Question

Acidified K₂Cr₂O₇ solution turns green when Na₂SO₃ is added to it. This is due to the formation of ______.

Options

• \[\ce{CrO^{2-}_4}\]

• Cr₂(SO₃)₃

• CrSO₄

• Cr₂(SO₄)₃

Answer 1

Acidified K₂Cr₂O₇ solution turns green when Na₂SO₃ is added to it. This is due to the formation of Cr₂(SO₄)₃.

Explanation:

Potassium dichromate(K₂Cr₂O₇) is orange in colour. When sodium sulphite (Na₂SO₃)is added to its acidified solution, a redox reaction occurs. In this reaction, dichromate ion \[\ce{(Cr2O^{2-}_7)}\] is reduced to Cr³⁺. \[\ce{SO^{2-}_3}\] is oxidised to \[\ce{SO^{2-}_4}\]. The Cr³⁺ forms chromium (III) sulphate, i.e., Cr₂(SO₄)₃, which is green in colour.