Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with (i) iron (II) ions (ii) `SO_(2)` and (iii) oxalic acid ? Write the ionic equations.

Explanation

Preparation of `KMnO_(4)` Potassium permanganate is prepared by the fusion of `MnO_(2)` with an alkali metal hydroxide and an oxidising agent like `KNO_(3)`. It forms dark green, `K_(2)MnO_(4)` which disproportionates in a neutral or acidic solution to give permanganate.
i) `2MnO_(2)+4KOH+O_(2) overset(KNO_(3))rarr2K_(2)MnO_(4)+2H_(2)O`
ii) `3MnO_(4)^(2-) +4H^(+) rarr 2MnO_(4)^(-) + MnO_(2)^(-) +MnO_(2) +2H_(2)O" or "3K_(2)MnO_(4)+2H_(2)SO_(4) rarr underset("Potassium permanganate")(2KMnO_(4)+2K_(2)SO_(4)+MnO_(2)+2H_(2)O)`
Reactions of `KMnO_(4)` in acidic medium
`MnO_(4)^(-) + 8H^(+) +5e^(-) rarr Mn^(2+) +4H_(2)O" -(i)"`
i) Iron (II) ions Ferrous is oxidised to ferric.
`[Fe^(2+) rarr Fe^(3+)+e^(-)]xx5" -(ii)"`
ii) `SO_(2)` : It is oxidised to `SO_(4)^(2-)` by acidified `KMnO_(4)`.
`SO_(2)+2H_(2)O rarr SO_(4)^(2-) +4H^(+) + 2e^(-)" -(iii)"`
From equation (i) and (iii)
`5SO_(2)+2MnO_(4)^(-) +2H_(2)O rarr 2Mn^(2+) +4H^(+) +5SO_(4)^(2-)`
Oxalic acid : `C_(2)O_(4)^(2-) rarr 2CO_(2)+2e^(-)" -(iv)"`
From equation (i) and (iv)
`5C_(2)O_(4)^(2-) +2MnO_(4)^(-) +16H^(+) rarr 2Mn^(2+) +8H_(2)O+10 CO_(2)`