Question

A solution of KMnO4 on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution.

Answer 1

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A solution of KMnO4 on reduction yields either a colourless solution or a brown precipitate or a green solution depending on pH of the solution. What different stages of the reduction do these represent and how are they carried out ?

ANSWER

Oxidising behaviour of KMnO₄ depends on pH of the solution

         In acidic medium (pH < 7)

                   MnO₄⁻ + 8H⁻ + 5e⁻ -------> Mn²⁺(colourless) + 4H₂O

         In alkaline medium (pH > 7)

                   MnO₄⁻ + e⁻ ------> MnO₄²⁻ (Green)

         In neutral medium (pH = 7)

                   MnO₄⁻ + 2H₂O + 3e⁻ -----> MnO₂( Brown precipitate) + 4OH⁻

Hope it helps you !!