Sulphur dioxide forms an acidic solution, sulphurous acid, when dissolved in water i.e. it turns damp blue litmus paper red. The main use of sulphur dioxide is in the production of sulphuric acid by the Contact Process . The yield for the reaction is dependent on a number of factors such as temperature, pressure, ratio of reactants and the use of a catalyst.
Sulphur dioxide is produced by car exhaust engines as well as sulphuric acid plants.
When the gas reaches the cloud layer in the atmosphere it dissolves in the water droplets present there and later falls to earth as what is known as acid rain. Therefore a filtration step is needed. Therefore titration is needed in this reaction to ensure that equal amounts of both the acid and the base react with one another.