sodium chloride

Properties

Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals. Sodium chloride is odorless but has a characteristic taste. It is an ionic compound, being made up of equal numbers of positively charged sodium and negatively charged chloride ions. When it is melted or dissolved in water the ions can move about freely, so that dissolved or molten sodium chloride is a conductor of electricity; it can be decomposed into sodium and chlorine by passing an electrical current through it (see electrolysis).

Natural Occurrence and Commercial Preparation

Nearly all chemical compounds that contain either sodium or chlorine are ultimately derived from salt. Salt is widely and abundantly distributed in nature. It makes up nearly 80% of the dissolved material in seawater, and is the greater part of dissolved matter in the Dead Sea, the Great Salt Lake, and in salt wells in various parts of the world. It is also widely distributed in solid form. The mineral halite is pure salt. Rock, or mineral, salt is usually less pure; it is found in large deposits in the United States, notably in New York, Michigan, Ohio, Kansas, Texas, and Louisiana, and also in Great Britain, France, Germany, Russia, China, and India.

The manufacture and use of salt is one of the oldest chemical industries. Salt is mined from deposits or is obtained as a brine by introducing water into the deposits to dissolve the salt and then pumping the solution to the surface. Salt is also obtained by evaporation of seawater, usually in shallow basins warmed by sunlight; salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Most salt for table use is obtained from seawater. It is usually not pure sodium chloride—it may contain natural impurities that provide dietary minerals, or small amounts of other substances (e.g., magnesium carbonate, hydrated calcium silicate, or tricalcium phosphate) may be added to prevent lumping.

Biological Importance and Uses

Salt is important in many ways. It is an essential part of the diet of both humans and animals and is a part of most animal fluids, such as blood, sweat, and tears. It aids digestion by providing chlorine for hydrochloric acid, a small but essential part of human digestive fluid. Persons with hypertensive heart disease often must restrict the amount of salt in their diet.

Salt is widely used as a seasoning for foods and is used in curing meats and preserving fish and other foods. Iodized table salt usually contains small amounts of potassium iodide, sodium carbonate, and sodium thiosulfate. As a chemical salt is used in making glass, pottery, textile dyes, and soap. It is used in large amounts to melt ice and snow on streets and highways. The major use of salt is as a raw material for the production of chlorine, sodium metal, and sodium hydroxide; it is also used in large amounts in the Solvay process for making sodium carbonate. Historically, salt has been used as money; a high tax on salt was a contributing cause of the French Revolution.

Bibliography

See G. L. Eskew, Salt, the Fifth Element (1948); D. W. Kaufmann, ed., Sodium Chloride (1968); G. Mamantov and R. Marassi, ed., Molten Salt Chemistry (1987).

For sodium in the diet, see salt.

Sodium chloride
IUPAC name	Sodium chloride
Other names	Common salt; halite; table salt
Identifiers
CAS number	7647-14-5
RTECS number	VZ4725000
Properties
Molecular formula	NaCl
Molar mass	58.442 g/mol
Appearance	white and crystalized
Density	2.16 g/cm³, solid
Melting point	801 °C
Boiling point	1465 °C (1738 K)
Solubility in water	35.9 g/100 mL (25 °C)
Structure
Coordination geometry	Octahedral
Hazards
MSDS	External MSDS
Main hazards	Irritant and Might Sting
NFPA 704	0 1 0
R-phrases	36
S-phrases	none
Flash point	Non-flammable
Related Compounds
Other anions	NaF, NaBr, NaI
Other cations	LiCl, KCl, RbCl, CsCl, MgCl2, CaCl2
Related salts	Sodium acetate
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms. As the main ingredient in edible salt, it is commonly used as a condiment and food preservative. In one gram of sodium chloride, there are approximately 0.3933 grams of sodium, and 0.6067 g of chlorine.

Production and use

Salt is currently produced by evaporation of seawater or brine from other sources, such as brine wells and salt lakes, and by mining rock salt, called halite. In 2002, world production was estimated at 210 million metric tonnes, the top five producers being the United States (40.3 million tonnes), China (32.9), Germany (17.7), India (14.5), and Canada (12.3).^[1]

While most people are familiar with the many uses of salt in cooking, they might be unaware that salt is used in a plethora of applications, from manufacturing pulp and paper to setting dyes in textiles and fabric, to producing soaps and detergents. In most of Canada and the northern USA, large quantities of rock salt are used to help clear highways of ice during winter, although "Road Salt" loses its melting ability at temperatures below -15°C to -20°C (5°F to -4°F). .

Jordanian and Israeli salt evaporation ponds at the south end of the Dead Sea

Mounds of salt, Salar de Uyuni, Bolivia.

Modern rock salt mine near Mount Morris, New York.

Evaporation lagoons, Aigues-Mortes, France

Synthetic uses

Salt is also the raw material used to produce chlorine which itself is required for the production of many modern materials including PVC and pesticides. Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the chemical equation

2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH

Sodium metal is produced commercially through the electrolysis of liquid sodium chloride. This is done in a Down's cell in which sodium chloride is mixed with calcium chloride to lower the melting point below 700 °C. As calcium is more electropositive than sodium, no calcium will be formed at the cathode. This method is less expensive than the previous method of electrolyzing sodium hydroxide.

Sodium chloride is used in other chemical processes for the large-scale production of compounds containing sodium or chlorine. In the Solvay process, sodium chloride is used for producing sodium carbonate and calcium chloride. In the Mannheim process and in the Hargreaves process, it is used for the production of sodium sulfate and hydrochloric acid.

Food Uses

Main article: Salt

Salt is commonly used as a flavour enhancer and preservative for food and has been identified as one of the basic tastes. Unfortunately, given its history, this has resulted in large sections of the developed world ingesting salt massively in excess of the required intake. ^{[citation needed]}. This causes elevated levels of blood pressure (hypertension) in some, which in turn is associated with increased risks of heart attack and stroke. Consuming salt in excess can also dehydrate the human body. Salt also has a practical use in cooking in that it raises the boiling point of water, thus allowing a food to cook slower and more thoroughly on a slow boil.

Biological uses

Many microorganisms cannot live in an overly salty environment: water is drawn out of their cells by osmosis. For this reason salt is used to preserve some foods, such as smoked bacon or fish and can also be used to detach leeches that have attached themselves to feed. It has also been used to disinfect wounds. In medieval times salt would be rubbed into household surfaces as a cleansing agent.

Crystal structure

Sodium chloride forms crystals with cubic symmetry. In these, the larger chloride ions, shown to the right as green spheres, are arranged in a cubic close-packing, while the smaller sodium ions, shown to the right as blue spheres, fill the octahedral gaps between them.

The crystal structure of sodium chloride. Each atom has six nearest neighbors, with octahedral geometry.

Each ion is surrounded by six ions of the other kind. This same basic structure is found in many other minerals, and is known as the halite structure. This arrangement is known as cubic close packed (ccp).

It is held together with an ionic bond and electrostatic forces.

Salt is also known in the chemical world as a nuclear additive.

Road salt

De-icing

While salt was once a scarce commodity in history, industrialized production has now made salt plentiful. About 51% of world output is now used by cold countries to de-ice roads in winter, both in grit bins and spread by winter service vehicles. This works because salt and water form an eutectic mixture. For a solution of table salt (sodium chloride, NaCl) in water, the freezing temperature becomes -21 °C (-6 °F) under controlled lab conditions. In practice, however, sodium chloride can melt ice only down to about -9 °C (15 °F).

Additives

Table salt sold for consumption today is not pure sodium chloride. In 1911 magnesium carbonate was first added to salt to make it flow more freely.^[1] In 1924 trace amounts of iodine in form of sodium iodide, potassium iodide or potassium iodate were first added, creating iodized salt to reduce the incidence of simple goiter.^[2]

Salt for de-icing in the UK typically contains sodium hexacyanoferrate (II) at less than 100ppm as an anti-caking agent. In recent years this additive has also been used in table salt.

Common chemicals

Chemicals used in de-icing salts are mostly found to be sodium chloride (NaCl) or calcium chloride (CaCl₂). Both are similar and are effective in de-icing roads. When these chemicals are produced, they are mined/made, crushed to fine granules, then treated with an anti-caking agent. Adding salt lowers the freezing point of the water, which allows the liquid to be stable at lower temperatures and allows the ice to melt.

Alternative de-icing chemicals have also been used. Chemicals such as calcium magnesium acetate and potassium formate are being produced. These chemicals have few of the negative chemical effects on the environment commonly associated with NaCl and CaCl₂.^[3][4]

See also

Wikibooks Cookbook has an article on

Salt

Wikimedia Commons has media related to:

Sodium chloride

• Biosalinity
• Black salt
• Edible salt
• Halite, the mineral form of sodium chloride
• Salinity
• Soap
• Salting the earth

References

External links

• The Salt Manufacturers Association website
• Salt Institute website
• Salt Archive website
• Video of rotating rock salt unit cell (divx, 378kb)
• Salt United States Geological Survey Statistics and Information
• US Road Management website
• Salt Intake in Cold Weathernrm:Sé (NaCl)

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