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Give preparation of potassium permanganate |
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Answer» Solution :(i) Laboratory preparation: In a laboratory, `KMnO_(4)` can be PREPARED by oxidation of Mn(II) salts by peroxodisulphate `2Mn^(2+) + 5S_(2)O_(8)^(2-) + 8H_(2)O rarr 2MnO_(4)^(-) + 10SO_(4)^(2-) + 16H^(+)` (ii) Commercial preparation: Step-1 Conversion of `MnO_(2)` to potassium manganate. A dark coloured potassium manganate `(K_(2)MnO_(4))` is obtained when `MnO_(2)` is fused with an alkali metal hydroxide in presence of oxidizing agent such as `KnO_(3)`. `2MnO_(2) + 4KOH + O_(2) rarr underset(("Green"))(2K_(2)MnO_(4)) + 2H_(2)O` Step-2 Conversion of `K_(2)MnO_(4) " to " KMnO_(4)` (i) Potassium manganate disproportionates in a neutral or acidic medium to give potassium permanganate `3MnO_(4)^(2-) + 4H^(+) rarr underset(("dark purple"))(2MnO_(4)^(-)) + underset(("Brown ppt"))(MnO_(2) + 2H_(2)O)` The above reaction can also be carried out using a current of `CO_(2), Cl_(2)` OR `O_(3)`. (ii) Electrolytic method: This is the modern method of conversion of potassium manganate to potassium permanganate. It is known as electrolytic oxidation. `MnO_(4)^(-)` is obtained at anode. Anode: `underset(("Green"))(MnO_(4)^(2-)) underset("Oxidation")OVERSET("Electrolytic")rarr underset(("purple"))(MnO_(4)^(-)) + e^(-)` The purple solution of potassium permanganate is evaporated to dryness to get CRYSTALS of potassium permanganate |
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