Nitric Acid

Nitric Acid, colorless, corrosive liquid that has the chemical formula HNO₃. Medieval alchemists called it aqua fortis (strong water). Commercially, nitric acid is made by the action of sulfuric acid on sodium nitrate. Nitric acid is also made by the catalytic oxidation of ammonia. Nitric acid is a strong acid and a strong oxidizing agent. When dropped on the skin, the acid produces a yellow coloration because of the reaction of the acid with certain proteins to form yellow xanthoproteic acid.

The concentrated nitric acid used commercially contains about 71 percent HNO ₃; the rest is water. Fuming nitric acid, which also is widely used commercially, consists of nitric acid with gaseous nitrogen oxide in solution. It is red or brown in color and more active than other forms of nitric acid. Ordinary and fuming nitric acid have many applications. They are used in chemical synthesis, in the nitration of organic materials to form nitro compounds (compounds that contain an NO₂ group), and in the manufacture of dyes and explosives. Nitric acid melts at -42° C (-44° F) and boils at 83° C (181° F).

The salts of nitric acid are called nitrates. Potassium nitrate, or saltpeter, and sodium nitrate are the nitrates of greatest commercial importance. Nearly all nitrates are soluble in water; one of the exceptions is bismuth subnitrate, BiONO₃· H₂O, which is used in medicine for treating intestinal disorders. Amitol, a powerful explosive, is a mixture of ammonium nitrate and trinitrotoluene (TNT). The reaction of nitric acid with organic compounds yields many important nitrates, such as nitroglycerin and nitrocellulose. Calcium, sodium, potassium, and ammonium nitrates are used in fertilizers to provide a source of nitrogen for plant growth.