How is sulphuric acid manufacture by contact process ?

Explanation

Manufacture of sulphuric acid by contact process: The contact process involves the following steps.
(i) Initially sulphur dioxide is produced by burning sulphur or iron pyrites in oxygen/air.
`S+O_(2) rarr SO_(2)`
`4FeS_(2)+11O_(2)rarr 2Fe_(2)O_(3)+8SO_(2)`
(ii) Sulphur dioxide formed is oxidised to sulphur trioxide by air in the presence of a catalyst such as `V_(2)O_(5)` or platinised asbestos.
(iii) The sulphur trioxide is absorbed in concentrated sulphuric acid and converted into sulphuric acid by diluting it with water.
`SO_(3)+H_(2)SO_(4) rarr H_(2)S_(2)O_(7) overset(H_(2)O)rarr 2H_(2)SO_(4)`
(iv) To maximise the yield the plant is operated at 2 bar pressure and 720K. the sulphuric acid obtained in this process is over 96% pure.