Potassium Fluoride

OVERVIEW

Potassium fluoride (poe-TAS-ee-yum FLU-ride) is a colorless or white crystalline or powdery compound with no odor, but a sharp, salty taste. It has somewhat limited uses in industry and chemical research.

HOW IT IS MADE

In one method for making potassium fluoride, potassium carbonate (K₂CO₃) is dissolved in hydrofluoric acid, resulting in the formation of potassium bifluoride (KHF₂): K₂CO₃ + 2H₂F₂ → 2KHF₂ + CO₂ + H₂O. The potassium bifluoride is then heated to form potassium fluoride and hydrogen fluoride: KHF₂ → KF + HF.

KEY FACTS

OTHER NAMES:

Potassium monofluoride

FORMULA:

KF

ELEMENTS:

Potassium, fluorine

COMPOUND TYPE:

Binary salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

58.10 g/mol

MELTING POINT:

858°C(1580°F)

BOILING POINT:

1502°C(2736°F)

SOLUBILITY:

Soluble in cold water; very soluble in hot water; insoluble in ethyl alcohol; soluble in hydrofluoric acid (H₂F₂)

Potassium fluoride can also be prepared by the direct reaction between hydrofluoric acid and potassium hydroxide: H₂F₂ + 2KOH → 2KF + 2H₂O. The potassium fluoride thus formed is then dried and crystallized or converted to powder form.

Interesting Facts

• In France, potassium fluoride is sometimes added to table salt to help prevent dental cavities.
• Potassium fluoride can not be shipped out of the United States to other countries without a special license from the U.S. Department of Commerce because the compound is an important raw material in the manufacture of certain chemical weapons.

COMMON USES AND POTENTIAL HAZARDS

Potassium fluoride is used as a fluoridating agent—a substance that provides fluorine atoms to other compounds—in the preparation of organic chemicals. It also finds some use in the field of metallurgy, where it is used as a flux, to finish metals, to make coatings for metals, and in tin plating. Potassium fluoride is used to frost and etch glass, as in the manufacture of some optical glasses, and to make insecticides, pesticides, and disinfectants.

Potassium fluoride is irritating to the skin, eyes, and respiratory system. It is moderately toxic by ingestion, causing nausea, vomiting, diarrhea, and stomach pains. In larger doses, it can cause damage to the brain, kidneys, and heart. Long-term exposure to potassium fluoride can cause damage to the teeth and bones. One condition that can develop is called fluorosis. Symptoms of the condition include brittle bones, weight loss, anemia, hardening of the ligaments, and stiffness of the joints.

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.

METALLURGY

The study of the properties and structures of metals.

FOR FURTHER INFORMATION

Hernandez, Lucúla Pazos. "Prevention of Dental Caries Through Salt Fluoridation in Mexico." http://www.ibiblio.org/taft/cedros/english/newsletter/n3/prevent.html (accessed on October 31, 2005).

"Potassium Fluoride." Patnaik, Pradyot. Handbook of Inorganic Chemicals. New York: McGraw-Hill, 2003, 754-755.

"Potassium Fluoride, Anhydrous." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/p5774.htm (accessed on October 31, 2005).

"Silver Production on the Moon." The Artemis Project. http://asi.org/adb/02/13/02/silicon-production.html (accessed on October 31, 2005).