Question

- i) A dark green solid compound (A) is prepared by fusion of MnO2 with
an alkali metal hydroxide and an oxygen. It disproportionate in a neutral
or acidic solution to give dark purple solid (B). Identify A and B. Write the
chemical equation involved in it.
linho folla​

Answer 1

Compound A is Potassium manganate and compound B is MnO₄⁻.

• Potassium manganate is prepared by reacting MnO₂ with an alkali metal hydroxide in the presence of an oxidizing agent. The reaction takes place as follows-

2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

K₂MnO₄ (Potassium manganate) is a dark green solid.

• Potassium manganate disproportionate in a neutral or acidic solution  to give dark purple solid of MnO₄⁻.

The reaction is as follows-

3MnO₄²⁻ + 4H⁺ (Acidic) → 2MnO₄⁻ + MnO₂ + 2H₂O