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JEE MainChemistryd and f Block Elements

When sulphur dioxide gas is passed through an acidified aqueous solution of potassium dichromate, the orange solution turns green. The compound responsible for this green colour is:

Options

  1. ACr ₂( SO ₄)₃
  2. BCrSO ₄
  3. CCr ₂ O ₃
  4. DCrO ₂ Cl ₂

Correct answer

A. Cr ₂( SO ₄)₃

Step-by-step solution

When SO ₂ gas is passed through an acidified solution of K ₂ Cr ₂ O ₇ , the dichromate ion acts as a strong oxidising agent. It oxidises SO ₂ to sulphate ( SO ₄²⁻ ) and itself gets reduced to chromium(III) ions ( Cr ³⁺ ). The balanced chemical equation is: K ₂ Cr ₂ O ₇ + 3 SO ₂ + H ₂ SO ₄ K ₂ SO ₄ + Cr ₂( SO ₄)₃ + H ₂ O The formation of chromium(III) sulphate, Cr ₂( SO ₄)₃ , is responsible for the green colour of the resulting solution. Answer: Cr ₂( SO ₄)₃

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