The chloride
ion is the
anion (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 i ...
(a
halogen) gains an
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
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 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 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
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,
lead(II) chloride, 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),
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 (), 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
Silver nitrate is an inorganic compound with chemical formula . It is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides. It was once called ''lunar causti ...
. A solution containing chloride ions will produce a white
silver chloride 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.
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) oxide
* ...
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 wells, such as the
Great Salt Lake in
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
and the
Dead Sea in
Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
.
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 (potassium chloride
KCl),
bischofite (MgCl
2∙6H
2O),
carnallite (KCl∙MgCl
2∙6H
2O), and
kainite (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 en ...
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, and is the most abundant extracellular
anion which accounts for around one third of
extracellular fluid
In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a low ...
's
tonicity
In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane-im ...
.
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 ...
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 ...
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 differe ...
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 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; bloo ...
. 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 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 ...
. Most of the chloride, which is filtered by the
glomerulus
''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn".
''Glomerulus'' may refer to:
* the filter ...
, 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 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 commodit ...
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
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
NaCl. In
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
, 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
Magnesium chloride is the family of inorganic compounds with the formula , where x can range from 0 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in natu ...
,
potassium chloride 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
Deicing is the process of removing snow, ice or frost from a surface. Anti-icing is the application of chemicals that not only deice but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prev ...
, since it is effective in lowering the
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
when applied to ice.
Examples of
covalently-bonded chlorides are
phosphorus trichloride,
phosphorus pentachloride, and
thionyl chloride
Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...
, 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.
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 (compounds of halogens)
*
Renal chloride reabsorption
References
{{Chlorides
Anions
Leaving groups
Dietary minerals