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Sodium chloride

(common salt, table salt, sea salt, rock salt)

CAS no: 7647-14-5   Formula: NaCl   Molecular weight: 58.443

Physical Data

Appearance: Colorless cubic crystalline solids

Melting point: 800.7C
Boiling point: 1465C

Density: 2.17 g/cm3
Solubility: 36.0 g/100 g H2Ograph

Thermodynamic Data

Enthalpy of formation: -411.2 kJ/mol
Gibbs energy of formation: -384.1 kJ/mol

Entropy: 72.1 J/mol K
Heat capacity: 50.5 J/mol K

Production and preparation

Occurs in nature as the mineral halite (rock salt), with a characteristic cubic shape. It is also found in great abundance in sea waters. It is produced by mining rock salt, by evaporations of brine from underground salt deposits and sea water. The world annual consumption of the salt exceeds 150 million tons and majority of sodium chloride is produced from Europe and North America. In the United States about 55% of the salt is produced from brine and about 30% is mined as rock salt.

Behavior and Chemical Properties

Sodium chloride is hygroscopic. It absorbs moisture from the atmosphere when the relative humidity is above 75%. The salt of commerce usually contains a small amounts of calcium and magnesium chlorides. These substances are deliquescent which absorb moisture in air and cause the salt to cake. However, sodium phosphate may be added so as to convert it to magnesium phosphate, which is not deliquescent and the salt then 'runs' better when pours out. Sodium chloride appears white when the crystals are very small and transparent when in large crystals. It is soluble in water with its solubility increases very slowly with increasing temperature. It is, however, almost insoluble in concentrated hydrochloric acid.

With concentrated sulfuric acid, hydrochloric acid (HCl) is formed, which readily dissolves in water (salt-cake method to produce HCl in industry):

HCl production

History and Uses

The use of rock salt has been known since 3000 BC. Around 200 BC, the common salt was used as a salary payment for services.

Sodium chloride is one of the essential nutrient factor, to be given orally as emectic, and isotonic solution to raise blood volume. With sugar, it is used orally to prevent dehydration. Sodium chloride is also widely used for preserving food.

It is one of the most important starting material for inorganic chemical manufacture. In fact, the first large-scale industrial chemical process, involving the use of sodium chloride for making sodium hydroxide, was devised by N. Leblanc (1742 - 1806). This process, however, is now largely superceded by the electrolytic process.

The Solvay process (or the ammonia soda process) was first carried out successfully in Belgium in the 1860s to produce sodium carbonate. It was patented in 1861 by the Belgian chemist Ernest Solvay (1838-1922). In this process, a concentrated brine is treated with ammonia and carbon dioxide (from calcium carbonate) to give sodium bicarbonate and ammonium chloride. The carbonate is produced by simply heating the bicarbonate compound. Ammonia is recovered when ammonium chloride is heated with lime.

Solvay process

Because of its great abundance and cheap production cost, sodium chloride is perhaps the only important source of chlorine (produced by electrolytic process) and hydrochloric acid for the production of chlorine-based chemical substances (running into more than 10 000 compounds). It is also used in the production of chlorinated organic compounds such as methanes, ethanes and vinyl chloride.

Large, pure sodium chloride crystals are also used to make infrared red or ultra violet optical windows, lenses and prisms.

It is also used in making a variety of house-hold materials such as soup, dyes and, using electrolytic process, to make sodium hypochlorite as bleaching agents. It is also used, in raw forms, for salting of roads to prevent the build up of icy patches.

Hazard, Storage and Handling

The salt must be kept in an air-tight bottle. Generally, the salt does not present any significant hazard to health. However, it may cause skin, eye or respiratory irritation. The oral lethal dose 50 percent kill for rats is about 3000 mg/kg.

Related links

Salt Institute - International trade association for sodium chloride. Provide information about the salt's usage, chemical production etc.

(Last update: February 2006)

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