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ICSE Class 9 Chemistry Question 1 of 31

Atmospheric Pollution — Question 8

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Question 8

Give balanced equations for the formation of sulphuric acid in acid rain, when a fossil fuel is burnt in an electric power station.

Answer
  1. When a fossil fuel is burnt in an electric power station sulphur dioxide is formed:
    S + O2 ⟶ SO2
  2. Sulphur dioxide reacts with water vapour to form sulphurous acid
    H2O + SO2 ⟶ H2SO3 [aq.]
  3. Sulphur dioxide can also be oxidized to sulphur trioxide [SO3]
    2SO2 + O2 ⟶ 2SO3
    [The reaction is catalyzed by dust particles and water droplets].
  4. Sulphur trioxide reacts with water vapour in air forming sulphuric acid
    H2O + SO3 ⟶ H2SO4 [aq.]

Thus, the acidity of rain is due to reaction of oxides of sulphur with water vapour forming dilute acids.