Sodium chloride

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This article is about the chemical compound. For sodium chloride in the diet, see Salt. For sodium chloride as a mineral, see Halite.

| Coordination
geometry

Sodium chloride
File:Sodiumchloride crystal 01.jpg
File:Sodium-chloride-3D-ionic.png
IUPAC name Sodium chloride
Other names Common salt, halite, table salt, rock salt, saline, hyposaline, sodium monochloride, sodium chloric, saltex
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	7647-14-5 Y
PubChem	5234
ChemSpider	5044
RTECS number	VZ4725000
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	NaCl
Molar mass	58.443 g/mol
Appearance	Colorless/white crystalline solid
Odor	Odorless
Density	2.165 g/cm3
Melting point	801 °C, 1074 K, 1474 °F
Boiling point	1413 °C, 1686 K, 2575 °F
Solubility in water	356 g/L (0 °C) 359 g/L (25 °C) 391 g/L (100 °C)
Solubility	soluble in glycerol, ethylene glycol, formic acid insoluble in HCl
Solubility in methanol	14.9 g/L
Solubility in ammonia	21.5 g/L
Acidity (pKa)	6.7–7.3
Refractive index (nD)	1.5442 (589 nm)
style="background: #F8EABA; text-align: center;" colspan="2" | Structure
Crystal structure	Face-centered cubic (see text), cF8
Space group	Fm3m, No. 225
Lattice constant	a = 564.02 pm
Octahedral (Na+) Octahedral (Cl–)
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
EU Index	Not listed
NFPA 704	75px 0 0 0
Flash point	Non-flammable
LD50	3000–8000 mg/kg (oral in rats, mice, rabbits)
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Other anions	Sodium fluoride Sodium bromide Sodium iodide
Other cations	Lithium chloride Potassium chloride Rubidium chloride Caesium chloride
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium chloride, also known as salt, common salt, table salt, or halite, is an ionic 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 is commonly used as a condiment and food preservative.

Properties

Thermal conductivity of pure NaCl as a function of temperature has a maximum of 2.03 W/(cm K) at 8 K and decreases to 0.069 at 314 K (41 °C). It also decreases with doping.

Production and use

File:Salt mine 0096.jpg

Modern rock salt mine near Mount Morris, New York, United States

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 2009, world production was estimated at 260 million metric tons, the top five producers (in million tonnes) being China (60.0), United States (46.0), Germany (16.5), India (15.8) and Canada (14.0).

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, detergents, and other bath products. It is the major source of industrial chlorine and sodium hydroxide, and used in almost every industry.

Sodium chloride is sometimes used as a cheap and safe desiccant because it appears to have hygroscopic properties, making salting an effective method of food preservation historically; the salt draws water out of bacteria through osmotic pressure, keeping it from reproducing, a major source of food spoilage. Even though more effective desiccants are available, few are safe for humans to ingest.

style="background: #F8EABA; text-align: center;" colspan="2"|Solubility of NaCl in various solvents (g NaCl / 1 kg of solvent at 25 °C)
H2O	360
Liquid ammonia	30.2
glycerin	83
propylene glycol	71
Methanol	14
Ethanol	0.65
1-propanol	0.124
2-propanol	0.03
1-butanol	0.05
1-pentanol	0.018
Sulfolane	0.05
Formic acid	52
Acetone	0.00042
Formamide	94
Acetonitrile	0.003
Dimethylformamide	0.4

Synthetic uses

Uses of chlorine include PVC, pesticides and epoxy resins. 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 now 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 is used for the production of sodium sulfate and hydrochloric acid.

Biological uses

Many micro organisms 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 can also be used to detach leeches that have attached themselves to feed. It is also used to disinfect wounds.

Optical uses

Pure NaCl crystal is an optical compound with a wide transmission range from 200 nm to 20 µm. It was often used in the infrared spectrum range and it is still used sometimes.

While inexpensive, NaCl crystal is soft and hygroscopic. When exposed to free air, NaCl optics gradually covers with "frost". This limits application of NaCl to protected environments or for short-term uses such as prototyping.

Today tougher crystals like zinc selenide (ZnSe) are used instead of NaCl (for the IR spectral range).

Optical data

• Transmitivity: 92% (from 400 nm to 13 μm)
• Refractive Index: 1.494 at 10 μm
• Reflection Loss: 7.5% at 10 μm (2 surfaces)
• dN/dT: −36.2×10⁻⁶/°C at 0.7 μm

Household uses

Since at least medieval times, people have used salt as a cleansing agent rubbed on household surfaces. It is also used in many brands of shampoo, and popularly to de-ice driveways and patches of ice.

Firefighting uses

File:Metlx.jpg

A class D fire extinguisher for various metals

Sodium chloride is the principal extinguishing agent in fire extinguishers (Met-L-X, Super D) used on combustible metal fires such as magnesium, potassium, sodium, and NaK alloys (Class D). Thermoplastic powder is added to the mixture, along with waterproofing (metal stearates) and anti-caking materials (tricalcium phosphate) to form the extinguishing agent. When it is applied to the fire, the salt acts like a heat sink, dissipating heat from the fire, and also forms an oxygen-excluding crust to smother the fire. The plastic additive melts and helps the crust maintain its integrity until the burning metal cools below its ignition temperature. This type of extinguisher was invented in the late 1940s in the cartridge-operated type shown here, although stored pressure versions are now popular. Common sizes are 30 lb. portable and 350 lb. wheeled.

In weather

File:Clouds from above.JPG

Clouds above the Pacific

Small particles of sea salt are the dominant cloud condensation nuclei well out at sea, which allow the formation of clouds in otherwise non-polluted air. Snow removal by addition of salt (salting) is done to make travel easier and safer, and decrease the long term impact of a heavy snowfall on human populations. This process is done by both individual households and by governments and institutions and utilizes salts to eliminate snow from road surfaces and sidewalks.

Biological functions

For further information about sodium chloride in the diet, see Salt.

In humans, a high-salt intake has long been suspected to generally raise blood pressure. More recently, it 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

File:NaCl polyhedra.png

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

File:Close Up View Of Sodium Chloride Crystals.jpg

Close up view of NaCl crystals

Main article: Cubic crystal system

Sodium chloride forms crystals with face-centered 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 silver spheres, fill all the cubic gaps between them. Each ion is surrounded by six ions of the other kind; the surrounding ions are located at the vertices of a regular octahedron.

This same basic structure is found in many other minerals and is commonly known as the halite or rock-salt crystal structure. It can be represented as a face-centered cubic (fcc) lattice with a two atom basis. The first atom is located at each lattice point, and the second atom is located half way between lattice points along the fcc unit cell edge.

It is held together by an ionic bond which is produced by electrostatic forces arising from the difference in charge between the ions.

Road salt

While salt was once a scarce commodity in history, industrialized production has now made salt plentiful. Approximately 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. Calcium chloride is preferred over sodium chloride, since CaCl₂ releases energy upon forming a solution with water, heating any ice or snow it is in contact with. It also lowers the freezing point, depending on the concentration. NaCl does not release heat upon solution; however, it does lower the freezing point. Calcium chloride is thought to be more environmentally friendly than sodium chloride when used to de-ice roads, however a drawback is that it tends to promote corrosion (of vehicles) more so than sodium chloride. NaCl is also more readily available and does not have any special handling or storage requirements, unlike calcium chloride. The salinity (S) of water is measured as grams salt per kilogram of water, and the freezing temperatures are as follows.

S (g/kg)	0	15	30	45	59	75	90	106	123	140	157	175	193	212	231	250	269	290	311	331	353
T (°C)	0	−0.8	−1.7	−2.7	−3.6	−4.6	−5.5	−6.6	−7.8	−9.1	−10.4	−11.8	−13.2	−14.6	−16.2	−17.8	−19.4	−21.1	−17.3	−11.1	−2.7

Additives

Most table 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, to reduce the incidence of simple goiter.

Salt for de-icing in the United Kingdom predominantly comes from a single mine in Winsford in Cheshire. Prior to distribution it has an anti-caking agent added: sodium hexacyanoferrate(II) at less than 100 ppm. This treatment enables rock salt to flow freely out of the gritting vehicles despite being stockpiled prior to use. In recent years this additive has also been used in table salt.

Environmental impact

Road salt ends up in fresh water bodies and could harm aquatic plants and animals by disrupting their osmoregulation ability. An alternative is to spread rough sand on ice so the surface is not slippery.

The omnipresence of salt posts a problem in any coastal coating application, as trapped salts cause great problems in adhesion. Costs can reach staggering amounts. Naval authorities and ship builders keep a close eye on salt concentrations on surfaces during construction. Maximum salt concentrations on surfaces are dependent on the authority and application. The IMO regulation is mostly used and sets salt levels to a maximum of 50 mg/m² soluble salts measured as sodium chloride. These measurements are done by means of a Bresle test.

• Dead-Sea---Salt-Evaporation-Ponds.jpg

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

• Piles of Salt Salar de Uyuni Bolivia Luca Galuzzi 2006 a.jpg

  Mounds of salt, Salar de Uyuni, Bolivia.

• Aigues-Mortes2.jpg

  Evaporation lagoons, Aigues-Mortes, France.

See also

• Biosalinity
• Kala Namak
• Halite, the mineral form of sodium chloride
• Salinity
• Salt
• Soap
• Salting the earth

External links

• The Salt Manufacturers Association website
• Salt Institute website
• Salt Archive website
• Salt United States Geological Survey Statistics and Information
• US Road Management website
• Salt Intake in Cold Weather
• Oxford MSDS
• JtBaker MSDS

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