Potassium Nitrate

OVERVIEW

Potassium nitrate (poe-TAS-ee-yum NYE-trate) is transparent, colorless, or white, and may be crystalline or powdery solid. It is odorless with a sharp, cool, salty taste. It is slightly hygroscopic, that is, having a tendency to absorb moisture from the air. Potassium nitrate, more commonly known as saltpeter or niter, has been used by humans for many centuries. Going back as far as ancient Chinese civilizations, the compound was used as an ingredient in fireworks, to preserve foods, to make incense burn more evenly, to increase the male sex drive, and for magic potions.

HOW IT IS MADE

Potassium nitrate is made commercially by reacting potassium chloride (KCl) with nitric acid (HNO₃) at high temperatures: 3KCl + 4HNO₃ ? 3KNO₃ + Cl₂ + NOCl + 2H₂O.

KEY FACTS

OTHER NAMES:

Niter; saltpeter; nitrate of potash

FORMULA:

KNO₃

ELEMENTS:

Potassium, nitrogen, oxygen

COMPOUND TYPE:

Salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

101.10 g/mol

MELTING POINT:

337°C (639°F)

BOILING POINT:

Not applicable; decomposes above 400°C (750°F)

SOLUBILITY:

Soluble in water and glycerol; slightly soluble in ethyl alcohol

The compound can also be obtained for use from natural sources. It occurs as a thin, whitish, glassy crust on rocks in sheltered areas, such as caves. In warm climates, potassium nitrate forms when bacteria decompose animal feces and other organic matter. The compound usually appears as a white powder on the surface of soil. These sources of potassium nitrate are of use on a small scale basis and have no commercial value.

COMMON USES AND POTENTIAL HAZARDS

The primary use of potassium nitrate is in explosives, blasting powders, gunpowder, fireworks, and matches. The compound is used as an oxidizing agent in such preparations. An oxidizing agent is a substance that provides oxygen for the combustion of some other material. For example, gunpowder, the oldest known explosive, is a mixture of potassium nitrate, charcoal (nearly pure carbon), and sulfur. When the mixture is ignited, the carbon and sulfur burn very rapidly to produce carbon dioxide (CO) and sulfur dioxide (SO₂. At the same time, the potassium nitrate decomposes to produce a variety of products, one of which is nitric oxide (NO). The rapid formation of very hot gases is responsible for the shock wave produced in the explosion.

Some other uses of potassium nitrate include:

• As a meat preservative that helps meats retain their bright red color;
• As a flux for soldering;
• In fertilizers, especially for use with crops such as tomatoes, potatoes, tobacco, leafy vegetables, citrus fruits, and peaches;
• In the manufacture of glasses and ceramics;
• As an additive for tobacco products that helps the tobacco burn more cleanly and smoothly;
• As an oxidizing agent in rocket propulsion systems;
• As a diuretic, a substance that increases the flow of urine from the body; and
• As a raw material in the manufacture of other potassium compounds.

Interesting Facts

• At one time, potassium nitrate was prepared by mixing manure with mortar or wood ash, soil, and an organic material, such as straw. The bed was kept moist with urine and turned often to speed decomposition of the organic matter. After a year, the bed was thoroughly watered, dissolving the potassium nitrate that had accumulated. It was then recrystallized and purified.
• In 1862, leaders of the Confederate Army ordered a chemistry professor at South Carolina College to teach farmers how to make potassium nitrate to ensure an adequate supply of the compound for use in making gunpowder.
• Gunpowder was probably first used as early as the eleventh century. The English natural philosopher Roger Bacon (1214–1294) described a method for making gunpowder in 1242.

Exposure to moderate amounts of potassium nitrate dust and fumes can result in irritation of the skin, eyes, and respiratory system. Symptoms may include sneezing, coughing, dizziness, drowsiness, and headache. Ingestion of the compound may result in nausea, vomiting, and severe abdominal pain. Exposure to large quantities of the compound may have more serious consequences because it interferes with the blood's ability to transport oxygen. In such cases, a person may experience shortness of breath, bluish skin, serious damage to the kidneys, unconsciousness, and even death. People who work directly with potassium nitrate are at greatest risk for such health problems.

Words to Know

FLUX

A material that lowers the melting point of another substance or mixture of substances or that is used in cleaning a metal.

FOR FURTHER INFORMATION

"Material Safety Data Sheet: Potassium Nitrate." Department of Chemistry, Iowa State University. http://avogadro.chem.iastate.edu/MSDS/KNO3.htm (accessed on November 3, 2005).

Multhauf, Robert P., and Christine M. Roane. "Nitrates." In Dictionary of American History. Edited by Stanley I. Kutler. 3rd ed., vol. 6. New York: Charles Scribner's Sons, 2003.

"Potassium Nitrate." Hazardous Substances Data Bank. http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+Potassium+Nitrate (accessed on November 3, 2005).

"Potassium Nitrate." International Chemical Safety Cards. http://www.inchem.org/documents/icsc/icsc/eics0184.htm (accessed on November 3, 2005).

"Potassium Nitrate." Skylighter. http://www.skylighter.com/potassium-nitrate.html (accessed on November 3, 2005).