What is oleum?

Oleum is a solution of sulphur trioxide (SO₃) dissolved in concentrated sulphuric acid (H₂SO₄). It is also known as fuming sulphuric acid because it releases fumes of sulphur trioxide when exposed to air.

The general chemical formula of oleum is represented as H₂S₂O₇ (disulphuric acid), although commercial oleum may contain different amounts of dissolved sulphur trioxide. It is produced during the Contact Process, which is widely used for the industrial manufacture of sulphuric acid.

Oleum is highly reactive and is used in chemical industries for producing sulphuric acid, detergents, dyes, explosives, and other chemical compounds. Due to its corrosive nature, it must be handled carefully with proper safety measures. Studying oleum helps students understand industrial chemistry, chemical reactions, and the large-scale production of important compounds.