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Question:

In order to oxidise a mixture one mole of each of FeC₂O₄, Fe₂(C₂O₄)₃, FeSO₄ and Fe₂(SO₄)₃ in acidic medium, the number of moles of KMnO₄ required is:

2

1

3

1.5

Solution:

Correct option is B.
2Change in oxidation state for respective species:
Fe²⁺→Fe³⁺
C₂O₄²⁻→2CO₂ + 2e⁻
MnO₄⁻→Mn²⁺ + 5e⁻
Note: There will be no change in the oxidation state of Fe₂(SO₄)₃ as Fe is already in the highest oxidation state.
Using equivalence concept:
neq(KMnO₄)=neq[FeC₂O₄]+neq[Fe₂(C₂O₄)₃]+neq[FeSO₄]
n × 5 = 1 × 3 + 1 × 6 + 1 × 1 = 10
∴n = 2