Question

Indicate the steps in the preparation of K₂Cr₂O₇ from the chromite ore and KMnO₄ from pyrolusite ore.

Answer 1

Preparation of K₂Cr₂O₇

It takes place in three steps:

Conversion of chromite ore into sodium chromate

4FeCr₂O₄ + 4Na₂CO₃ + 7O₂  → Na₂CrO₄ + Fe₂O₃ + 8CO₂

Conversion of sodium chromate into sodium dichromate

2Na₂CrO₄ + 2H⁺ →  Na₂Cr₂O₇ + 2Na⁺ + H₂O

Conversion of sodium dichromate into potassium dichromate

Na₂Cr₂O₇ + 2KCl → K₂ Cr₂O₇ + 2NaCl

KMnO₄ from pyrolusite ore

The green mass can be extracted with water and then oxidized either electrolytically or by passing chlorine/ozone into the solution. Electrolytic oxidation