Question

A mixture of salts (Na₂SO₃ + K₂Cr₂O₇) in a test tube is treated with dil. H₂SO₄ and resulting gas is passed through lime water. Which of the following observations is correct about this test? 

(a) Solution in test tube becomes green and lime water turns milky. 

(b) Solution in test tube is colourless and lime water turns milky. 

(c) Solution in test tube becomes green and lime water remains clear. 

(d) Solution in test tube remains clear and lime water also remain clear.

Answer 1

Correct option (c)

Explanation:

Na₂SO₃ with dil. H₂SO₄ gives SO₂ gas which reacts with K₂Cr₂O₇ to give a green solution due to Cr₂(SO₄)₃. Since whole of the gas is consumed, the lime water will remain clear.

Na₂SO₃ + H₂SO₄ → Na₂SO₄ + SO₂ + H₂O 

K₂Cr₂O₇ + 3SO₂ + H₂SO₄→ K₂SO₄ + (green) Cr₂(SO₄)₃ + H₂O