Explain contact process for production of sulphuric acid.

Contact process:

i. In this process, first sulphur is burnt in air to form sulphur dioxide.

S + O₂→ SO₂

ii. Sulphur dioxide gas with excess air is passed over V₂O₅

catalyst so that sulphur trioxide is formed.

iii. When sulphur trioxide is dissolved in concentrated sulphuric acid, it forms fuming sulphuric acid or oleum.

SO₃ + H₂SO₄→ H₂S₂O₇

Oleum

iv. Oleum is diluted with water.

v. As a result, desired concentration of sulphuric acid can be obtained.

H₂S₂O₇ + H₂O → H₂SO₄