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       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

  1. It is a colourless and poisonous gas having a pungent smell.
  2. It is highly soluble in water.
  3. 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

  1. It is used in the manufacturing sulphuric acid.
  2. 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.
  3. It is used for bleaching wool pulp, straw, wool and silk.
  4. It is also used as a disinfectant.

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