Nitrous Acid Definition:

A compound with molecular formula HONO.

Nitrous Acid Explained:

This acid is used for the preparation of diazonium salts, the reaction with two a-hydrogen in ketones making oxime. It is usually made by reacting a solution containing sodium or potassium nitrite (sodium or potassium nitrate(III)) with hydrochloric acid. Nitrous acid is a weak acid and so you get the reaction: The acid and the nitrite form nitrous acid which then reacts with the amine.