View source for Sodium chloride

{{short description|Chemical compound with formula NaCl}}
{{About|the chemical|its familiar form, common table salt|Salt|the medical solutions|Saline (medicine)|the mineral|Halite}}
{{Redirect|NaCl}}
{{Use dmy dates|date=November 2016}}
{{Chembox
|Verifiedfields = changed
|Watchedfields = changed
|verifiedrevid = 477002432
|ImageFile = Selpologne.jpg
|ImageCaption = Sodium chloride crystals in a form of [[halite]]
|ImageFile1 = NaCl bonds.svg
|ImageCaption1 = Crystal structure with sodium in purple and chloride in green<ref>{{cite web |url=https://physicsopenlab.org/2018/01/22/sodium-chloride-nacl-crystal/ |title=Sodium Chloride (NaCl) Crystal |publisher=PhysicsOpenLab |access-date=23 August 2021}}</ref>
|IUPACName = Sodium chloride
|OtherNames = {{unbulleted list
| common salt, regular salt
| halite, rock salt
| table salt, sea salt
| saline
}}
|Section1 = {{Chembox Identifiers
|CASNo = 7647-14-5
|CASNo_Ref = {{cascite|correct|CAS}}
|PubChem = 5234
|UNII = 451W47IQ8X
|UNII_Ref = {{fdacite|correct|FDA}}
|EINECS = 231-598-3
|KEGG = D02056
|KEGG_Ref = {{keggcite|correct|kegg}}
|MeSHName = Sodium+chloride
|ChEBI_Ref = {{ebicite|correct|EBI}}
|ChEBI = 26710
|ChEMBL = 1200574
|ChEMBL_Ref = {{ebicite|changed|EBI}}
|RTECS = VZ4725000
|Beilstein = 3534976
|Gmelin = 13673
|SMILES = [Na+].[Cl-]
|StdInChI = 1S/ClH.Na/h1H;/q;+1/p-1
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|InChI = 1/ClH.Na/h1H;/q;+1/p-1
|StdInChIKey = FAPWRFPIFSIZLT-UHFFFAOYSA-M
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|InChIKey = FAPWRFPIFSIZLT-REWHXWOFAE
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID = 5044
}}
|Section2 = {{Chembox Properties
|Formula = NaCl
|MolarMass = 58.443 g/mol<ref name="crc">Haynes, 4.89</ref>
|Appearance = Colorless cubic crystals<ref name=crc/>
|Odor = Odorless
|Density = 2.17 g/cm<sup>3</sup><ref name=crc/>
|MeltingPtC = 800.7
|MeltingPt_ref=<ref name=crc/>
|BoilingPtC = 1465
|BoilingPt_ref=<ref name=crc/>
|Solubility = 360 g/L (25°C)<ref name="crc"/>
|Solvent1 = ammonia
|Solubility1 = 21.5 g/L
|Solvent2 = methanol
|Solubility2 = 14.9 g/L
|RefractIndex = 1.5441 (at 589 nm)<ref>Haynes, 10.241</ref>
|MagSus = −30.2·10<sup>−6</sup> cm<sup>3</sup>/mol<ref>Haynes, 4.135</ref>
}}
|Section3 = {{Chembox Structure
|Structure_ref =<ref>Haynes, 4.148</ref>
|CrystalStruct = Face-centered cubic<br>(''see text''), [[Pearson symbol|cF8]]
|SpaceGroup = Fm{{overline|3}}m (No. 225)
|LattConst_a = 564.02 pm
|UnitCellFormulas = 4
|Coordination = octahedral at Na<sup>+</sup><br>octahedral at Cl<sup>−</sup>
}}
|Section4 = {{Chembox Thermochemistry
|Thermochemistry_ref =<ref>Haynes, 5.8</ref>
|DeltaHf = −411.120 kJ/mol
|Entropy = 72.10 J/(K·mol)
|HeatCapacity = 50.5 J/(K·mol)
}}
|Section5 = {{Chembox Pharmacology
|ATCCode_prefix = A12
|ATCCode_suffix = CA01
|ATC_Supplemental = {{ATC|B05|CB01}}, {{ATC|B05|XA03}}, {{ATC|S01|XA03}}
}}
|Section6 = {{Chembox Hazards
|NFPA-H = 0
|NFPA-F = 0
|NFPA-R = 0
|LD50 = 3 g/kg (oral, rats)<ref>[http://chem.sis.nlm.nih.gov/chemidplus/rn/7647-14-5 Sodium chloride]. nlm.nih.gov.</ref>
}}
|Section7 = {{Chembox Related
|OtherAnions = [[Sodium fluoride]]<br>[[Sodium bromide]]<br>[[Sodium iodide]]<br>[[Sodium astatide]]
|OtherCations = [[Lithium chloride]]<br>[[Potassium chloride]]<br>[[Rubidium chloride]]<br>[[Caesium chloride]]<br>[[Francium chloride]]
}}
}}

'''Sodium chloride''' {{IPAc-en|ˌ|s|oʊ|d|i|ə|m|_|ˈ|k|l|ɔr|aɪ|d}},<ref>{{Citation |last=Wells |first=John C. |title=Longman Pronunciation Dictionary |pages=143 and 755 |year=2008 |edition=3rd |publisher=Longman |isbn=9781405881180}}</ref> commonly known as [[Salt#Edible salt|table salt]], is an [[ionic compound]] with the [[chemical formula]] '''NaCl''', representing a 1:1 ratio of [[sodium]] and [[chloride]] ions. Sodium chloride is the [[salt (chemistry)|salt]] most responsible for the [[salinity]] of [[seawater]] and of the [[extracellular fluid]] of many [[multicellular organism]]s. In its edible form, salt (also known as ''table salt'') is commonly used as a [[condiment]] and [[curing (food preservation)|food preservative]]. Large quantities of sodium chloride are used in many industrial processes, and it is a major source of sodium and [[chlorine]] compounds used as [[feedstock]]s for further [[Chemical synthesis|chemical syntheses]]. Another major application of sodium chloride is [[deicing]] of roadways in sub-freezing weather.
{{TOC limit}}

==Uses==
In addition to the familiar domestic uses of salt, more dominant applications of the approximately 250 million tonnes per year production (2008 data) include chemicals and de-icing.<ref name="Ullmann">Westphal, Gisbert ''et al.'' (2002) "Sodium Chloride" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim {{doi|10.1002/14356007.a24_317.pub4}}.</ref>

===Chemical functions===
Salt is used, directly or indirectly, in the production of many chemicals, which consume most of the world's production.<ref name=usgs/>

====Chlor-alkali industry====
{{See also|Chloralkali process}}
It is the starting point for the [[chloralkali process]], the industrial process to produce [[chlorine]] and [[sodium hydroxide]], according to the [[chemical equation]]
:<chem>2 NaCl + 2 H2O ->[electrolysis] Cl2 + H2 + 2 NaOH</chem>

This electrolysis is conducted in either a mercury cell, a diaphragm cell, or a membrane cell. Each of those uses a different method to separate the chlorine from the sodium hydroxide. Other technologies are under development due to the high energy consumption of the electrolysis, whereby small improvements in the efficiency can have large economic paybacks. Some applications of chlorine include [[PVC]] [[thermoplastic]]s production, disinfectants, and solvents.

Sodium hydroxide is extensively used in many different industries enabling production of paper, soap, and aluminium etc.

===Soda-ash industry===
Sodium chloride is used in the [[Solvay process]] to produce [[sodium carbonate]] and [[calcium chloride]]. Sodium carbonate, in turn, is used to produce [[glass]], [[sodium bicarbonate]], and [[dye]]s, as well as a myriad of other chemicals. In the [[Mannheim process]], sodium chloride is used for the production of [[sodium sulfate]] and [[hydrochloric acid]].

===Standard===
Sodium chloride has an international standard that is created by [[ASTM International]]. The standard is named '''ASTM E534-13''' and is the standard test methods for chemical analysis of sodium chloride. These methods listed provide procedures for analyzing sodium chloride to determine whether it is suitable for its intended use and application.

===Miscellaneous industrial uses===
Sodium chloride is heavily used, so even relatively minor applications can consume massive quantities. In [[crude oil|oil]] and [[natural gas|gas]] exploration, salt is an important component of drilling fluids in well drilling. It is used to [[flocculation|flocculate]] and increase the [[density]] of the drilling fluid to overcome high downwell gas pressures. Whenever a drill hits a salt formation, salt is added to the drilling fluid to saturate the solution in order to minimize the dissolution within the salt stratum.<ref name=Ullmann/> Salt is also used to increase the curing of concrete in cemented casings.<ref name=usgs/>

In textiles and dyeing, salt is used as a brine rinse to separate organic contaminants, to promote "salting out" of dyestuff precipitates, and to blend with concentrated dyes to standardize{{clarify|date=October 2016}} them. One of its main roles is to provide the positive ion charge to promote the absorption of negatively charged ions of dyes.<ref name=usgs/>

It is also used in processing [[aluminium]], [[beryllium]], [[copper]], [[steel]], and [[vanadium]]. In the [[pulp and paper industry]], salt is used to bleach wood pulp. It also is used to make [[sodium chlorate]], which is added along with [[sulfuric acid]] and water to manufacture [[chlorine dioxide]], an excellent oxygen-based [[bleach]]ing chemical. The chlorine dioxide process, which originated in Germany after World War I, is becoming more popular because of environmental pressures to reduce or eliminate chlorinated bleaching compounds. In tanning and leather treatment, salt is added to animal [[hide (skin)|hides]] to inhibit microbial activity on the underside of the hides and to attract moisture back into the hides.<ref name=usgs/>

In rubber manufacture, salt is used to make [[synthetic rubber|buna]], [[neoprene]], and white rubber types. Salt brine and sulfuric acid are used to coagulate an emulsified [[latex]] made from chlorinated [[butadiene]].<ref name=usgs/><ref name=Ullmann/>

Salt also is added to secure the soil and to provide firmness to the foundation on which highways are built. The salt acts to minimize the effects of shifting caused in the subsurface by changes in humidity and traffic load.<ref name=usgs/>

Sodium chloride is sometimes used as a cheap and safe [[desiccant]] because of its [[hygroscopic]] properties, making [[salting (food)|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.

===Water softening===
[[Hard water]] contains calcium and magnesium ions that interfere with action of [[soap]] and contribute to the buildup of a scale or film of alkaline mineral deposits in household and industrial equipment and pipes. Commercial and residential water-softening units use [[ion-exchange resin]]s to remove ions that cause the hardness. These resins are generated and regenerated using sodium chloride.<ref name=usgs/><ref name=Ullmann/>

===Road salt===
The second major application of salt is for [[deicing]] and anti-icing of roads, both in [[grit bin]]s and spread by [[winter service vehicle]]s. In anticipation of snowfall, roads are optimally "anti-iced" with brine (concentrated [[solution (chemistry)|solution]] of salt in water), which prevents bonding between the snow-ice and the road surface. This procedure obviates the heavy use of salt after the snowfall. For de-icing, mixtures of brine and salt are used, sometimes with additional agents such as [[calcium chloride]] and/or [[magnesium chloride]]. The use of salt or brine becomes ineffective below {{convert|−10|°C|0}}.

[[File:Winter road salt.jpg|thumbnail|left|upright=1.15|Mounds of road salt for use in winter]]
Salt for de-icing in the United Kingdom predominantly comes from a single mine in [[Winsford]] in [[salt in Cheshire|Cheshire]]. Prior to distribution it is mixed with <100 ppm of [[sodium ferrocyanide]] as an [[anticaking agent]], which 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. Other additives had been used in road salt to reduce the total costs. For example, in the US, a byproduct carbohydrate solution from sugar-beet processing was mixed with rock salt and adhered to road surfaces about 40% better than loose rock salt alone. Because it stayed on the road longer, the treatment did not have to be repeated several times, saving time and money.<ref name=usgs/>

In the technical terms of physical chemistry, the minimum freezing point of a water-salt mixture is {{convert|−21.12|C|F}} for 23.31 wt% of salt. Freezing near this concentration is however so slow that the [[eutectic point]] of {{convert|−22.4|C|F}} can be reached with about 25 wt% of salt.<ref name="u1"/>

====Environmental effects====
Road salt ends up in fresh-water bodies and could harm aquatic plants and animals by disrupting their [[osmoregulation]] ability.<ref>{{cite news |last=Rastogi |first=Nina Shen |date=2010-02-16 |title=Salting the Earth |language=en-US |work=Slate |url=https://slate.com/technology/2010/02/does-road-salt-harm-the-environment.html |access-date=2023-03-11 |issn=1091-2339}}</ref> The omnipresence of salt in coastal areas poses a problem in any [[coating]] application, because trapped salts cause great problems in adhesion. Naval authorities and ship builders monitor the salt concentrations on surfaces during construction. Maximal salt concentrations on surfaces are dependent on the authority and application. The [[International Maritime Organization|IMO]] regulation is mostly used and sets salt levels to a maximum of 50&nbsp;mg/m<sup>2</sup> soluble salts measured as sodium chloride. These measurements are done by means of a [[Bresle test]]. Salinization (increasing salinity, aka ''[[freshwater salinization]] syndrome'') and subsequent increased metal leaching is an ongoing problem throughout North America and European fresh waterways.<ref>{{cite web |url=https://phys.org/news/2018-12-saltier-waterways-dangerous-chemical-cocktails.html |title=Saltier waterways are creating dangerous 'chemical cocktails' |website=phys.org}}</ref>

In highway de-icing, salt has been associated with [[corrosion]] of bridge decks, motor vehicles, reinforcement bar and wire, and unprotected steel structures used in road construction. [[Surface runoff]], vehicle spraying, and windblown salt also affect soil, roadside vegetation, and local surface water and groundwater supplies. Although evidence of environmental loading of salt has been found during peak usage, the spring rains and thaws usually dilute the concentrations of sodium in the area where salt was applied.<ref name=usgs/> A 2009 study found that approximately 70% of the road salt being applied in the [[Minneapolis-St Paul]] metro area is retained in the local watershed.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2009/02/090210125424.htm |title=Most Road Salt Is Making It into Lakes And Rivers |date=20 February 2009 |website=www.sciencedaily.com |publisher=University of Minnesota |access-date=27 September 2015}}</ref>

====Substitution====
Some agencies are substituting [[beer]], [[molasses]], and [[beet]] juice instead of [[road salt]].<ref>{{cite web |url=https://phys.org/news/2018-01-salt-solution-winter-dangers-threatens.html |author=Casey, Michael |title=Turning to beet juice and beer to address road salt danger |website=phys.org}}</ref> Airlines utilize more [[glycol]] and [[sugar]] rather than salt-based solutions for [[deicing]].<ref>{{cite web |url=https://www.mro-network.com/maintenance-repair-overhaul/easa-cautions-organic-salt-deicing-fluid |title=EASA Cautions on Organic Salt Deicing Fluid |date=9 December 2016 |website=MRO Network}}</ref>

===Food industry and agriculture===
{{main|Salt}}
Many [[microorganism]]s cannot live in a salty environment: water is drawn out of their [[cell (biology)|cells]] by [[osmosis]]. For this reason salt is used to [[food preservation|preserve]] some foods, such as bacon, fish, or cabbage.

Salt is added to food, either by the food producer or by the consumer, as a flavor enhancer, preservative, binder, [[fermentation (food)|fermentation]]-control additive, texture-control agent, and color developer. The salt consumption in the food industry is subdivided, in descending order of consumption, into other food processing, meat packers, [[canning]], baking, dairy, and grain mill products. Salt is added to promote color development in bacon, ham and other processed meat products. As a preservative, salt inhibits the growth of bacteria. Salt acts as a binder in [[sausage]]s to form a binding gel made up of meat, fat, and moisture. Salt also acts as a flavor enhancer and as a [[tenderizer]].<ref name=usgs/>

In many dairy industries, salt is added to cheese as a color-, fermentation-, and texture-control agent. The dairy subsector includes companies that manufacture creamery butter, condensed and evaporated milk, frozen desserts, ice cream, natural and processed cheese, and specialty dairy products. In canning, salt is primarily added as a flavor enhancer and [[preservative]]. It also is used as a carrier for other ingredients, dehydrating agent, enzyme inhibitor and tenderizer. In baking, salt is added to control the rate of fermentation in bread dough. It also is used to strengthen the [[gluten]] (the elastic protein-water complex in certain doughs) and as a flavor enhancer, such as a topping on baked goods. The food-processing category also contains grain mill products. These products consist of milling flour and rice and manufacturing cereal breakfast food and blended or prepared flour. Salt is also used a seasoning agent, e.g. in potato chips, [[pretzel]]s, and cat and dog food.<ref name=usgs/>

Sodium chloride is used in veterinary medicine as [[emesis]]-causing agent. It is given as warm saturated solution. Emesis can also be caused by [[pharynx|pharyngeal]] placement of small amount of plain salt or salt crystals.

===Medicine===
{{Main|Saline (medicine)}}
Sodium chloride is used together with water as one of the primary solutions for [[intravenous therapy]]. [[Nasal spray]] often contains a [[saline (medicine)|saline]] solution.

===Firefighting===
[[File:Metlx.jpg|thumb|upright|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 [[anticaking agent]]s (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 as a cartridge-operated unit, although stored pressure versions are now popular. Common sizes are {{convert|30|lb|kg}} portable and {{convert|350|lb|kg}} wheeled.{{citation needed|date=August 2020}}

===Cleanser===
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]], toothpaste, and popularly to de-ice driveways and patches of ice.

===Optical usage===
Defect-free NaCl crystals have an optical transmittance of about 90% for infrared light, specifically between 200&nbsp;[[nanometer|nm]] and 20&nbsp;[[µm]]. They were therefore used in optical components (windows and prisms) operating in that spectral range, where few non-absorbing alternatives exist and where requirements for absence of microscopic inhomogeneities are less strict than in the visible range. While inexpensive, NaCl crystals are soft and [[hygroscopy|hygroscopic]] – when exposed to the ambient air, they gradually cover with "frost". This limits application of NaCl to dry environments, vacuum-sealed assembly areas or for short-term uses such as prototyping. Nowadays materials like [[zinc selenide]] (ZnSe), which are stronger mechanically and are less sensitive to moisture, are used instead of NaCl for the infrared spectral range.

==Chemistry==

[[File:Natrium chloride kristal under microscope.jpg|thumb|Sodium chloride crystal under microscope.]]
[[File:NaCl octahedra.svg|thumb|NaCl octahedra. The yellow stipples represent the electrostatic force between the ions of opposite charge]]
===Solid sodium chloride===
{{See also|Cubic crystal system}}
In solid sodium chloride, each ion is surrounded by six ions of the opposite charge as expected on electrostatic grounds. The surrounding ions are located at the vertices of a regular [[octahedron]]. In the language of [[close-packing]], the larger [[chlorine|chloride]] [[ion]]s (167 pm in size<ref name="Shannon">{{cite journal |doi=10.1107/S0567739476001551 |title=Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides |author=R. D. Shannon |journal=Acta Crystallogr A |volume=32 |issue=5 |year=1976 |pages=751–767 |bibcode=1976AcCrA..32..751S |doi-access=}}</ref>) are arranged in a cubic array whereas the smaller [[sodium]] ions (116 pm<ref name=Shannon/>) fill all the cubic gaps (octahedral voids) between them. This same basic structure is found in many other [[chemical compound|compounds]] and is commonly known as the [[NaCl structure]] or rock salt crystal structure. It can be represented as a [[cubic crystal system|face-centered cubic]] (fcc) lattice with a two-atom basis or as two interpenetrating face centered cubic lattices. The first atom is located at each lattice point, and the second atom is located halfway between lattice points along the fcc unit cell edge.

Solid sodium chloride has a melting point of 801&nbsp;°C and liquid sodium chloride boils at 1465&nbsp;°C. Atomic-resolution real-time video imaging allows visualization of the initial stage of crystal nucleation of sodium chloride.<ref>{{cite journal |last1=Nakamuro |first1=Takayuki |last2=Sakakibara |first2=Masaya |last3=Nada |first3=Hiroki |last4=Harano |first4=Koji |last5=Nakamura |first5=Eiichi |year=2021 |title=Capturing the Moment of Emergence of Crystal Nucleus from Disorder |journal=Journal of the American Chemical Society |volume=143 |issue=4 |pages=1763–1767 |doi=10.1021/jacs.0c12100 |pmid=33475359 |doi-access=free}}</ref>

The [[Thermal conductivity]] of sodium chloride as a function of temperature has a maximum of 2.03&nbsp;W/(cm&nbsp;K) at {{convert|8|K}} and decreases to 0.069 at {{convert|314|K}}. It also decreases with [[doping (semiconductor)|doping]].<ref>{{cite book |last1=Sirdeshmukh |first1=Dinker B. |url=https://books.google.com/books?id=X-yL7EgMK6wC&pg=PA68 |title=Alkali halides: a handbook of physical properties |last2=Sirdeshmukh, Lalitha |last3=Subhadra, K. G. |publisher=Springer |year=2001 |isbn=978-3-540-42180-1 |pages=65, 68 |name-list-style=amp}}</ref>

[[File:NaCl(H2O)2slab.png|thumb|left|upright=1.25|View of one slab of [[hydrohalite]], NaCl·2H<sub>2</sub>O. (red = O, white = H, green = Cl, purple = Na).<ref>{{cite journal |last1=Klewe |first1=B |last2=Pedersen |year=1974 |title=The crystal structure of sodium chloride dihydrate |journal=Acta Crystallogr. |volume=B30 |issue=10 |pages=2363–2371 |doi=10.1107/S0567740874007138 |doi-access=}}</ref>]]
From cold (sub-freezing) solutions, salt crystallises with [[water of hydration]] as [[hydrohalite]] (the dihydrate NaCl·2{{Chem2|H2O}} NaCl·2H<sub>2</sub>O).<ref>Water-NaCl phase diagram. Lide, CRC Handbook of Chemistry and Physics, 86 ed (2005-2006), CRC pages 8-71, 8-116</ref>

In 2023, it was discovered that under pressure, sodium chloride can form the hydrates NaCl·8.5H<sub>2</sub>O and NaCl·13H<sub>2</sub>O.<ref>{{cite news |last1=University of Washington |title=Newly discovered form of salty ice could exist on surface of extraterrestrial moons |url=https://phys.org/news/2023-02-newly-salty-ice-surface-extraterrestrial.html |agency=Phys.org}}</ref>

{{Clear}}

===Aqueous solutions===
[[File:WatNaCl.png|thumb|right|upright=1.15|Phase diagram of water–NaCl mixture]]
The attraction between the Na<sup>+</sup> and Cl<sup>−</sup> ions in the solid is so strong that only highly [[polar solvent]]s like water dissolve NaCl well.

When dissolved in water, the sodium chloride framework disintegrates as the Na<sup>+</sup> and Cl<sup>−</sup> ions become surrounded by polar water molecules. These solutions consist of [[metal aquo complex]] with the formula [Na(H<sub>2</sub>O)<sub>8</sub>]<sup>+</sup>, with the Na–O distance of 250&nbsp;[[picometer|pm]]. The chloride ions are also strongly solvated, each being surrounded by an average of six molecules of water.<ref name="Lincoln">Lincoln, S. F.; Richens, D. T. and Sykes, A. G. (2003) "Metal Aqua Ions" Comprehensive Coordination Chemistry II Volume 1, pp. 515–555. {{doi|10.1016/B0-08-043748-6/01055-0}}.</ref> Solutions of sodium chloride have very different properties from pure water. The [[eutectic point]] is {{convert|−21.12|C|F}} for 23.31% [[mass fraction (chemistry)#Mass percentage|mass fraction]] of salt, and the boiling point of saturated salt solution is near {{convert|108.7|C|F}}.<ref name="u1">Elvers, B. ''et al.'' (ed.) (1991) ''Ullmann's Encyclopedia of Industrial Chemistry'', 5th ed. Vol. A24, Wiley, p. 319, {{ISBN|978-3-527-20124-2}}.</ref>

===pH of sodium chloride solutions===
The pH of a sodium chloride solution remains ≈7 due to the extremely weak basicity of the Cl<sup>−</sup> ion, which is the conjugate base of the strong acid HCl. In other words, NaCl has no effect on system pH<ref>{{cite web |url=https://www.flinnsci.com/api/library/Download/1f87f104ec4b4492a621f480797fbab1 |title=Acidic, Basic, and Neutral Salts |date=2016 |website=Flinn Scientific Chem Fax |access-date=18 September 2018 |quote=Neutralization of a strong acid and a strong base gives a neutral salt.}}</ref> in diluted solutions where the effects of ionic strength and activity coefficients are negligible.
{| class="wikitable" style="float:right; margin-left:1em;"
! {{Chemical datatable header}}|Solubility of NaCl<br>(g NaCl / 1&nbsp;kg of solvent at {{convert|25|C|F}})<ref>{{cite book |last=Burgess |first=J |title=Metal Ions in Solution |publisher=Ellis Horwood |year=1978 |isbn=978-0-85312-027-8 |location=New York}}</ref>
|-
| [[Water (molecule)|Water]] || 360
|-
| [[Formamide]] || 94
|-
| [[Glycerin]] || 83
|-
| [[Propylene glycol]] || 71
|-
| [[Formic acid]] || 52
|-
| Liquid [[ammonia]] || 30.2
|-
| [[Methanol]] || 14
|-
| [[Ethanol]] || 0.65
|-
| [[Dimethylformamide]] || 0.4
|-
| [[Propan-1-ol]] || 0.124
|-
| [[Sulfolane]] || 0.05
|-
| [[Butan-1-ol]] || 0.05
|-
| [[Propan-2-ol]] || 0.03
|-
| [[Pentan-1-ol]] || 0.018
|-
| [[Acetonitrile]] || 0.003
|-
| [[Acetone]] || 0.00042
|}

===Stoichiometric and structure variants===
Common salt has a 1:1 molar ratio of sodium and chlorine. In 2013, compounds of sodium and chloride of different [[stoichiometry|stoichiometries]] have been discovered; five new compounds were predicted (e.g., Na<sub>3</sub>Cl, Na<sub>2</sub>Cl, Na<sub>3</sub>Cl<sub>2</sub>, NaCl<sub>3</sub>, and NaCl<sub>7</sub>). The existence of some of them has been experimentally confirmed at high pressures and other conditions: cubic and orthorhombic NaCl<sub>3</sub>, two-dimensional metallic tetragonal Na<sub>3</sub>Cl and exotic hexagonal NaCl.<ref>{{cite journal |last1=Tikhomirova |first1=K. A. |last2=Tantardini |first2=C. |last3=Sukhanova |first3=E. V. |last4=Popov |first4=Z. I. |last5=Evlashin |first5=S. A. |last6=Tarkhov |first6=M. A. |last7=Zhdanov |first7=V. L. |year=2020 |title=Exotic Two-Dimensional Structure: The first case of Hexagonal NaCl |journal=The Journal of Physical Chemistry Letters |volume=11 |issue=10 |pages=3821–3827 |doi=10.1021/acs.jpclett.0c00874 |pmid=32330050 |s2cid=216130640 }}</ref> This indicates that compounds violating chemical intuition are possible, in simple systems under non-ambient conditions.<ref>{{cite journal |last1=Zhang |first1=W. |last2=Oganov |first2=A. R. |last3=Goncharov |first3=A. F. |last4=Zhu |first4=Q. |last5=Boulfelfel |first5=S. E. |last6=Lyakhov |first6=A. O. |last7=Stavrou |first7=E. |last8=Somayazulu |first8=M. |last9=Prakapenka |first9=V. B. |last10=Konôpková |first10=Z. |year=2013 |title=Unexpected Stable Stoichiometries of Sodium Chlorides |journal=Science |volume=342 |issue=6165 |pages=1502–1505 |arxiv=1310.7674 |bibcode=2013Sci...342.1502Z |doi=10.1126/science.1244989 |pmid=24357316 |s2cid=15298372 }}</ref>

==Occurrence==
Most of the world's salt is dissolved in the [[ocean]]{{citation needed|date=October 2022}}. A lesser amount is found in the [[Earth's crust]] as the water-soluble mineral [[halite]] (rock salt), and a tiny amount exists as suspended [[sea salt]] particles in the atmosphere{{citation needed|date=October 2022}}. These particles are the dominant [[cloud condensation nuclei]] far out at sea, which allow the formation of [[cloud]]s in otherwise [[pollution|non-polluted]] [[air]].<ref>{{cite journal |last=Mason |first=B. J. |date=2006 |title=The role of sea-salt particles as cloud condensation nuclei over the remote oceans |journal=Quarterly Journal of the Royal Meteorological Society |volume=127 |issue=576 |pages=2023–32 |bibcode=2001QJRMS.127.2023M |doi=10.1002/qj.49712757609 |s2cid=121846285}}</ref>

==Production==
Salt is currently [[Mass production|mass-produced]] by [[evaporation]] of [[seawater]] or [[brine]] from [[brine well]]s and [[salt lake (geography)|salt lakes]]. [[Salt mine|Mining]] of rock salt is also a major source. China is the world's main supplier of salt.<ref name="usgs">{{cite web|last=Kostick |first=Dennis S. |date=October 2010 |url=http://minerals.usgs.gov/minerals/pubs/commodity/salt/myb1-2008-salt.pdf |title=Salt |website=U.S. Geological Survey, 2008 Minerals Yearbook}}</ref> In 2017, world production was estimated at 280 million [[tonne]]s, the top five producers (in million tonnes) being China (68.0), United States (43.0), India (26.0), Germany (13.0), and Canada (13.0).<ref>{{cite web|url=https://minerals.usgs.gov/minerals/pubs/commodity/salt/mcs-2018-salt.pdf |title=Salt |website=U.S. Geological Survey, 2018 Mineral Commodity Summaries |first=Wallace P. |last=Bolen |date=January 2018}}</ref> Salt is also a byproduct of [[potassium]] mining.

<gallery mode="packed">
File:Salt mine 0096.jpg|Modern rock salt mine near [[Mount Morris (town), New York|Mount Morris]], [[New York (state)|New York]], [[United States]]
File:Dead-Sea---Salt-Evaporation-Ponds.jpg|[[Jordan]]ian and [[Israel]]i salt evaporation ponds at the south end of the [[Dead Sea]].
File:Piles of Salt Salar de Uyuni Bolivia Luca Galuzzi 2006 a.jpg|Mounds of salt, [[Salar de Uyuni]], [[Bolivia]].
</gallery>

==See also==
{{Portal|Chemistry}}
{{Colbegin}}
* [[Biosalinity]]
* [[Salt#Edible salt|Edible salt (table salt)]]
* [[Halite]], the mineral form of sodium chloride
* [[Health effects of salt]]
* [[Salinity]]
* [[Salting the earth]]
* [[Salt poisoning]]
{{Colend}}

==References==
{{Reflist}}
* {{USGS|title=Salt|url=http://minerals.usgs.gov/minerals/pubs/commodity/salt/myb1-2008-salt.pdf}}

==Cited sources==
* {{cite book |title=CRC Handbook of Chemistry and Physics |title-link=CRC Handbook of Chemistry and Physics |publisher=[[CRC Press]] |year=2011 |isbn=978-1439855119 |editor-last=Haynes |editor-first=William M. |edition=92nd}}

==External links==
{{Commons|NaCl}}
{{Cookbook|Salt}}
* [http://minerals.usgs.gov/minerals/pubs/commodity/salt/ Salt] [[United States Geological Survey]] Statistics and Information
* {{cite journal |date=December 1997 |title=Using Salt and Sand for Winter Road Maintenance |url=http://www.usroads.com/journals/p/rmj/9712/rm971202.htm |url-status=dead |journal=Road Management Journal |archive-url=https://web.archive.org/web/20160921160156/http://www.usroads.com/journals/p/rmj/9712/rm971202.htm |archive-date=21 September 2016 |access-date=13 February 2007}}
* Calculators: [http://www.aim.env.uea.ac.uk/aim/surftens/surftens.php surface tensions], and [http://www.aim.env.uea.ac.uk/aim/density/density_electrolyte.php densities, molarities and molalities] of aqueous NaCl (and other salts)
* [http://hazard.com/msds/mf/baker/baker/files/s3338.htm JtBaker MSDS]

{{Sodium compounds}}
{{Chlorides}}
{{Molecules detected in outer space}}
{{Authority control}}

[[Category:Alkali metal chlorides]]
[[Category:Chlorides]]
[[Category:Deliquescent substances]]
[[Category:Household chemicals]]
[[Category:Metal halides]]
[[Category:Ophthalmology drugs]]
[[Category:Rock salt crystal structure]]
[[Category:Sodium compounds]]