HNO3

Nitric acid, with chemical formula HNO3, is a mineral acid that is highly corrosive and a strong oxidizer. It is typically colorless but can appear yellow to brown due to nitrogen dioxide impurities; concentrated solutions often release fumes. The acid is miscible with water and is widely used in chemical manufacture and processing.

Production and supply are dominated by the Ostwald process. In this route, ammonia is oxidized to nitrogen monoxide over a catalyst, then further oxidized to nitrogen dioxide and absorbed in water to form nitric acid. Concentrated solutions are often produced and sold as around 68–70% HNO3, with higher concentrations obtainable under specialized conditions. The acid is also produced as a byproduct in some industrial processes.

Reactivity and applications. HNO3 is both a strong acid and a powerful oxidizer, capable of nitrating organic substrates in the presence of a catalyst or concentrated acid. It is essential in the production of fertilizers (nitrates such as ammonium nitrate), explosives (nitro compounds), and various organic and inorganic chemicals. It is used for metal cleaning and surface treatments, glass etching, and as a dehydrating and oxidizing agent in selected reactions. Reactions with metals typically liberate nitrogen oxides and metal nitrates; the outcome depends on concentration and conditions (dilute nitric acid tends to release NO, concentrated acid releases NO2).

Safety and handling. Nitric acid is highly corrosive to skin, eyes, and tissues and releases toxic fumes. It reacts vigorously with reducing agents and organic materials, posing fire and explosion risks in some cases. It is stored in compatible containers, usually glass or certain plastics, and handled in well-ventilated areas with appropriate protective equipment. Environmental releases can contribute to waterway eutrophication and soil acidification.