Chemical applications

Nitrous acid is the main chemophore in the Liebermann reagent, used to spot-test for alkaloids.

At high acidities , nitrous acid is protonated to give water and nitrosonium cations.

Reduction

With I^- and Fe²⁺ ions, NO is formed:

: 2 HNO₂ + 2 KI + 2 H₂SO₄ -> I₂ + 2 NO + 2 H₂O + 2 K₂SO₄