CBSE Class 12 · 2006 · Delhi · d and f Block ElementsShort Answer

Write chemical equations for the reactions involved in the manufacture of potassium permanganate from pyrolusite ore.

Answer: 2MnO₂+4KOH+O₂→2K₂MnO₄+2H₂O; then anodic oxidation MnO₄²⁻→MnO₄⁻+e⁻ (or 3MnO₄²⁻+4H⁺→2MnO₄⁻+MnO₂+2H₂O).

Solution

Step 1 — fuse pyrolusite with KOH in air (or with an oxidant like KNO

_{3}

) to get green potassium manganate:

2Mn O_{2} + 4KOH + O_{2} Δ 2 K_{2} Mn O_{4} + 2 H_{2} O

Step 2 — oxidise manganate to purple permanganate, electrolytically at the anode:

Mn O_{4}^{2 -} \to Mn O_{4}^{-} + e^{-}

(or by disproportionation in acid:

3Mn O_{4}^{2 -} + 4 H^{+} \to 2Mn O_{4}^{-} + Mn O_{2} + 2 H_{2} O

CBSE Class 12 Board · 2006 · Delhi · Subjective