亚硝酸是一种无机弱酸，是区分伯、仲、叔脂肪胺或芳香胺的鉴定试剂。

• 分子式：HNO₂
• 分子量：47.013
• 键长：N—OH为143pm，N—O为118pm。
• 键角：HON为102°，ONO为111°。

Nitrous acid (molecular formula HNO₂) is a weak and monobasic acid known only in solution and in the form of nitrite salts.

Nitrous acid is used to make diazides from amines; this occurs by nucleophilic attack of the amine onto the nitrite, reprotonation by the surrounding solvent, and double-elimination of water. The diazide can then be liberated to give a carbene or carbenoid.