Last updated
Chloride ion.svg
Systematic IUPAC name
Chloride [1]
  • 16887-00-6 Yes check.svgY
3D model (JSmol)
PubChem CID
  • InChI=1S/ClH/h1H/p-1 Yes check.svgY
  • [Cl-]
Molar mass 35.45 g·mol−1
Conjugate acid Hydrogen chloride
153.36 J·K−1·mol−1 [2]
−167 kJ·mol−1 [2]
Related compounds
Other anions


Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

The chloride ion /ˈklɔːrd/ [3] is the anion (negatively charged ion) Cl. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts such as sodium chloride are often very soluble in water. [4] It is an essential electrolyte located in all body liquids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating liquid flow in and out of cells. Less frequently, the word chloride may also form part of the "common" name of chemical compounds in which one or more chlorine atoms are covalently bonded. For example, methyl chloride, with the standard name chloromethane (see IUPAC books) is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion.


Electronic properties

A chloride ion (diameter 167  pm) is much larger than a chlorine atom (diameter 99 pm), respectively. 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. [5] In aqueous solution, chloride is bound 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, the active ingredient in chlorine bleach), chlorine dioxide (ClO2), chlorate (ClO
), and perchlorate (ClO

In terms of its acid–base properties, chloride is a very weak base as indicated by the negative value of the pKa of hydrochloric acid. Chloride can be protonated by strong acids, such as sulfuric acid:

NaCl + H2SO4 → NaHSO4 + HCl

Ionic chloride salts reaction with other salts to exchange anions. The presence of chloride is often detected by its formation of an insoluble silver chloride upon treatment with silver(I) ions:

Cl + Ag+ → 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.

Chlorided silver electrodes are commonly used in ex vivo electrophysiology. [6]

Other oxyanions

Chlorine can assume oxidation states of −1, +1, +3, +5, or +7. Several neutral chlorine oxides are also known.

Chlorine oxidation state−1+1+3+5+7
Namechloride hypochlorite chlorite chlorate perchlorate
Structure Chloride-ion-3D-vdW.png Hypochlorite-3D-vdW.png Chlorite-3D-vdW.png Chlorate-3D-vdW.png Perchlorate-3D-vdW.png

Occurrence in nature

In nature, chloride is found primarily in seawater, which contains 1.94%[ clarification needed ] chloride. Smaller quantities, though at higher concentrations, occur in certain inland seas and in subterranean brine wells, such as the Great Salt Lake in Utah and the Dead Sea in Israel. [7] 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 (MgCl2∙6H2O), carnallite (KCl∙MgCl2∙6H2O), and kainite (KCl∙MgSO4∙3H2O). It is also found in evaporite minerals such as chlorapatite and sodalite.

Role in biology

Chloride has a major physiological significance, which includes regulation of osmotic pressure, electrolyte balance and acid-base homeostasis. Chloride is present in all body fluids, [8] and is the most abundant extracellular anion which accounts for around one third of extracellular fluid's tonicity. [9] [10]

Chloride is an essential electrolyte, playing a key role in maintaining cell homeostasis and transmitting action potentials in neurons. [11] It can flow through chloride channels (including the GABAA 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 mV at 37 °C in a mammalian cell). [12] Characteristic concentrations of chloride in model organisms are: in both E. coli and budding yeast are 10–200  mM (dependent on medium), in mammalian cells 5–100 mM and in blood plasma 100 mM. [13]

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 (listed by its element name chlorine). Serum chloride levels are mainly regulated by the kidneys through a variety of transporters that are present along the nephron. [14] Most of the chloride, which is filtered by the glomerulus, is reabsorbed by both proximal and distal tubules (majorly by proximal tubule) by both active and passive transport. [15]


The structure of sodium chloride, revealing the tendency of chloride ions (green spheres) to link to several cations. NaCl polyhedra.png
The structure of sodium chloride, revealing the tendency of chloride ions (green spheres) 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 lead to a local breakdown of the protective oxide form in alkaline concrete, so that a subsequent localized corrosion attack takes place. [16]

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 also been shown to change the composition of microbial species at relatively low concentrations. It can also 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. [17]


The chlor-alkali industry is a major consumer of the world's energy budget. This process converts sodium chloride into chlorine and sodium hydroxide, which are used to make many other materials and chemicals. The process involves two parallel reactions:

2 ClCl
+ 2  e
2 H
+ 2 e → H2 + 2 OH
Basic membrane cell used in the electrolysis of brine. At the anode (A), chloride (Cl ) is oxidized to chlorine. The ion-selective membrane (B) allows the counterion Na to freely flow across, but prevents anions such as hydroxide (OH ) and chloride from diffusing across. At the cathode (C), water is reduced to hydroxide and hydrogen gas. Chloralkali membrane.svg
Basic membrane cell used in the electrolysis of brine. At the anode (A), chloride (Cl ) is oxidized to chlorine. The ion-selective membrane (B) allows the counterion Na to freely flow across, but prevents anions such as hydroxide (OH ) 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, it dissociates into Na+ and Cl ions. Salts such as calcium chloride, magnesium chloride, potassium chloride have varied uses ranging from medical treatments to cement formation. [4]

Calcium chloride (CaCl2) is a salt that is marketed in 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. [18]

Examples of covalently-bonded chlorides are phosphorus trichloride, phosphorus pentachloride, and thionyl chloride, all three of which are reactive chlorinating reagents that have been used in a laboratory.

Water quality and processing

A major application involving chloride is desalination, which involves the energy intensive removal of chloride salts to give potable water. In the petroleum industry, the chlorides are a closely monitored constituent of the 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 ]

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. [19]


Chloride salts such as sodium chloride are used to preserve food and as nutrients or condiments.

See also

Related Research Articles

Chlorine Chemical element, symbol Cl and atomic number 17

Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the Pauling scale, behind only oxygen and fluorine. Nitrogen is also more electronegative in many other scales such as Mulliken-Jaffe, Allred-Rochow, Noorizadeh-Shakerzadeh, Nagle, Martynov-Batsanov and Allen electronegativity scales.

Ionic bonding Chemical bonding involving attraction between ions

Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds. It is one of the main types of bonding along with covalent bonding and metallic bonding. Ions are atoms with an electrostatic charge. Atoms that gain electrons make negatively charged ions. Atoms that lose electrons make positively charged ions. This transfer of electrons is known as electrovalence in contrast to covalence. In the simplest case, the cation is a metal atom and the anion is a nonmetal atom, but these ions can be of a more complex nature, e.g. molecular ions like NH+
or SO2−
. In simpler words, an ionic bond results from the transfer of electrons from a metal to a non-metal in order to obtain a full valence shell for both atoms.

In chemistry, a salt is a chemical compound consisting of an ionic assembly of cations and anions. Salts are composed of related numbers of cations and anions so that the product is electrically neutral. These component ions can be inorganic, such as chloride (Cl), or organic, such as acetate ; and can be monatomic, such as fluoride (F), or polyatomic, such as sulfate.

Electrolysis Technique in chemistry and manufacturing

In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. The voltage that is needed for electrolysis to occur is called the decomposition potential. The word "lysis" means to separate or break, so in terms, electrolysis would mean "breakdown via electricity".

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electrically, such a solution is neutral. If an electric potential is applied to such a solution, the cations of the solution are drawn to the electrode that has an abundance of electrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current. This includes most soluble salts, acids, and bases. Some gases, such as hydrogen chloride (HCl), under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological and synthetic polymers, termed "polyelectrolytes", which contain charged functional groups. A substance that dissociates into ions in solution acquires the capacity to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate are examples of electrolytes.

Sodium chloride Chemical compound with formula NaCl

Sodium chloride, commonly known as salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/mol respectively, 100 g of NaCl contains 39.34 g Na and 60.66 g Cl. Sodium chloride is the salt most responsible for the salinity of seawater and of the extracellular fluid of many multicellular organisms. In its edible form of table salt, it is commonly used as a condiment and 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 feedstocks for further chemical syntheses. A second major application of sodium chloride is de-icing of roadways in sub-freezing weather.

The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of ClO
. A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous acid.

Potassium chloride Chemical compound

Potassium chloride is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt-like taste. Potassium chloride can be obtained from ancient dried lake deposits. KCl is used as a fertilizer, in medicine, in scientific applications, and in food processing, where it may be known as E number additive E508.

Calcium chloride Chemical compound

Calcium chloride is an inorganic compound, a salt with the chemical formula CaCl2. It is a white coloured crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide.

Electrolytic cell Cell that uses electrical energy to drive a non-spontaneous redox reaction

An electrolytic cell is an electrochemical cell that uses electrical energy to drive a non-spontaneous redox reaction. It is often used to decompose chemical compounds, in a process called electrolysis—the Greek word lysis means to break up. Important examples of electrolysis are the decomposition of water into hydrogen and oxygen, and bauxite into aluminium and other chemicals. Electroplating is done using an electrolytic cell. Electrolysis is a technique that uses a direct electric current (DC).

Chlorate Anion and term for chemical compounds containing it

The chlorate anion has the formula ClO
. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by a Roman numeral in parentheses, e.g. chlorate (VII), refers to a particular oxyanion of chlorine.

Hypochlorite Ion

In chemistry, hypochlorite is an anion with the chemical formula ClO. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite and calcium hypochlorite. The Cl-O distance in ClO is 210 pm.

The chloralkali process is an industrial process for the electrolysis of sodium chloride solutions. It is the technology used to produce chlorine and sodium hydroxide, which are commodity chemicals required by industry. 35 million tons of chlorine were prepared by this process in 1987. The chlorine and sodium hydroxide produced in this process are widely used in the chemical industry.

Ion exchange Exchange of ions between an electrolyte solution and a solid

Ion exchange is a reversible interchange of one kind of ion present on an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, the purification of chemicals and separation of substances.


A counterion is the ion that accompanies an ionic species in order to maintain electric neutrality. In table salt the sodium ion is the counterion for the chloride ion and vice versa.

Chloroauric acid Chemical compound

Chloroauric acid refers to inorganic compounds with the chemical formula HAuCl
. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl4] anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.

Chlorine gas can be produced by extracting from natural materials, including the electrolysis of a sodium chloride solution (brine) and other ways.

Compounds of lead exist with lead in two main oxidation states: +2 and +4. The former is more common. Inorganic lead(IV) compounds are typically strong oxidants or exist only in highly acidic solutions.

Mixed oxidant solution is a kind of disinfectant which is used for disinfecting, sterilization and eliminating pathogenic microorganisms in water and in many other applications. Using a mixed oxidant solution for water disinfection (see portable water purification), compared to other methods, such as sodium hypochlorite, Calcium hypochlorite, chlorine gas and ozonation may have various benefits such as higher disinfecting power, stable residual chlorine in water, improved taste and odor, elimination of biofilm and safety. Mixed-oxidant solution is produced by electrolysis of sodium chloride brine (sodium chloride) and is a mixture of disinfecting compounds. The main component of this product is chlorine and its derivatives (ClO, HClO and Cl2 solution). It may also contain high amounts of chlorine dioxide (ClO2) solution, dissolved ozone, hydrogen peroxide(H2O2) and oxygen. This is the reason for calling this solution mixed oxidant.

Magnesium chlorate is an inorganic chemical consisting of a magnesium cation and two chlorate anions: its chemical formula is Mg(ClO3)2.


  1. "Chloride ion - PubChem Public Chemical Database". The PubChem Project. USA: National Center for Biotechnology Information.
  2. 1 2 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN   978-0-618-94690-7.
  3. Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, p. 143, ISBN   9781405881180 .
  4. 1 2 Green, John, and Sadru Damji. "Chapter 3." Chemistry. Camberwell, Vic.: IBID, 2001. Print.
  5. Zumdahl, Steven (2013). Chemical Principles (7th ed.). Cengage Learning. p. 109. ISBN   978-1-285-13370-6.
  6. Molleman, Areles (2003). "Patch Clamping: An Introductory Guide to Patch Clamp Electrophysiology". Wiley & Sons. ISBN   978-0-471-48685-5.
  7. Greenwood, N. N. (1984). Chemistry of the elements (1st ed.). Oxford [Oxfordshire]: Pergamon Press. ISBN   9780750628327.
  8. Deane, Norman; Ziff, Morris; Smith, Homer W. (1952). "The distribution of total body chloride in man". Journal of Clinical Investigation. 31 (2). p. 201, Table 1. doi:10.1172/JCI102592. PMC   436401 . PMID   14907900 via PMC.
  9. Berend, Kenrick; van Hulsteijn, Leonard Hendrik; Gans, Rijk O.B. (April 2012). "Chloride: The queen of electrolytes?". European Journal of Internal Medicine. 23 (3): 203–211. doi:10.1016/j.ejim.2011.11.013. PMID   22385875.
  10. Rein, Joshua L.; Coca, Steven G. (1 March 2019). ""I don't get no respect": the role of chloride in acute kidney injury". American Journal of Physiology. Renal Physiology. 316 (3): F587–F605. doi:10.1152/ajprenal.00130.2018. ISSN   1931-857X. PMC   6459301 . PMID   30539650.
  11. Jentsch, Thomas J.; Stein, Valentin; Weinreich, Frank; Zdebik, Anselm A. (2002-04-01). "Molecular Structure and Physiological Function of Chloride Channels". Physiological Reviews. 82 (2): 503–568. doi:10.1152/physrev.00029.2001. ISSN   0031-9333. PMID   11917096.
  12. "Equilibrium potentials".
  13. Milo, Ron; Philips, Rob. "Cell Biology by the Numbers: What are the concentrations of different ions in cells?". Retrieved 24 March 2017.
  14. Nagami, Glenn T. (1 July 2016). "Hyperchloremia – Why and how". Nefrología (English Edition). 36 (4): 347–353. doi: 10.1016/j.nefro.2016.04.001 . ISSN   2013-2514. PMID   27267918.
  15. Shrimanker, Isha; Bhattarai, Sandeep (2020). "Electrolytes". StatPearls. StatPearls Publishing. PMID   31082167.
  16. Criado, M. "13. The corrosion behaviour of reinforced steel embedded in alkali-activated mortar". Handbook of Alkali-Activated Cements, Mortars and Concretes. Woodhead Publishing. pp. 333–372. ISBN   978-1-78242-276-1.
  17. Kaushal, S. S. (19 March 2009). "Chloride". Encyclopedia of Inland Waters. Academic Press. pp. 23–29. ISBN   978-0-12-370626-3.
  18. "Common Salts". Georgia State University.
  19. "Chlorides". Archived from the original on 18 August 2016. Retrieved 14 April 2018.