Nitric acid

Nitric acid (HNO3), also known as aqua fortis and spirit of niter, is a highly corrosive and toxic strong acid.

Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming nitric acid. Depending on the amount of nitrogen dioxide present, fuming nitric acid is further characterized as white fuming nitric acid or red fuming nitric acid, at concentrations above 95%.

At room temperature, concentrated nitric acid will decompose slowly to nitrogen dioxide, water and oxygen, which can cause pressure buildup if the liquid is confined in a closed container.

Properties

Nitric acid is a strong acid and a powerful oxidizing agent. The major hazard posed by it is chemical burns as it carries out acid hydrolysis with proteins (amide) and fats (ester), which consequently decomposes living tissue (e.g. skin and flesh). Concentrated nitric acid stains human skin yellow due to its reaction with the keratin.

Production

Commercial grade nitric acid solutions are usually between 52% and 68% nitric acid. Production of nitric acid is via the Ostwald process, named after German chemist Wilhelm Ostwald. In this process, anhydrous ammonia is oxidized to nitric oxide, in the presence of platinum or rhodium gauze catalyst at a high temperature of about 500 K and a pressure of 9 atm.

Uses

The main use of nitric acid is for the production of fertilizers. Nitric acid is neutralized with ammonia to give ammonium nitrate. This application consumes 75-80% of the 26 million tonnes produced annually. The other main applications are for the production of explosives, nylon precursors, and specialty organic compounds.

Safety

Nitric acid is a corrosive acid and a powerful oxidizing agent. The major hazard posed by it is chemical burns as it carries out acid hydrolysis with proteins (amide) and fats (ester), which consequently decomposes living tissue (e.g. skin and flesh). Concentrated nitric acid stains human skin yellow due to its reaction with the keratin.

See also

• Sulfuric acid
• Hydrochloric acid
• Phosphoric acid
• Acetic acid

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