JAMB Chemistry 2024 Paper

Concept:Sulphur(IV)oxide, $\mathrm{SO}_2$, acts as a reducing agent, while acidified tetraoxomanganate(VII), $\mathrm{MnO}_4^-$, acts as an oxidising agent.Explanation:When $\mathrm{SO}_2$ is passed into an acidified solution of $\mathrm{MnO}_4^-$, a redox reaction occurs.The purple $\mathrm{MnO}_4^-$ ion is reduced to colourless $\mathrm{Mn}^{2+}$ in acidic conditions.At the same time, $\mathrm{SO}_2$ is oxidised to sulphate, $\mathrm{SO}_4^{2-}$.The deep purple colour of tetraoxomanganate(VII) therefore disappears as the reaction proceeds.The final solution becomes colourless because $\mathrm{Mn}^{2+}$ ions do not absorb visible light strongly.Answer:C. purple to colourless