Nitric acid has the chemical formula HNO3. At standard temperature and pressure it is a colorless, corrosive liquid and it decomposes at a temperature of 181°F (83°C). If nitric acid is not pure it is generally colored due to the presence of nitrogen dioxide dissolved in the liquid. The decomposition of nitric acid into nitrogen, water, and oxygen is a naturally occurring reaction which is catalyzed by light.
Nitric acid is produced industrially by the oxidation of ammonia over a platinum catalyst at a high temperature. The resultant gas is then dissolved in water to give nitric acid. Nitric acid is completely ionized in solution and as such it is a strong acid and an efficient oxidizing reagent. Nitric acid is sufficiently strong as an oxidizing agent to be able to oxidize sulfur and phosphorus directly to sulfuric acid and phosphoric acid.Carbon is oxidized to directly produce carbon dioxide and nitrogen dioxide. A number of metals are not affected by hydrochloric acid and other acids but nitric acid will dissolve them and release oxides of nitrogen in the process.Copper will react with nitric acid to produce a blue solution of copper (II) nitrate along with water and nitrogen dioxide. The only common metals not dissolved by nitric acid are gold and platinum.
When nitric acid reacts with a metal the products that result are dependant upon the concentration of the acid used. This process is complicated by the fact that nitric acid acts as a strong oxidizing agent as well as an acid. Reactive metals will react with nitric acid to give the metal nitrate and hydrogen gas. Less reactive metals do not produce hydrogen at all. With dilute acid one of the principal products is nitrogen monoxide, while with concentrated acid it is nitrogen dioxide. In practical terms both reactions give the brown fumes normally associated with nitrogen dioxide, because the nitrogen monoxide rapidly reacts with the oxygen in the air to produce nitrogen dioxide. Treating metals (iron, chromium, aluminum, and calcium) with concentrated nitric acid can produce a protective oxide layer over the metal that halts further reactions.
Nitric acid reacted with a base will give the nitrate of the salt and water. The reaction with carbonates gives the nitrate salt, water, and carbon dioxide.
Nitric acid can be thermally decomposed to give water, nitrogen dioxide, and oxygen. If the products are collected over water only oxygen is collected as the nitrogen dioxide dissolves in the water.
Nitric acid is used in the production of fertilizers (after the nitric acid is turned into ammonium nitrate), dyes, explosives [including trinitrotoluene (TNT)], various polymers (such as nylon and terylene), and some drugs. The old (alchemical) name of nitric acid is aqua fortis meaning "strong water." In the 1990s production of nitric acid in the United States was in excess of 6 megatons.
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