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8.16 Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with

(i) iron

Write the ionic equations for the reactions.    

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Potassium permanganate can be prepared from the fusion of pyrolusite ore(MnO_{2}) with an alkali metal hydroxide and an oxidising agent (like KNO_{3}). This gives dark green K_{2}MnO_{4}. It disproportionates in acidic or neutral medium to give permanganate.

\\2MnO_{2}+4KOH+O_{2}\rightarrow 2K_{2}MnO_{4}+2H_{2}O\\ 3MnO_{4}^{2-}+4H^{+}\rightarrow 2MnO_{4}^{-}+MnO_{2}+H_{2}O

(i)Acidified permanganate ion reacts with iron-

\\MnO_{4}^{-}+8H^{+}+5e^{-}\rightarrow Mn^{2+}+4H_{2}O\\ Fe^{2+}\rightarrow Fe^{3+}+e^{-}]\times 5
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MnO_{4}^{-}+5Fe^{2+}+8H^{+}\rightarrow Mn^{2+}+ 5Fe^{3+}+4H_{2}O\\

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manish

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