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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.
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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.
\[\ce{2MnO2 + 4KOH + O2 -> 2K2MnO4 + 2H2O}\]
\[\ce{3MnO^{2-}_4 + 4H^+ -> 2MnO^-_4 + MnO2 + 2H2O}\]
In an acidic medium of dilute sulphuric acid, KMnO4 acts as a strong oxidising agent, and it reacts as:
\[\ce{MnO^-_4 + 8H^+ + 5e- -> Mn^2+ + 4H2O}\]
RELATED QUESTIONS
When chromite ore FeCr2O4 is fused with NaOH in presence of air, a yellow-coloured compound (A) is obtained, which on acidification with dilute sulphuric acid gives a compound (B). Compound (B) on reaction with KCl forms an orange coloured crystalline compound (C).
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Indicate the steps in the preparation of \[\ce{K2Cr2O7}\] from chromite ore.
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