Sodium chloride
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.
Encyclopedia
| 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 |
| Melting point | 801 °C |
| Boiling point | 1465 °C |
| 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, er, 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
|
|
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.
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 .
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. .
0.9% sodium chloride in
water is called a
physiological solutionbecause 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-five 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 . 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 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 .
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.
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 : the ions prevent regular ice crystals from forming . 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
...
, 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.
- 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
External links
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Statistics and Information
