Editing Chloride

{{short description|Main anion present in sea water}}
{{Distinguish|chlorine}}
{{other uses|Chloride (disambiguation)}}
{{Chembox
| Name = Chloride anion
| ImageFileL1 = Cl-.svg
| ImageSizeL1 = 50
| ImageFileR1 = Chloride_ion.svg
| ImageSizeR1 = 60px
| SystematicName = Chloride<ref>{{Cite web|url = https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=312|title = Chloride ion - PubChem Public Chemical Database|work = The PubChem Project|location = USA|publisher = National Center for Biotechnology Information}}</ref>
|Section1={{Chembox Identifiers
| IUPHAR_ligand = 2339
| CASNo = 16887-00-6
| CASNo_Ref = {{cascite|correct|CAS}}
| UNII = Q32ZN48698
| UNII_Ref = {{fdacite|correct|FDA}}
| PubChem = 312
| ChemSpiderID = 306
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| KEGG = C00698
| KEGG_Ref = {{keggcite|correct|kegg}}
| ChEBI = 17996
| ChEMBL = 19429
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| Beilstein = 3587171
| Gmelin = 14910
| SMILES = [Cl-]
| StdInChI = 1S/ClH/h1H/p-1
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = VEXZGXHMUGYJMC-UHFFFAOYSA-M
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
}}
|Section2={{Chembox Properties
| Formula = {{Chem2|Cl−}}
| Cl=1 
| ConjugateAcid = [[Hydrogen chloride]]
}}
|Section3={{Chembox Thermochemistry
| Entropy = 153.36&nbsp;J·K<sup>−1</sup>·mol<sup>−1</sup><ref name=b1>{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A21}}</ref>
| DeltaHf = −167&nbsp;kJ·mol<sup>−1</sup><ref name=b1 />
}}
|Section4={{Chembox Related
| OtherAnions = {{ubl|[[Fluoride]]|[[Bromide]]|[[Iodide]]}}
}}
}}

The term '''chloride''' refers to a compound or molecule that contains either a [[chlorine]] [[anion]] ({{chem2|Cl−|auto=1}}), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a [[single bond]] ({{chem2|\sCl}}). The pronunciation of the word "chloride" is {{IPAc-en|ˈ|k|l|ɔər|aɪ|d}}.<ref>{{citation|last=Wells|first=John C.|year=2008|title=Longman Pronunciation Dictionary|edition=3rd|publisher=Longman|page=143|isbn=9781405881180}}</ref>

Chloride [[Salt (chemistry)|salts]] such as [[sodium chloride]] are often soluble in water.<ref name="auto">Green, John, and Sadru Damji. "Chapter 3." ''Chemistry''. Camberwell, Vic.: IBID, 2001. Print.</ref> It is an essential [[electrolyte]] located in all body fluids responsible for maintaining acid/base balance, transmitting [[nerve impulses]] and regulating liquid flow in and out of cells. Other examples of ionic chlorides include [[potassium chloride]] ({{chem2|KCl}}), [[calcium chloride]] ({{chem2|CaCl2}}), and [[ammonium chloride]] ({{chem2|NH4Cl}}). Examples of covalent chlorides include [[methyl chloride]] ({{chem2|CH3Cl}}), [[carbon tetrachloride]] ({{chem2|CCl4}}), [[sulfuryl chloride]] ({{chem2|SO2Cl2}}), and [[monochloramine]] ({{chem2|NH2Cl}}).

==Electronic properties==
A chloride ion (diameter 167&nbsp;[[picometre|pm]]) is much larger than a chlorine atom (diameter 99&nbsp;pm). The chlorine atom's hold on the valence shell is weaker because the chloride anion has one more electron than it does.<ref>{{Cite web |title=Size of Atoms |url=http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch7/size.html |access-date=2022-03-03 |website=chemed.chem.purdue.edu}}</ref> The ion is colorless and diamagnetic. In aqueous solution, it is highly soluble in most cases; however, for some chloride salts, such as [[silver chloride]], [[lead(II) chloride]], and [[mercury(I) chloride]], they are only slightly soluble in water.<ref>{{cite book|last1=Zumdahl|first1=Steven|title=Chemical Principles|date=2013|publisher=Cengage Learning|isbn=978-1-285-13370-6|pages=109|edition=7th}}<!--|access-date=24 April 2015--></ref> In aqueous solution, chloride is bonded by the protic end of the water molecules.

==Reactions of chloride==
Chloride can be oxidized but not reduced. The first oxidation, as employed in the chlor-alkali process, is conversion to chlorine gas. Chlorine can be further oxidized to other oxides and oxyanions including [[hypochlorite]] (ClO<sup>−</sup>, the active ingredient in chlorine [[bleach]]), [[chlorine dioxide]] (ClO<sub>2</sub>), [[chlorate]] ({{chem|ClO|3|−}}), and [[perchlorate]] ({{chem|ClO|4|−}}).

In terms of its acid–base properties, chloride is a [[weak base]] as indicated by the negative value of the [[pKa|p''K''<sub>a</sub>]] of hydrochloric acid. Chloride can be protonated by [[strong acid]]s, such as sulfuric acid:
:NaCl + H<sub>2</sub>SO<sub>4</sub> → NaHSO<sub>4</sub> + HCl

Ionic chloride salts react with other salts to exchange anions. The presence of halide ions like chloride can be detected using [[silver nitrate]]. A solution containing chloride ions will produce a white [[silver chloride]] precipitate:<ref>{{Cite web |title=Testing for halide ions - Group 0 and testing ions - GCSE Chemistry (Single Science) Revision - WJEC |url=https://www.bbc.co.uk/bitesize/guides/zm426yc/revision/2 |access-date=2022-03-03 |website=BBC Bitesize |language=en-GB}}</ref>
:Cl<sup>−</sup> + Ag<sup>+</sup> → AgCl

The concentration of chloride in an assay can be determined using a [[chloridometer]], which detects silver ions once all chloride in the assay has precipitated via this reaction.

[[Silver chloride electrode|Chlorided silver electrodes]] are commonly used in {{Lang|la|ex vivo}} [[electrophysiology]].<ref>Molleman, Areles (2003). "Patch Clamping: An Introductory Guide to Patch Clamp Electrophysiology". Wiley & Sons. {{ISBN|978-0-471-48685-5}}.</ref>

==Other oxyanions==
Chlorine can assume [[oxidation state]]s of −1, +1, +3, +5, or +7. Several neutral [[chlorine oxide]]s are also known.

:{| class="wikitable"
|-
! Chlorine oxidation state
| −1
| +1
| +3
| +5
| +7
|-
! Name
| '''chloride'''
| [[hypochlorite]]
| [[chlorite]]
| [[chlorate]]
| [[perchlorate]]
|-
! Formula
| Cl<sup>−</sup>
| ClO<sup>−</sup>
| {{chem|ClO|2|−}}
| {{chem|ClO|3|−}}
| {{chem|ClO|4|−}}
|-
! Structure
| [[File:Chloride-ion-3D-vdW.png|50px|The chloride ion]]
| [[File:Hypochlorite-3D-vdW.png|50px|The hypochlorite ion]]
| [[File:Chlorite-3D-vdW.png|50px|The chlorite ion]]
| [[File:Chlorate-3D-vdW.png|50px|The chlorate ion]]
| [[File:Perchlorate-3D-vdW.png|50px|The perchlorate ion]]
|}

==Occurrence in nature==
In nature, chloride is found primarily in seawater, which has a chloride ion concentration of 19400&nbsp;mg/liter.<ref>{{Cite web|title=Chloride and Salinity|url=https://www.ldeo.columbia.edu/edu/k12/snapshotday/activities/2011/Classroom%20HS%20activity/chloride%20conversion/Chloride%20and%20Salinity.pdf|date=8 September 2011|access-date=8 January 2023|website=colombia.edu}}</ref> Smaller quantities, though at higher concentrations, occur in certain inland seas and in subterranean [[brine well]]s, such as the [[Great Salt Lake]] in [[Utah]] and the [[Dead Sea]] in Israel.<ref>{{cite book |last1=Greenwood |first1=N. N. |title=Chemistry of the elements |date=1984 |publisher=Pergamon Press |location=Oxford [Oxfordshire] |isbn=9780750628327 |edition=1st}}</ref> 
Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. Some chloride-containing minerals include [[halite]] (sodium chloride [[NaCl]]), [[sylvite]] (potassium chloride [[KCl]]), [[bischofite]] (MgCl<sub>2</sub>∙6H<sub>2</sub>O), [[carnallite]] (KCl∙MgCl<sub>2</sub>∙6H<sub>2</sub>O), and [[kainite]] (KCl∙MgSO<sub>4</sub>∙3H<sub>2</sub>O). It is also found in evaporite minerals such as [[chlorapatite]] and [[sodalite]].

===Role in biology===
Chloride has a major physiological significance,<ref>{{Cite journal|title=Chloride ions in health and disease|journal=Bioscience Reports|last1=Raut|first1=Satish|volume=44|issue=5|doi=10.1042/BSR20240029
|year=2024|at=BSR20240029|language=en|pmc=11065649|pmid=38573803}}</ref> which includes regulation of [[osmotic pressure]], electrolyte balance and acid-base homeostasis. Chloride is present in all [[body fluid]]s,<ref>{{Cite journal|title=The distribution of total body chloride in man|journal=Journal of Clinical Investigation|last1=Deane|first1=Norman|volume=31|last2=Ziff|first2=Morris|issue=2|doi=10.1172/JCI102592|year=1952|at=p. 201, Table 1|language=en|pmc=436401|pmid=14907900|last3=Smith|first3=Homer W.}}</ref> and is the most abundant extracellular [[anion]] which accounts for around one third of [[extracellular fluid]]'s [[tonicity]].<ref>{{cite journal |last1=Berend |first1=Kenrick |last2=van Hulsteijn |first2=Leonard Hendrik |last3=Gans |first3=Rijk O.B. |title=Chloride: The queen of electrolytes? |journal=European Journal of Internal Medicine |date=April 2012 |volume=23 |issue=3 |pages=203–211 |doi=10.1016/j.ejim.2011.11.013 |pmid=22385875}}</ref><ref>{{cite journal |last1=Rein |first1=Joshua L. |last2=Coca |first2=Steven G. |title="I don't get no respect": the role of chloride in acute kidney injury |journal=American Journal of Physiology. Renal Physiology |date=1 March 2019 |volume=316 |issue=3 |pages=F587–F605 |doi=10.1152/ajprenal.00130.2018 |pmid=30539650 |issn=1931-857X |pmc=6459301}}</ref>

Chloride is an essential [[Electrolyte#Physiological importance|electrolyte]], playing a key role in maintaining cell [[Homeostasis#Overview|homeostasis]] and transmitting [[action potentials]] in neurons.<ref>{{cite journal |title=Molecular Structure and Physiological Function of Chloride Channels |url=http://physrev.physiology.org/content/82/2/503 |journal=Physiological Reviews |date=2002-04-01 |issn=0031-9333 |pmid=11917096 |pages=503–568 |volume=82 |issue=2 |doi=10.1152/physrev.00029.2001 |first1=Thomas J. |last1=Jentsch |first2=Valentin |last2=Stein |first3=Frank |last3=Weinreich |first4=Anselm A. |last4=Zdebik}}</ref> It can flow through [[chloride channels]] (including the [[GABAA|GABA<sub>A</sub>]] receptor) and is transported by [[KCC2]] and [[NKCC2]] transporters.

Chloride is usually (though not always) at a higher extracellular concentration, causing it to have a negative [[reversal potential]] (around −61&nbsp;mV at 37&nbsp;°C in a mammalian cell).<ref>{{cite web |title=Equilibrium potentials |url=http://www.d.umn.edu/~jfitzake/Lectures/DMED/IonChannelPhysiology/MembranePotentials/EquilibriumPotentials.html |website=www.d.umn.edu}}</ref> Characteristic concentrations of chloride in model organisms are: in both ''E. coli'' and budding yeast are 10–200&nbsp;[[molar concentration|mM]] (dependent on medium), in mammalian cells 5–100&nbsp;mM and in [[blood plasma]] 100&nbsp;mM.<ref>{{cite web|url = http://book.bionumbers.org/what-are-the-concentrations-of-different-ions-in-cells/|title =Cell Biology by the Numbers: What are the concentrations of different ions in cells? |website =book.bionumbers.org|first1= Ron|last1= Milo|first2= Rob |last2=Philips|access-date=24 March 2017}}</ref>

Chloride is also needed for the production of [[hydrochloric acid]] in the stomach.<ref>{{cite web|url=http://www.med.umich.edu/1libr/aha/aha_schlorid_crs.htm |access-date=30 April 2010 |url-status=dead |archive-url=https://web.archive.org/web/20090331211149/http://med.umich.edu/1libr/aha/aha_schlorid_crs.htm |archive-date=31 March 2009 |title=Blood (Serum) Chloride Level Test}}</ref>

The concentration of chloride in the blood is called [[serum chloride]], and this concentration is regulated by the [[kidneys]]. A chloride ion is a structural component of some proteins; for example, it is present in the [[amylase]] enzyme. For these roles, chloride is one of the essential [[dietary mineral]]s (listed by its element name ''chlorine''). [[Serum (blood)|Serum]] chloride levels are mainly regulated by the kidneys through a variety of transporters that are present along the [[nephron]].<ref>{{cite journal |last1=Nagami |first1=Glenn T. |title=Hyperchloremia – Why and how |journal=Nefrología (English Edition) |date=1 July 2016 |volume=36 |issue=4 |pages=347–353 |doi=10.1016/j.nefro.2016.04.001 |pmid=27267918 |url=https://www.revistanefrologia.com/en-hyperchloremia-why-how-articulo-S021169951630025X |language=en |issn=2013-2514|doi-access=free }}</ref> Most of the chloride, which is filtered by the [[Glomerulus (kidney)|glomerulus]], is reabsorbed by both [[Proximal tubule|proximal]] and [[distal tubule]]s (majorly by proximal tubule) by both active and passive transport.<ref>{{cite journal |last1=Shrimanker |first1=Isha |last2=Bhattarai |first2=Sandeep |title=Electrolytes |url=https://pubmed.ncbi.nlm.nih.gov/31082167/ |website=StatPearls |publisher=StatPearls Publishing |date=2020|pmid=31082167 }}</ref>

===Corrosion===
[[Image:NaCl polyhedra.png|thumb|right|The structure of sodium chloride, revealing the tendency of chloride ions (green spheres<!--even though both spheres are equiv-->) to link to several cations.]]
The presence of chlorides, such as in seawater, significantly worsens the conditions for [[pitting corrosion]] of most metals (including stainless steels, aluminum and high-alloyed materials). Chloride-induced corrosion of steel in concrete leads to a local breakdown of the protective oxide form in alkaline concrete, so that a subsequent localized corrosion attack takes place.<ref>{{cite book |last1=Criado |first1=M. |title=Handbook of Alkali-Activated Cements, Mortars and Concretes |publisher=Woodhead Publishing |isbn=978-1-78242-276-1 |pages=333–372 |chapter-url=https://www.sciencedirect.com/science/article/pii/B9781782422761500137 |language=en |chapter=13. The corrosion behaviour of reinforced steel embedded in alkali-activated mortar|date=January 2015 |doi=10.1533/9781782422884.3.333 }}</ref>

===Environmental threats===
Increased concentrations of chloride can cause a number of ecological effects in both aquatic and terrestrial environments. It may contribute to the acidification of streams, mobilize radioactive soil metals by ion exchange, affect the mortality and reproduction of aquatic plants and animals, promote the invasion of saltwater organisms into previously freshwater environments, and interfere with the natural mixing of lakes. Sodium chloride has been shown to change the composition of microbial species at relatively low concentrations, hinder the [[denitrification]] process, a microbial process essential to [[nitrate]] removal and the conservation of water quality, and inhibit the [[nitrification]] and respiration of organic matter.<ref>{{cite book |last1=Kaushal |first1=S. S. |title=Encyclopedia of Inland Waters |publisher=Academic Press |isbn=978-0-12-370626-3 |pages=23–29 |language=en |chapter=Chloride|date=19 March 2009 }}</ref>

==Production==
The [[chlor-alkali]] industry is a major consumer of the world's energy budget. This process converts concentrated sodium chloride solutions into chlorine and sodium hydroxide, which are used to make many other materials and chemicals. The process involves two parallel reactions:
:2&nbsp;Cl<sup>−</sup> → {{chem|Cl|2}} + 2&nbsp;[[electron|e<sup>−</sup>]]
:2&nbsp;{{chem|H|2|O}} + 2&nbsp;e<sup>−</sup> → H<sub>2</sub> + 2&nbsp;OH<sup>−</sup>
[[Image:Chloralkali membrane.svg|thumb|center|600px|Basic membrane cell used in the [[electrolysis]] of brine. At the anode ('''A'''), chloride (Cl<sup>−</sup>) is oxidized to chlorine. The ion-selective membrane ('''B''') allows the counterion Na<sup>+</sup> to freely flow across, but prevents anions such as hydroxide (OH<sup>−</sup>) and chloride from diffusing across. At the cathode ('''C'''), water is reduced to hydroxide and hydrogen gas.]]

==Examples and uses==
An example is table salt, which is [[sodium chloride]] with the [[chemical formula]] NaCl. In [[water (molecule)|water]], it dissociates into Na<sup>+</sup> and Cl<sup>&minus;</sup> ions. Salts such as [[calcium chloride]], [[magnesium chloride]], [[potassium chloride]] have varied uses ranging from medical treatments to cement formation.<ref name="auto"/>

Calcium chloride (CaCl<sub>2</sub>) is a salt that is marketed in [[Granular material|pellet]] form for removing dampness from rooms. Calcium chloride is also used for maintaining unpaved roads and for fortifying roadbases for new construction. In addition, calcium chloride is widely used as a [[de-icer]], since it is effective in lowering the [[melting point]] when applied to ice.<ref>{{Cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/saltcom.html|title=Common Salts|website=hyperphysics.phy-astr.gsu.edu|publisher=Georgia State University}}</ref>

Examples of [[Covalent bonding|covalently-bonded]] chlorides are [[phosphorus trichloride]], [[phosphorus pentachloride]], and [[thionyl chloride]], all three of which are reactive chlorinating [[reagent]]s.

===Water quality and processing===
A major application involving chloride is [[desalination]], which involves the energy intensive removal of chloride salts to give [[drinking water|potable water]]. In the [[petroleum industry]], the chlorides are a closely monitored constituent of the [[drilling fluid|mud system]]. An increase of the chlorides in the mud system may be an indication of drilling into a high-pressure saltwater formation. Its increase can also indicate the poor quality of a target sand.{{Citation needed|date=March 2012}}

Chloride is also a useful and reliable chemical indicator of river and groundwater fecal contamination, as chloride is a non-reactive solute and ubiquitous to sewage and potable water. Many water regulating companies around the world utilize chloride to check the contamination levels of the rivers and potable water sources.<ref>{{cite web|url=http://www.gopetsamerica.com/substance/chlorides.aspx|title=Chlorides|website=www.gopetsamerica.com|access-date=14 April 2018|archive-url=https://web.archive.org/web/20160818142707/http://www.gopetsamerica.com/substance/chlorides.aspx|archive-date=18 August 2016|url-status=dead}}</ref>

===Food===
Chloride salts such as [[sodium chloride]] are used to [[Salting (food)|preserve food]] and as nutrients or [[condiment]]s.

== See also ==
* [[Halide]]
* [[Renal chloride reabsorption]]

== References ==
{{Reflist}}

{{Chlorides}}
{{Monatomic anion compounds}}

{{Authority control}}

[[Category:Anions]]
[[Category:Chlorides| ]]
[[Category:Leaving groups]]
[[Category:Dietary minerals]]