Sulphur dioxide is a colourless gas which is present in the exhaust gases coming out of automobiles and factories. It is a poisonous gas having molecular formula SO2. It can cause inflammation of lungs when inhaled in the body. It is main source of air pollution.
Sulphur dioxide is highly soluble in water. It dissolves in rain water to form sulphuric acid and hence causes acid rain which is responsible for damaging historical buildings, bridges, metal works and plants.
Preparation of Sulphur Dioxide
In laboratory, sulphur dioxide is prepared by heating copper turnings with concentrated sulphuric acid.
Cu + 2H2SO4 CuSO4 + SO2 + 2H2O
Copper Sulphuric acid Copper sulphate Sulphur dioxide Water
Physical Properties of Sulphur Dioxide
- It is a colourless and poisonous gas having a pungent smell.
- It is highly soluble in water.
- It is heavier than air.
Chemical Properties of Sulphur Dioxide
1. Sulphur Dioxide is Acidic in Nature
Sulphur dioxide is acidic in nature because solution of sulphur dioxide in water turns blue litmus red.
2. Reaction with Lime Water
Sulphur dioxide turns lime water (calcium hydroxide) cloudy due to formation of calcium sulphite.
SO2 + Ca(OH)2 CaSO3 + H2O
Sulphur dioxide Calcium hydroxide Calcium sulphite Water
3. Reaction with Sodium Hydroxide
Sulphur dioxide produce sodium sulphite when passed through sodium hydroxide solution.
2NaOH + SO2 Na2SO3 + H2O
Sodium hydroxide Sulphur dioxide Sodium sulphite Water
4. Reaction with Oxygen
When sulphur dioxide is heated to 450°C with oxygen in the presence of vanadium oxide, sulphur trioxide is formed.
2SO2 + O2 2SO3
Sulphur dioxide Oxygen Sulphur trioxide
5. Reaction with Water
Sulphur dioxide dissolves in water to form sulphuric acid.
2SO2 + 2H2 O H2SO4 + 2[H]
Sulphur dioxide Sulphuric acid
Uses of Sulphur Dioxide
- It is used in the manufacturing sulphuric acid.
- It prevents the growth of bacteria. So, it is used as a preservative for the preservation of dry fruits, jams and lemon and orange squashes.
- It is used for bleaching wool pulp, straw, wool and silk.
- It is also used as a disinfectant.
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