Sodium Fluoride

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Sodium Fluoride

OVERVIEW

Sodium fluoride (SO-dee-um FLOR-ide) is a colorless to white crystalline solid or powder. It is best known for its role in efforts to prevent tooth decay. It may be added to toothpastes or mouthwashes or to municipal water supplies for this purpose. Although the practice of fluoridating water is now widespread in the United States, it remains the subject of controversy regarding its potential health effects on humans.

KEY FACTS

OTHER NAMES:

Sodium monofluoride

FORMULA:

NaF

ELEMENTS:

Sodium, fluorine

COMPOUND TYPE:

Binary salt (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

41.99 g/mol

MELTING POINT:

996°C (1824°F)

BOILING POINT:

1704°C (3099°F)

SOLUBILITY:

Moderately soluble in water; insoluble in ethyl alcohol

HOW IT IS MADE

Sodium fluoride occurs naturally as the mineral villiaumite, although the compound is not produced commercially from that source. Some sodium fluoride is obtained as a byproduct of the manufacture of phosphate fertilizers. In that process, apatite (a form of calcium phosphate that also contains fluorides and/or chlorides) is crushed and treated with sulfuric acid (H₂SO₄). The products of that reaction include phosphoric acid (H₃PO₄), calcium sulfate (CaSO₄), hydrogen fluoride (HF), and silicon tetrafluoride (SiF₄). The hydrogen fluoride and silicon tetrafluoride can then be converted into sodium fluoride. The compound can also be produced by treating hydrogen fluoride with sodium carbonate (Na₂CO₃):

2HF + Na₂CO₃ → 2NaF + H₂O + CO₂

COMMON USES AND POTENTIAL HAZARDS

More than 50 years of research has shown that sodium fluoride and other fluorides are effective in preventing tooth decay. Based on this information, sodium fluoride or some other compound of fluorine is now added to most toothpastes made in the United States. Dentists regularly treat their patients' teeth with fluoride washes to make them more resistant to decay. Most cities and towns in the United States add sodium fluoride or a comparable compound to the municipal water supply to reduce the rate of dental caries (cavities). Some people who live where fluoride is not added to their water supply take sodium fluoride pills to improve their dental health. The American Dental Association and the World Health Organization recommend fluoridation of drinking water at a level between 0.7 and 1.2 parts per million.

In spite of these trends, opposition to the use of fluorides against tooth decay remains strong in the United States and other parts of the world. Opponents are not convinced that there is sufficient evidence for the claims that fluoridation decreases the rate of tooth decay. They suggest that fluorides may cause cancer and a host of other health problems. And they argue that fluoridating public water supplies removes the choice that individuals should have as to whether or not they want to use fluorides in their dental health program.

Interesting Facts

Some of the opposition to the fluoridation of water is based on a misunderstanding of the difference between fluorine, the element, and fluorides, compounds of fluorine, such as sodium fluoride and potassium fluoride. Fluorides have very different physical, chemical, and biological properties from the element fluorine. For example, fluorine gas is a highly toxic gas that reacts violently with most substances, including water. Flourides, on the other hand, are relatively inert (unreactive) and safe to ingest in small amounts.

Sodium fluoride has a number of commercial and industrial uses in addition to those related to dental health. Those uses include:

As a wood preservative;
In the production of certain types of pesticides and as an insecticide for ant and roach control;
In the preparation of other fluoride salts;
In electroplating operations;

In the degassing (removal of gas pockets) during the manufacture of steel;
For the manufacture of glass and vitreous (glass-like) enamels;
In detection systems for radiation in the ultraviolet and infrared regions of the electromagnetic spectrum; and
For disinfecting equipment used in breweries and wineries.

The discussion about fluoridation of public water supplies is sometimes made more difficult because of the fact that sodium fluoride poses some real health hazards to humans. It is a skin, eye, and respiratory irritant that can cause burning if spilled on the skin or in the eyes. If swallowed, it can cause burning of the digestive tract, nausea, vomiting, abdominal pain, stupor, general weakness, tremors, convulsions, collapse, respiratory and cardiac failure, and death. Ingestion of as little as five grams of sodium fluoride can result in death. A condition known as fluorosis is also associated with high doses of sodium fluoride. Fluorosis is characterized by a yellowing and increased brittleness of teeth and bones. Although these conditions are all very serious, they appear only at doses many thousands of times greater than one receives from fluorides in toothpastes and public water supplies.

Words to Know

ELECTROPLATING: A process by which a thin layer of one metal is deposited on top of a second metal by passing an electric current through a solution of the first metal.