Question

Write the preparation of the following :

(i) Na₂Cr₂O₇ from Na₂CrO₄

(ii) K₂MnO₄ from MnO₂

Answer 1

(i) Na₂Cr₂O₇ can be obtained from Na₂CrO₄ upon reaction with sulphuric acid.

\(2Na_2CrO_4 + H_2SO_4 \rightarrow Na_2Cr_2O_7 + Na_2SO_4 + H_2O\) 

(ii) K₂MnO₄ is prepared from MnO₂ by alkaline oxidative fusion with KOH in presence of oxidising agent such as air.

\(2MnO_2 + 4KOH + O_2 \rightarrow 2K_2MnO_4+2H_2O\)