Q7 of 26 Page 1

When pyrolusite ore is fused with KOH in the presence of air, a green coloured compound (A) is obtained which undergoes disproportionation reaction in acidic medium to give a purple coloured compound (B):

A. Write the formulae of the compounds (A) and (B).


B. What happens when compound (B) is heated?


(A) The reaction that would be taking place is


2MnO2 + 4KOH + O2→ 2K2MnO4(A) + 2H2O and KMnO4 is formed later after (A) undergoes disproportionation reaction in an acidic medium because acidic medium provides oxidation of potassium manganate to potassium permanganate.


(B) Potassium permanganate(B) when heated up reduced to potassium manganate. Following is the reaction:


2KMnO4(purple colour)→ K2MnO4(green colour)+ MnO2 + O2


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