Question

What happens when:
(I) The manganate ion undergoes disproportionation reaction in acidic medium?
(II) KMnO4 is heated?

Answer 1

(I) Disproportionation of Manganate Ion in Acidic Medium

The manganate ion (\({MnO_4^{2-}}\)) undergoes a disproportionation reaction in an acidic medium.

In this reaction:

• One \({MnO_4^{2-}}\) ion is oxidized to permanganate ion (\({MnO_4^-}\), purple)
• The other is reduced to \({Mn^{2+}}\) (colourless)

 

Reaction:

\[ 2{MnO_4^{2-}} + 4{H^+} \rightarrow {MnO_4^-} + {Mn^{2+}} + 2{H_2O} \]

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(II) Thermal Decomposition of Potassium Permanganate

When potassium permanganate (\({KMnO_4}\)) is heated, it decomposes to form potassium manganate (\({K_2MnO_4}\)) and oxygen gas.

Reaction:

\[ 2{KMnO_4} \xrightarrow{\text{heat}} {K_2MnO_4} + {O_2} \]

This is a decomposition reaction that releases oxygen and forms a green manganate salt.