The chloride
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conv ...
is the
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
(negatively charged ion) Cl
−. It is formed when the
element chlorine
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
halogen) gains an
electron or when a
compound
Compound may refer to:
Architecture and built environments
* Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall
** Compound (fortification), a version of the above fortified with defensive struc ...
such as
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride g ...
is dissolved in water or other polar solvents. Chloride salts such as
sodium chloride are often very soluble in water.
[Green, John, and Sadru Damji. "Chapter 3." ''Chemistry''. Camberwell, Vic.: IBID, 2001. Print.] It is an essential
electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting
nerve impulses
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ca ...
and regulating liquid flow in and out of cells. Less frequently, the word ''chloride'' may also form part of the "common" name of
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one elemen ...
s in which one or more chlorine
atoms are
covalently bonded
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
. For example, methyl chloride, with the standard name
chloromethane
Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, odorless, flammable gas. Methyl chloride is a crucial reagent in industrial ...
(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). This is because the chloride anion has 1 more electron than the chlorine atom, reducing the hold of the nucleus on the valence shell. 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
Silver chloride is a chemical compound with the chemical formula Ag Cl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heat ...
,
lead(II) chloride
Lead(II) chloride (PbCl2) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the m ...
, and
mercury(I) chloride
Mercury(I) chloride is the chemical compound with the formula Hg2Cl2. Also known as the mineral calomel (a rare mineral) or mercurous chloride, this dense white or yellowish-white, odorless solid is the principal example of a mercury(I) compound. ...
, they are only slightly soluble in water. 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
Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...
),
chlorine dioxide
Chlorine dioxide is a chemical compound with the formula ClO2 that exists as yellowish-green gas above 11 °C, a reddish-brown liquid between 11 °C and −59 °C, and as bright orange crystals below −59 °C. It is usually ...
(ClO
2),
chlorate
The chlorate anion has the formula ClO3-. 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 ...
(), and
perchlorate ().
In terms of its acid–base properties, chloride is a
weak base
A weak base is a base that, upon dissolution in water, does not dissociate completely, so that the resulting aqueous solution contains only a small proportion of hydroxide ions and the concerned basic radical, and a large proportion of undissociat ...
as indicated by the negative value of the
p''K''a of hydrochloric acid. Chloride can be protonated by
strong acid
Acid strength is the tendency of an acid, symbolised by the chemical formula HA, to dissociate into a proton, H+, and an anion, A-. The dissociation of a strong acid in solution is effectively complete, except in its most concentrated solutions. ...
s, such as sulfuric acid:
:NaCl + H
2SO
4 → NaHSO
4 + HCl
Ionic chloride salts reaction 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
Silver chloride is a chemical compound with the chemical formula Ag Cl. This white crystalline solid is well known for its low solubility in water (this behavior being reminiscent of the chlorides of Tl+ and Pb2+). Upon illumination or heat ...
precipitate:
: Cl
− + Ag
+ → AgCl
The concentration of chloride in an assay can be determined using a
chloridometer A chloridometer is a measuring instrument used to determine the concentration of chloride ions (Cl–) in a solution. It uses a process known as coulometric titration or ''amperostatic coulometry'', the accepted electrochemistry reference method t ...
, which detects silver ions once all chloride in the assay has precipitated via this reaction.
Chlorided silver electrodes are commonly used in
electrophysiology
Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , ''-logia'') is the branch of physiology that studies the electrical properties of bi ...
.
Other oxyanions
Chlorine can assume
oxidation states of −1, +1, +3, +5, or +7. Several neutral
chlorine oxide
Chlorine and oxygen can bond in many ways:
* chlorine monoxide, , chlorine (II) oxide
* chlorine peroxide, , dimer of chlorine (II) oxide
* chlorine dioxide, , chlorine (IV) oxide
* chloroperoxyl,
* chlorine trioxide, ClO3, chlorine (VI) oxid ...
s are also known.
:
Occurrence in nature
In nature, chloride is found primarily in seawater, which has a chloride ion concentration of 19400 mg/liter. Smaller quantities, though at higher concentrations, occur in certain inland seas and in subterranean
brine well
A salt well (or brine well) is used to mine salt from caverns or deposits. Water is used as a solution to dissolve the salt or halite deposits so that they can be extracted by pipe to an evaporation process, which results in a brine or dry produc ...
s, such as the
Great Salt Lake in
Utah and the
Dead Sea
The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Bank t ...
in
Israel.
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
Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), 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/ ...
),
sylvite
Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades o ...
(potassium chloride
KCl
Potassium chloride (KCl, or potassium salt) 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 ...
),
bischofite (MgCl
2∙6H
2O),
carnallite
Carnallite (also carnalite) is an evaporite mineral, a hydrated potassium magnesium chloride with formula KMgCl3·6(H2O). It is variably colored yellow to white, reddish, and sometimes colorless or blue. It is usually massive to fibrous with rar ...
(KCl∙MgCl
2∙6H
2O), and
kainite
Kainite ( or ) (KMg(SO4)Cl·3H2O) is an evaporite mineral in the class of "Sulfates (selenates, etc.) with additional anions, with H2O" according to the Nickel–Strunz classification. It is a hydrated potassium-magnesium sulfate-chloride, natura ...
(KCl∙MgSO
4∙3H
2O). It is also found in evaporite minerals such as
chlorapatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common ...
and
sodalite.
Role in biology
Chloride has a major physiological significance, which includes regulation of
osmotic pressure
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane.
It is also defined as the measure of the tendency of a solution to take in a pure ...
, electrolyte balance and acid-base homeostasis. Chloride is present in all
body fluid
Body fluids, bodily fluids, or biofluids, sometimes body liquids, are liquids within the human body. In lean healthy adult men, the total body water is about 60% (60–67%) of the total body weight; it is usually slightly lower in women (52-55%). ...
s, and is the most abundant extracellular
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
which accounts for around one third of
extracellular fluid's
tonicity.
Chloride is an essential
electrolyte, playing a key role in maintaining cell
homeostasis
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and i ...
and transmitting
action potentials
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ca ...
in neurons. It can flow through
chloride channels
Chloride channels are a superfamily of poorly understood ion channels specific for chloride. These channels may conduct many different ions, but are named for chloride because its concentration ''in vivo'' is much higher than other anions. Several ...
(including the
GABAA receptor) and is transported by
KCC2 and
NKCC2
The Na-K-Cl cotransporter (NKCC) is a protein that aids in the secondary active transport of sodium, potassium, and chloride into cells. In humans there are two isoforms of this membrane transport protein, NKCC1 and NKCC2, encoded by two differ ...
transporters.
Chloride is usually (though not always) at a higher extracellular concentration, causing it to have a negative
reversal potential In a biological membrane, the reversal potential is the membrane potential at which the direction of ionic current reverses. At the reversal potential, there is no net flow of ions from one side of the membrane to the other. For channels that are pe ...
(around −61 mV at 37 °C in a mammalian cell). 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
Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intr ...
100 mM.
The concentration of chloride in the blood is called
serum chloride, and this concentration is regulated by the
kidneys
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ...
. A chloride ion is a structural component of some proteins; for example, it is present in the
amylase
An amylase () is an enzyme that catalyses the hydrolysis of starch (Latin ') into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of ...
enzyme. For these roles, chloride is one of the essential
dietary mineral (listed by its element name ''chlorine'').
Serum
Serum may refer to:
* Serum (blood), plasma from which the clotting proteins have been removed
**Antiserum, blood serum with specific antibodies for passive immunity
* Serous fluid, any clear bodily fluid
*Truth serum, a drug that is likely to mak ...
chloride levels are mainly regulated by the kidneys through a variety of transporters that are present along the
nephron
The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure c ...
. 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.
Corrosion
The presence of chlorides, such as in seawater, significantly worsens the conditions for
pitting corrosion
Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic (oxidation re ...
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.
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.
Production
The
chlor-alkali
The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are commodi ...
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 Cl
− → + 2
e−
:2 + 2 e
− → H
2 + 2 OH
−
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
Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide.
Ca ...
,
magnesium chloride,
potassium chloride
Potassium chloride (KCl, or potassium salt) 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 sa ...
have varied uses ranging from medical treatments to cement formation.
Calcium chloride (CaCl
2) 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.
Examples of
covalently-bonded chlorides are
phosphorus trichloride
Phosphorus trichloride is an inorganic compound with the chemical formula PCl3. A colorless liquid when pure, it is an important industrial chemical, being used for the manufacture of phosphites and other organophosphorus compounds. It is toxic ...
,
phosphorus pentachloride
Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and mois ...
, 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
Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance, as in soil desalination, which is an issue for agriculture. Saltw ...
, 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.
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.
Food
Chloride salts such as
sodium chloride are used to
preserve food and as nutrients or
condiment
A condiment is a preparation that is added to food, typically after cooking, to impart a specific flavor, to enhance the flavor, or to complement the dish. A table condiment or table sauce is more specifically a condiment that is served separat ...
s.
See also
*
Halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...
(compounds of halogens)
*
Renal chloride reabsorption
References
{{Chlorides
Anions
Leaving groups
Dietary minerals