Sulphur Dioxide preparation properties and uses

Preparation of Sulphur Dioxide

1. In the laboratory, sulphur dioxide is prepared by the reaction of metallic sulphite or a metallic bisulphite with dilute acid. For example, a reaction between the dilute sulphuric acid and sodium sulphite will result in the formation of SO₂.

Na₂SO₃ + H₂SO₄ → Na₂SO₄ + H₂O + SO₂

2. Commercially it is obtained as a by-product released from the roasting of sulphide ores. The gas obtained is dried, liquefied and then stored in steel cylinders.

4FeS₂ (s) + 11 O₂ (g) →2Fe₂O₃ (s) + 8SO₂ (g)

Properties of Sulphur Dioxide

• It is a colourless gas with a rotten egg odour. It is highly soluble in water.
• It liquefies easily.
• SO₂ dissolves in water to form sulphurous acid due to which it possesses an acidic character.

H₂O + SO₂ → H₂SO₃

• It does not support combustion nor is it combustible.
• SO₂ is a strong oxidizing agent.

2H₂S + SO₂ → 3S + 2H₂O

• It also acts as a reducing agent.

SO₂ + 2H₂O → H₂SO₄ + 2H

Uses of Sulphur Dioxide

• In the food industries, as a food preservative.
• It acts as a bleaching agent to remove the excess chlorine and as a disinfectant.
• In cold storage plant, it acts as a refrigerant.
• It is used as a reagent and a solvent in the laboratory.