CBSE Class 12 · 2003 · Foreign · d and f Block ElementsShort Answer

Write balanced equations to represent what happens when:
i) acidified KMnO

_{4}

solution reacts with iron(II) ions
ii) pyrolusite is fused with KOH in the presence of air

Answer: (i) MnO₄⁻+5Fe²⁺+8H⁺→Mn²⁺+5Fe³⁺+4H₂O. (ii) 2MnO₂+4KOH+O₂→2K₂MnO₄+2H₂O (green manganate).

Solution

(i) Permanganate oxidises ferrous to ferric:

Mn O_{4}^{-} + 5F e^{2 +} + 8 H^{+} \to M n^{2 +} + 5F e^{3 +} + 4 H_{2} O

(ii) First step of KMnO

_{4}

manufacture — fusion of pyrolusite with alkali in air gives green potassium manganate:

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

CBSE Class 12 Board · 2003 · Foreign · Subjective