Question

When SO₂ is passed through an acidified solution of K2Cr2O7, then chromium sulphate is formed. Change in the oxidation state of Cr is from.

• A. $+4$ to $+2$
• B. $+6$ to $+3$
• C. $+7$ to $+2$
• D. $+5$ to $+3$

Answer 1

• The correct option is A (+4 to +2)
  In an acidic medium Cr is reduced from +6 to +3 as:
• Cr₂​O₇​⁻²+14H⁺+6e⁻→2Cr⁺³+7H₂​O
• and SO₂​ is oxidised to SO₃​ as:
• SO₂​+H₂​O→SO_3​+2H⁺+2e⁻