Sodium chloride

For sodium in the diet, see Edible salt.

Sodium chloride
General
Systematic name	Sodium chloride
Other names	Common salt, halite, table salt
Molecular formula	NaCl
Molar mass	58.442 g/mol
Appearance	white and crystalized
CAS number	[7647-14-5]
Properties
Density and phase	2.16 g/cm³, solid
Solubility in water	35.9 g/100 ml (25 °C)
Melting point	801 °C (1074 K)
Boiling point	1465 °C (1738 K)
Structure
Coordination geometry	Octahedral
Crystal structure	Face centered cubic
Hazards
MSDS	External MSDS
Main hazards	Irritant and Might Sting
NFPA 704	0 0 0
Flash point	Non-flammable
R/S statement	R: none S: none
RTECS number	VZ4725000
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	NaF, NaBr, NaI
Other cations	LiCl, KCl, RbCl, CsCl, MgCl2, CaCl2
Related salts	Sodium acetate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Modern rock salt mine near Mount Morris, New York

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

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.

Mounds of salt, Salar de Uyuni, Bolivia.

History

See main article: History of salt

Salt's preservative ability was a foundation of civilization. It eliminated dependency on the seasonal availability of food and allowed travel over long distances. By the Middle Ages, caravans consisting of as many as forty thousand camels traversed four hundred miles of the Sahara bearing salt, sometimes trading it for slaves.^{[citation needed]}

During his protests in India, Gandhi led the famous salt march to challenge the British-imposed monopoly on salt.^{[citation needed]}

Sources

Historically, there have been two main sources for common salt: sea water and rock salt. Rock salt occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes, playas, and seas. Salt beds may be up to 350 meters (m) thick and underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and under much of the Michigan basin. Other deposits are in Ohio, Kansas, New Mexico, Nova Scotia, and Saskatchewan. In the United Kingdom underground beds are found in Cheshire and around Droitwich.

Salt is extracted from underground beds either by mining or by solution mining using water or brine. In solution mining the salt reaches the surface as brine, which is then turned into salt crystals by evaporation.

Crystal structure

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

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.

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.

In religion

There are thirty-five references (verses) to salt in the Bible (King James Version), the most familiar probably being the story of Lot's wife, who was turned into a pillar of salt when she disobeyed the angels and looked back at the wicked city of Sodom (Genesis 19:26). In the Sermon on the Mount, Jesus also referred to his followers as the "salt of the earth." The apostle Paul also encouraged Christians to "let your conversation be always full of grace, seasoned with salt" (Colossians 4:6) so that when others enquire about their beliefs, the Christian's answer generates a 'thirst' to know more about Christ.

In the native Japanese religion Shinto, salt is used for ritual purification of locations and people, such as in Sumo Wrestling.

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.

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).

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.

Solubility of NaCl in various solvents (g NaCl / 100 g of solvent at 25 °C)
H2O	36
Liquid ammonia	3.02
Methanol	1.4
Formic acid	5.2
Sulfolane	0.005
Acetonitrile	0.0003
Acetone	0.000042
Formamide	9.4
Dimethylformamide	0.04
Reference: Burgess, J. Metal Ions in Solution (Ellis Horwood, New York, 1978) ISBN 0-85312-027-7

Flavor enhancer

Salt is commonly used as a flavor enhancer 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 ^{[citation needed]}, which in turn is associated with increased risks of heart attack and stroke. Consuming salt in excess can also dehydrate the human body.

File:Ionicbond.JPG

Impression of two ions, for example Na⁺ and Cl^- forming an ionic bond. The electron orbitals generally do not overlap (i.e., molecular orbitals are not formed), because each of the ions reached the lowest energy state and the bond is based only (ideally) on the electrostatic interactions between positive and negative ions.

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 (although it causes a great deal of pain). In medieval times salt would be rubbed into household surfaces as a cleansing agent.

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

The 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. 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. ^{[citation needed]}

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 are being produced. These chemicals have few of the negative chemical effects on the environment commonly associated with NaCl and CaCl₂. ^{[citation needed]}

See also

• Black salt
• Edible salt
• Halite
• Salinity
• Soap

References

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External links

• The Salt Manufacturers Association
• Salt Institute
• Salt Archive
• 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 Weather

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