A solution of KMnO4 on reduction yields either acolourless 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?

Question

Philoid · Accepted Answer

In acidic medium, permanganate changes to manganous ion which is colourless.

MnO₄^-+8H⁺ + 5e^-→ Mn²⁺ + 4H₂O

^(colourless)

In alkaline medium, permanganate changes to manganate, which is a green solution

MnO₄^-+ e^- → MnO₄^2-

^(green)

In neutral medium, permanganate changes to manganese dioxide which is a brown precipitate,

MnO₄^-+ 2H₂O + 3e^-→ MnO₂ + 4OH^-

^(brown)