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JEE MainChemistryd and f Block Elements

In a faintly alkaline medium, potassium permanganate ( KMnO ₄ ) quantitatively oxidises thiosulphate ions ( S ₂ O ₃²⁻ ). The number of moles of KMnO ₄ required to completely oxidise 1 mole of thiosulphate ion is

Options

  1. A8 3
  2. B8 5
  3. C2 3
  4. D1 3

Correct answer

A. 8 3

Step-by-step solution

In a faintly alkaline medium, KMnO ₄ is reduced to MnO ₂ and S ₂ O ₃²⁻ is oxidised to SO ₄²⁻ . For the reduction half-reaction ( KMnO ₄ MnO ₂ ): The oxidation state of Mn changes from +7 to +4 . The n -factor for KMnO ₄ is 3 . For the oxidation half-reaction ( S ₂ O ₃²⁻ 2 SO ₄²⁻ ): The average oxidation state of S in S ₂ O ₃²⁻ is +2 . The oxidation state of S in SO ₄²⁻ is +6 . The change in oxidation state per sulphur atom is +6 - (+2) = 4 . Since there are two sulphur atoms in one thiosulphate ion, the n -factor f

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