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Question
Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with iron (II) ions? Write the ionic equation for the reaction.
Solution
Potassium permanganate is prepared by fusion of MnO2 with an alkali metal hydroxide and an oxidising agent like KNO3. This produces the dark green K2MnO4 which disproportionates in a neutral or acidic solution to give permanganate.
\[\ce{2MnO2 + 4KOH + O2 -> 2K2MnO4 + 2H2O}\]
\[\ce{3MnO^{2-}_4 + 4H^+ -> 2MnO^-_4 + MnO2 + 2H2O}\]
The chemical reactions of acidic potassium permanganate are as follows –
\[\ce{MnO^-_4 + 8H^+ + 5Fe^{2+} -> Mn^{2+} + 4H2O + 5Fe^{3+}}\]
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