Sodium chloride

For sodium in the diet, see Edible salt.

{| class="toccolours" border="1" style="float: right; clear: right; margin: 0 0 1em 1em; border-collapse: collapse;" Sodium chloride Sodium-chloride-3D-vdW.png General Systematic name Sodium chloride Other names Common salt,
halite,
table salt Molecular formula Na Cl Molar mass 58.44 g/mol Appearance White or colourless
solid or liquid CAS number ^* 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 Flash point Non-flammable R/S statement R: none
S: none RTECS number VZ4725000 Supplementary data page Structure and
properties n, ε_r, 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)
Chemical infobox

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the formula Na Cl. 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.

Crystal structure

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. The concentration of sodium ions in the blood is directly related to the regulation of safe body-fluid levels. Propagation of nerve impulses by signal transduction is regulated by sodium ions. (Potassium, a metal closely related to Sodium, is also a major component in the same bodily systems).

0.9% sodium chloride in water is called a physiological solution because it is isotonic with blood plasma. It is known medically as normal saline. Physiological solution is the mainstay of fluid replacement therapy that is widely used in medicine in prevention or treatment of dehydration, or as an intravenous therapy to prevent hypovolemic shock due to blood loss.

Humans are unusual among primates in secreting large amounts of salt by sweating.

Salt throughout 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.

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

In religion

There are thirty-two references to salt in the Bible, 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 "pure" 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).

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.

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 0853120277

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, particularly in colder climates where the required intake is much lower. This causes elevated levels of blood pressure 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 in to 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 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.

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

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