Drugs & Medication

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 or colourless solid or liquid
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 1 0
Flash point	Non-flammable
R/S statement	R: none S: none
RTECS number	VZ4725000
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)

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.

Contents 1 Crystal structure 2 Biological importance 3 Salt throughout history 4 In religion 5 Production and use 5.1 Synthetic Uses 5.2 Flavour enhancer 5.3 Biological uses 5.4 De-icing 5.5 Additives 6 Other facts 7 See also 8 External links

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 left as green spheres, are arranged in a cubic close-packing, while the smaller sodium ions, shown to the left as blue spheres, fill the octahedral gaps between them.

Each ion is surrounded by six 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.

Biological importance

Sodium chloride is essential to life on Earth. Most biological tissues and body fluids contain a varying amount of salt.

Salt throughout history

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.

During his protests in India, Gandhi performed the famous salt march to challenge the British-imposed monopoly on salt.

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, a reference to salt's great value in the ancient world. Most of the time when talking about salt, the Bible is speaking of wisdom or age and wisdom combined.

In the native Japanese religion shinto, salt is seen as "corrupt" and can be used to purify (bless) locations and people, such as in Sumo Wrestling.

Production and use

Nowadays, salt is 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

2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH

Sodium metal is produced commercially through the electrolysis of liquid sodium chloride. This is done in a Down's cell in which the NaCl 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

Flavour enhancer

Main article: Edible salt

Salt is commonly used as a flavour 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, particularly in colder climates where the required intake is much lower. 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.

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. It has also been used to disinfect wounds. In medieval times salt would be rubbed into household surfaces as a cleansing agent.

De-icing

While salt was 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, see Grit bin. This works because salt and water form a eutectic mixture that has about a 10°C lower freezing point than pure water (see Freezing-point depression): the ions prevent regular ice crystals from forming (below −10°C salt will not prevent water from freezing). Concerns are arising that this use may be harmful to the environment though, and, in Canada, norms were developed to minimize the use of salt in de-icing.

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.

Other facts

• Salty soil is generally unfit for agriculture, hence the practice of salting the earth.

• Due to its high concentration of salt, the Dead Sea has such a high density that some objects which are not normally buoyant can float on its surface. Humans float easily, having a density slightly less than that of pure water. (Only 8% of the salt in the Dead Sea is sodium chloride; 53% is magnesium chloride, 37% is potassium chloride.)

• The cities of Cincinnati, Detroit and Hutchinson, Kansas are on top of active salt mines.

• The Third Reich stored vast amounts of money, paintings and artworks in salt mines, and many important documents and items continue to be stored in former salt mines to this day. Salt mines are also used to store nuclear waste.

See also

• Edible salt

External links

• Salt Institute website
• Salt Archive website
• Video of rotating rock salt unit cell (divx, 378kb)
• Salt United States Geological Survey Statistics and Information