Nitric Acid
Overview
Nitric acid (NYE-trik AS-id) is a colorless to yellowish liquid with a distinctive acrid (biting), suffocating, or choking odor. The acid tends to decompose when exposed to light, producing nitrogen dioxide (NO2), itself a brownish gas. The yellowish tinge often observed in nitric acid is caused by the presence of small amounts of the nitrogen dioxide. Nitric acid is one of the strongest oxidizing agents known and attacks almost all metals with the notable exceptions of gold and platinum.
Key Facts
Other Names:
Aqua fortis; engraver's acid; azotic acid
Formula:
HNO3
Elements:
Hydrogen, nitrogen, oxygen
Compound Type:
Inorganic acid
State:
Liquid
Molecular Weight:
63.01 g/mol
Melting Point:
−41.6°C (−42.9°F)
Boiling Point:
83°C (180°F); decomposes
Solubility:
Miscible with water; decomposes in ethyl alcohol; reacts violently with most organic solvents
Nitric acid has been known to scholars for many centuries. Probably the earliest description of its synthesis occurs in the writings of the Arabic alchemist Abu Musa Jabir ibn Hayyan (c. 721–c. 815), better known by his Latinized name of Geber. The compound was widely used by the alchemists, although they knew nothing of its chemical composition. It was not until the middle of the seventeenth century that an improved method for making nitric acid was invented by German chemist Johann Rudolf Glauber (1604–1670). Glauber produced the acid by adding concentrated sulfuric acid (H2SO4) to saltpeter (potassium nitrate; KNO3). A similar method is still used for the laboratory preparation of nitric acid, although it has little or no commercial or industrial value.
The chemical nature and composition of nitric acid were first determined in 1784 by the English chemist and physicist Henry Cavendish (1731–1810). Cavendish applied an electric spark to moist air and found that a new compound-nitric acid-was formed. Cavendish was later able to determine the acid's chemical and physical properties and its chemical composition. The method of preparation most commonly used for nitric acid today was one invented in 1901 by the Russian-born German chemist Friedrich Wilhelm Ostwald (1853–1932). The Ostwald process involves the oxidation of ammonia over a catalyst of platinum or a platinum-rhodium mixture.
Today, nitric acid is one of the most important chemical compounds used in industry. It ranks number thirteen among all chemicals produced in the United States each year. In 2005, about 6.7 million metric tons (7.4 million short tons) of the compound were produced in the United States.
How It Is Made
Although several methods for the preparation of nitric acid are theoretically available, only one finds much commercial use: the direct oxidation of ammonia, an updated and improved version of the traditional Ostwald process. In this method, ammonia is heated and reacted with air over a catalyst, most commonly a mixture of rhodium and platinum metals. That reaction results in the formation of nitric oxide (NO), which is then converted to nitrogen dioxide (NO2). The nitrogen dioxide reacts with water to form nitric acid.
Interesting Facts
- Alchemists called nitric acid aqua fortis, a term that means "strong water."
- Nitric acid is a component of acid rain, a form of pollution that results when substances such as nitrogen oxides react with water, oxygen, and other chemicals in the atmosphere.
Common Uses and Potential Hazards
The most common use for nitric acid is in the manufacture of ammonium nitrate, which, in turn, is used primarily as a fertilizer. About three-quarters of all nitric acid produced in the United States is used in fertilizers. The second most important application, accounting for about 10 percent of all nitric acid produced, is in the production of adipic acid [COOH(CH2)3COOH], used in the manufacture of nylon, polyurethanes, and other synthetic plastics. Nitric acid is also used to make a variety of metal nitrates and for the cleaning of metals. Small amounts of the compound are used for a variety of other applications, including:
- In the manufacture of explosives and fireworks;
- As a laboratory reagent in commercial, industrial, and academic research laboratories;
- In the processing of nuclear fuels;
- For the etching of metals; and
- In the manufacture of certain types of dyes.
Nitric acid is a highly toxic material. It attacks and destroys skin and other tissues, leaving a distinctive yellow scar caused by the destruction of proteins in the skin or tissue. If swallowed, inhaled, or spilled on the skin, it can cause a number of effects, including severe corrosive burns to the mouth, throat, and stomach; severe irritation or burning of the upper respiratory system, including nose, mouth, and throat; damage to the lungs; severe breathing problems; and burns to the eye surface, conjunctivitis, and blindness. In the most severe cases, the acid can cause death.
Words to Know
An ancient field of study from which the modern science of chemistry evolved. A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure. Able to be mixed; especially applies to the mixing of one liquid with another. A chemical reaction in which oxygen reacts with some other substance or, alternatively, in which some substance loses electrons to another substance, the oxidizing agent.For Further Information
"Concentrated Nitric Acid (70%)." International Chemical Safety Cards. http://www.cdc.gov/niosh/ipcsneng/neng0183.html (accessed on October 20, 2005).
"Material Safety Data Sheet." Hill Brothers Chemical Company. http://hillbrothers.com/msds/pdf/nitric-acid.pdf (accessed on October 20, 2005).
"Nitric Acid." Greener Industry. http://www.uyseg.org/greener_industry/pages/nitric_acid/1nitricAcidAP.htm (accessed on October 20, 2005).
"Nitric Acid." Scorecard. The Pollution Information Site. http://www.scorecard.org/chemical-profiles/summary.tcl?edf_substance_id=7697%2d37%2d2 (accessed on October 20, 2005).
See Also
Ammonia; Ammonium Nitrate; Nitrogen Dioxide; Nitroglycerin
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