How does permanganate ion behave in redox reactions?

1 Answer
anor277
Apr 25, 2017

Well, permanganate anion is generally reduced to (colourless) Mn^(2+) in acidic solution..........

Explanation:

MnO_4^(-) +8H^+ +5e^(-) rarr Mn^(2+) + 4H_2O(l)

Note that Mn^(2+) is almost colourless in aqueous solution; it is a d^5 system, for which electronic transition is spin forbidden. Very concentrated solutions are pale rose.

In basic solution, generally, permanganate is reduced to MnO_2(s), a 3 electron reduction:

MnO_4^(-) + 4H^+ +3e^(-) rarr MnO_2(s) + 2H_2O(l) (but BASIC conditions were specified, so we add 4xxHO^- to both sides.....

MnO_4^(-) + 2H_2O +3e^(-) rarr MnO_2(s) + 4HO^(-)

Of course you need the corresponding oxidation equation. But there is formal 5e^- transfer in acid, and 3e^- transfer in base.

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