8.16 Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron(II) ions (ii) SO2 and (iii) oxalic acid? Write the ionic equations for the reactions.

Step 1:

Preparation of 
potassium permanganate is as follows:

Potassium permanganate is prepared by fusion of MnO2 with an alkali metal hydroxide and an oxidizing agent like KNO3 . This produces the dark green K2MnO4 which disproportionates in a neutral or acidic solution to give permanganate. 

The reactions are as follows:

2MnO2 + 4KOH + O2 → 2K2MnO4 + 2H2
3MnO42– + 4H+ → 2MnO4 + MnO2 + 2H2O

Step 2:

The reaction of acidified permanganate solution with (i) iron(II) ions (ii) SO2 and (iii) oxalic acid are as follows:

(i) Fe2+ ion (green) is converted to Fe3+ (yellow) when acidified permanganate solution reacts with Fe2+. The reaction is as follows:

5Fe2+ + MnO4 + 8H+ → Mn2+ + 4H2O + 5Fe3+ 

(ii) The reaction between SO2 and acidified permanganate solution is as follows:

\(\begin{aligned} 2 \mathrm{MnO}_{4}^{-}+2 \mathrm{H}_{2} \mathrm{O} +5 \mathrm{SO}_{2} \rightarrow \mathrm{SO}_{4}^{2-} +2 \mathrm{Mn}^{2+} &+2 \mathrm{H}_{2} \mathrm{SO}_{4} \end{aligned}\)

Acidified permanganate solution oxidizes oxalates to carbon dioxide. The reaction is as follows:

\(2 \mathrm{MnO}_{4}^{-}+16 \mathrm{H}^{+}+5 \mathrm{C}_{2} \mathrm{O}_{4}^{2-} \rightarrow 2 \mathrm{Mn}^{2+}+8 \mathrm{H}_{2} \mathrm{O}+10 \mathrm{CO}_{2}\)