Chemistry - Redox Reactions Question with Solution | TestHub
When ammonium vanadate is heated with oxalic acid solution, a substance Z is formed. A sample of Z was treated with KMnO₄ solution in hot acidic solution. The resulting liquid was reduced with SO₂, the excess SO₂ boiled off and the liquid again titrated with same KMnO₄. The ratio of the volumes of KMnO₄ used in the two titrations was 5:1. What is the oxidation state of vanadium in substance Z? Given than KMnO₄ oxidize all oxidation state of vanadium to vanadium (+5) and SO₂ reduces V (+5) to V (+4).
Answer:
Solution:
Per V atom in Z (O.S. = x, with b oxalate groups): first titration takes 2b e⁻ for the oxalates (C₂O₄²⁻ 2CO₂) plus (5-x) e⁻ for V(x +5). After SO₂ reduction to V(+4), the second titration takes 1 e⁻ (V +4 +5). Ratio: 2b + 5 - x = 5. For the vanadyl oxalate Z, b = 2, giving x = 4. Check: 4 + 1 = 5 : 1. Ans: 4.
