Question

Give the characteristic tests for the following gases:

(a) CO₂
(b) SO₂
(c) O₂

Answer 1

The characteristic test:

(a) Carbon dioxide (CO₂) gas turns lime water milky when passed through it due to the formation of insoluble calcium carbonate.

(b) Sulphur dioxide (SO₂) gas when passed through acidic potassium permanganate solution (purple in colour) turns it colourless because SO₂ is a strong reducing agent

or Sulphur dioxide gas when passed through acidic dichromate solution (orange in colour) turns it to green because sulphur dioxide is a strong reducing agent.

(c) The evolution of oxygen (O₂) gas during a reaction can be confirmed by bringing a burning candle near the mouth of the test tube containing the reaction mixture. The intensity of the flame increases because oxygen supports burning.