Nitric acid
Introduction
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%.
History
The alchemist Albert the Great, in the 13th century, is credited with the discovery of nitric acid. The alchemical name for nitric acid was aqua fortis (strong water), reflecting the acid's ability to dissolve metals such as copper, silver, and gold. The name 'nitric acid' was first used in the early 19th century and stems from the Latin 'nitrum', referring to naturally occurring deposits of potassium nitrate, also known as saltpeter.
Production
Nitric acid is made by the Ostwald method. The process includes the catalytic oxidation of ammonia to nitric oxide, which is then oxidized to nitrogen dioxide, and finally absorbed in water to form nitric acid.
Properties
Nitric acid is a strong acid and a powerful oxidizing agent. The acid is colorless in its pure form and turns yellow due to decomposition into oxides of nitrogen and water. Most commercially available nitric acid has a concentration of 68%. When the acid is above 86% concentration, it is referred to as fuming nitric acid, which can be further classified into white fuming nitric acid and red fuming nitric acid.
Uses
Nitric acid has a wide variety of uses, including the production of fertilizers, dyes, as well as being a strong oxidizing agent. It is also used in rocket propellants, and in the production of explosives such as nitroglycerin and TNT. In metallurgy and refining, the acid is used to clean metals and etch circuit boards.
Safety
Nitric acid poses a significant health hazard due to its corrosiveness and toxicity. Direct contact with the skin can cause severe burns and the vapor can cause damage to the eyes and respiratory tract. Proper safety measures should be taken when handling nitric acid, including the use of personal protective equipment.
Environmental Impact
Nitric acid plays a role in the nitrogen cycle and is a significant contributor to acid rain. The production of nitric acid also results in the release of nitrogen oxides, which are potent greenhouse gases.