Question:
A solution of KMnO4 on reduction yields either colourless solution or a brown precipitate or a green solution depending on the pH of the solution. What different stages of the reduction do these represent and how are they carried out?
Solution:
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- → MnO42-
(green)
In a neutral medium, permanganate changes to manganese dioxide which is a brown precipitate,
MnO4-+ 2H2O + 3e-→ MnO2 + 4OH-
(brown)
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