Everything about Sodium Chloride totally explained
» For sodium chloride in the diet, see salt.
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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 major ingredient in
edible salt, it's 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 grams of chlorine.
Production and use
Salt is currently mass 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).
As well as the familiar uses of salt in
cooking, salt is used in many applications, from
manufacturing pulp and paper to setting dyes in textiles and fabric, to producing
soaps and
detergents. In cold countries, 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). Sodium chloride is sometimes used as a cheap and safe
desiccant due to its
hygroscopic properties, making
salting an effective method of
food preservation historically. Even though more effective desiccants are available, few are safe for humans to ingest.
Image:Dead-Sea---Salt-Evaporation-Ponds.jpg| Israeli and Jordanian salt evaporation ponds at the south end of the Dead Sea
Image:Piles of Salt Salar de Uyuni Bolivia Luca Galuzzi 2006 a.jpg|Mounds of salt, Salar de Uyuni, Bolivia.
Image:Salt mine 0096.jpg|Modern rock salt mine near Mount Morris, New York.
Image:Aigues-Mortes2.jpg|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 + 2H
2O → Cl
2 + H
2 + 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's used for the production of
sodium sulfate and
hydrochloric acid.
Biological uses
Many
microorganisms can't 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.
Biological functions
In humans, a high-salt intake was demonstrated to attenuate Nitric Oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium
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.
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 can be represented as two interpenetrating face-centered cubic (fcc) lattices, or one fcc lattice with a two atom basis. It is most commonly known as the rocksalt crystal structure.
It is held together with an
ionic bond and
electrostatic forces.
Road salt
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. Adding salt to water will lower the freezing temperature of the water, depending on the concentration. The salinity (S) of water is measured as grams salt per kilogram (1000g) water, and the freezing temperatures are as follows.
| S(g/kg) |
0 |
10 |
20 |
24.7 |
30 |
35 |
| T(freezing) (C) |
0 |
-0.5 |
-1.08 |
-1.33 |
-1.63 |
-1.91 |
Additives
Table salt sold for consumption today isn't 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, to reduce the incidence of simple
goiter.
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 (CaCl
2). Both are similar and are effective in de-icing roads. When these chemicals are produced, they're 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 CaCl
2.
Further Information
Get more info on 'Sodium Chloride'.
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