141. Describe the preparation of potassium permanganate. How does the acidified permanganate solution reacts with (a) iron (II) ions (b) SO₂ and (c) oxalic acid ? Write the ionic equations for the reactions.

Preparation of KMnO₄ from pyrolusite ore (MnO₂) involves the following steps:
(i) Fusion of ore with alkali in presence of air : Pyrolusite ore is fused with alkali in the presence of air when potassium manganate is obtained as green mass.
2MnO₂ + 4KOH + O₂  → 2K₂MnO₄ + 2H₂O
(green mass)
The green mass is dissolved in water to obtain aqueous solution of potassium manganate. The insoluble impurities of sand and other metal oxides are removed by filtration.
(ii) Oxidation of manganate into permanganate : The aqueous solution of K₂MnO₄ is oxidised electrolytically or by using ozone or Cl₂ to obtain potassium permanganate. The process is carried out till green colour disappear and solution acquires distinct pink colour.$$\begin{gathered} {\mathrm{MnO}}_4^{2-} \to {\mathrm{MnO}}_4^{-} +{\mathrm{e}}^{-}(\mathrm{Oxidation} \mathrm{at} \mathrm{anode} ) \\ {\mathrm{H}}_2\mathrm{O} +{\mathrm{e}}^{-} \to 1/2{\mathrm{H}}_2 +(\mathrm{OH}{)}^{-} (\mathrm{Reduction} \mathrm{at} \mathrm{cathode}) \\ \mathrm{The} \mathrm{overall} \mathrm{reaction} \\ 2{\mathrm{K}}_2{\mathrm{MnO}}_4 +{\mathrm{Cl}}_2\to 2{\mathrm{KMnO}}_4 +2\mathrm{KCl} \\ green pink colour \\ { \\ }^{{{{{{{{{{{{}^{}}^{}}^{}}^{}}^{}}^{}}^{}}^{}}^{}}^{}}^{}} \end{gathered}$$
Potassium permanganate is crystallised out from the solution.
Oxidising Properties: It acts as a powerful oxidising agent in different media differently. In acidic medium, it oxidises iron(II) salts to iron(III) salts,
SO₂ to H₂SO₄ and oxalic acid to CO₂ and H₂O.
(a)    It oxidises iron(II) salt to iron(III) salts.
2MnO₄^2–+ 16H⁺+ 10Fe²⁺ → 2Mn²⁺ + 8H₂O + 10Fe³⁺
(b)    It oxidised sulphur dioxide to sulphuric acid.
2MnO₄^– + 5SO₂ + 2H₂O → 5SO₄^2– + 2Mn²⁺ 4H⁺
(c)    It oxidises oxalic acid to CO₂ and H₂O
2MnO₄^– + 16H⁺ + 5C₂O₄² → 2Mn²⁺ + 8H₂O + 10CO₂