booklet to form an equation for the reaction between $\text{MnO}_2$ and $\text{Sn}^{2+}(aq)$ ions in acidic solution.
Calculate the percentage of $\text{MnO}_2$ in this pyrolusite sample by carrying out the following steps: • number of moles of $\text{MnO}_4^-$ used in the titration • number of moles of $\text{Sn}^{2+}$ this $\text{MnO}_4^-$ reacted with • number of moles of $\text{Sn}^{2+}$ that reacted with the $0.100\,\text{g}$ sample of pyrolusite • number of moles of $\text{MnO}_2$ in $0.100\,\text{g}$ pyrolusite. Use your equation in (i) • mass of $\text{MnO}_2$ in $0.100\,\text{g}$ pyrolusite • percentage of $\text{MnO}_2$ in pyrolusite