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How will you prepare potassium permanganate from pyrolusite ore? |
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Answer» Solution :Potassium permanganate is prepared from pyrolusite (MnO,) ore. The preparation involves the FOLLOWING steps. (i) Conversion of `MnO_(2)` to potassium manganate: Powdered ore is fused with KOH in the presence of air or oxidising agents like `KNO_(3)` . A green coloured potassium manganate is formed. `2MnO_(2)+ 2KOH+ O_(2)to underset(underset("(Green)")("Potassium manganate"))(K_(2)MnO_(4))+ 2H_(2)O` (ii) Oxidation of potassium manganate to potassium permanganate: Potassium manganate can be oxidised in two ways, either by chemical oxidation or electrolytic oxidation (iii) Chemical oxidation: In this method potassium manganate is treated with ozone (`O_(3)`) or chlorine to get potassium permanganate, `MnO_(4)^(2-)+ O_(3)+ H_(2)O to 2MnO_(4)^(-)+ 2OH^(-)+ O_(2)` `2MnO_(4)^(2-)+ CI_(2) to 2MnO_(4)^(-) + 2CI^(-)` (iv) Electrolytic oxidation: In this method aqueous solution of potassium manganate is electrolyzed in the presence of little ALKALI. `K_(2)MnO_(4) hArr 2K^(+)+MnO_(4)^(2-)` `H_(2)O hArr H^(+)+OH^(-)` Manganate ions are converted into permanganate ions at anode. `underset("(Green)")(MnO_(4)^(2-)) hArr underset("(purple)")(MnO_(4)^(-)) + e^(-)` `H_(2)` is liberated at the cathode. `2H^(+)+ 2e^(-) to H_(2)uarr` The purple coloured solution is CONCENTRATED by evaporation and FORMS crystals of potassium permanganate on cooling. |
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