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Questions
Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with SO2? Write the ionic equation for the reaction.
Indicate the steps in the preparation of KMnO4 from pyrolusite ore.
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Solution 1
Potassium permanganate can be made by the following methods:
It is produced industrially by the electrolytic oxidation of manganate (VI), followed by the alkaline oxidative fusion of MnO2.
\[\ce{MnO2 ->[Fused with KOH, oxidised with air or KNO3] \underset{manganate ion}{MnO^2-_4}}\]
\[\ce{\underset{manganate}{MnO^2-_4} ->[Electrolytic oxidation in alkaline solution] \underset{permanganate ion}{MnO^-_4}}\]
The chemical reactions of acidic potassium permanganate are as follows:
\[\ce{2MnO^-4 + 2H2O + 5SO2 -> 2Mn^2+ + 4H^+ + 5SO^2-_4}\]
Solution 2
\[\ce{2MnO2 + 4KOH + O2 ->[\Delta] 2K2MnO4 + 2H2O}\]
\[\ce{3MnO^2-_4 + 4H+ -> 2MnO^-_4 + MnO2 + 2H2O}\]
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