Question

What happens when sulphur dioxide is dissolved in water?

Answer 1

Hint :Sulphur comes in the Group $ 16 $ of the periodic table which is also known by the name of the group of chalcogens. Sulphur is a non-metal which exists as polyatomic molecule (S8).sulphur have capability to extend its oxidation number from $ \left( { + 4} \right) $ too $ \left( { + 6} \right) $ due to presence of vacant $ \left( d \right) $ orbitals.

Complete Step By Step Answer:
Sulphur has the tendency to react with oxygen to form sulphur dioxide $ \left( {S{O_2}} \right) $ which acts as a good reducing agent in the chemical reactions.
When solid sulphur is burnt in oxygen or air it produces sulphur dioxide along with a small amount of sulphur trioxide.
 $ {S_{\left( S \right)}} + {O_{2\left( g \right)}} \to S{O_{2\left( g \right)}} $
Sulphur dioxide from during the reaction is highly acidic in nature. Sulphur dioxide has the tendency to react with water hence, it is known as acidic oxide.
Sulphur dioxide gas is highly soluble in water and has a pungent smell.
Due to high solubility of sulphur dioxide it readily dissolves in it and reacts with water to form one of its Oxo acids known as sulphurous acid.
 $ S{O_{2\left( g \right)}} + {H_2}{O_{\left( {aq} \right)}} \to {H_2}S{O_{3\left( {aq} \right)}} $
Sulphurous acid is one of the unstable Oxo acids of sulphur hence, it undergoes decomposition reaction again to yield sulphur dioxide and water again.
Due to high instability of sulphurous acid it is not possible to obtain it in pure state. In order to overcome this problem sulphur acid is produced in its salt form.
On treating sulphur with water add potassium sulfite, after completion of reaction we get potassium bisulfite which is stable in nature.
 $ S{O_2} + {H_2}O + {K_2}S{O_3} \to 2KHS{O_3} $ .

Note :
Sulphur dioxide reacts with oxygen in the presence of catalyst vanadium pentoxide to form sulphur trioxide.
 $ 2S{O_2} + {H_2}O\dfrac{{{V_2}{O_5}}}{{catalyst}}2S{O_3} $
Sulphur dioxide is used widely in refining of sugars and in petroleum plants, as a disinfectant for surface sterilization, as a solvent etc.