Question

Write the balanced equation for the reaction between acidified KMnO₄ and FeSO₄ by oxidation number method.

Answer 1

\(\overset{+7}{KMnO_4 }+ \overset{+2}{Fe}SO_4+ H_2SO_4 \longrightarrow K_2SO_4 + \overset{+2}{Mn}SO_4 + \overset{+2}{Fe_2}(SO_4)_3 + H_2O\)

Increase in O.N. per FeSO₄ (from +2 to +3) = 1

Since one Fe₂(SO₄)₃ can only be derived from 2FeSO₄

\(\therefore\) Total increase in O.N. = 2

Decrease in O.N. per KMnO₄ (from +7 to +2) = 5

Hence multiply FeSO₄ by 5 and KMnO₄ by 2 so as to make total increase and decrease in O.N. the same

\(\therefore\) 2KMnO₄ + 10FeSO₄ + 8H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5Fe₂(SO₄)₃ + H₂O