The chloride ion is the anionCl−. It is formed when the elementchlorine 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. It is an essential electrolyte located in all body fluids responsible for maintaining acid/base balance, transmitting nerve impulses and regulating fluid in and out of cells. Less frequently, the wordchloride 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 is an organic compound with a covalent C−Cl bond in which the chlorine is not an anion.
Electronic properties
A chloride ion is much larger than a chlorine atom, 167 and 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 chloride, and mercury chloride, they are 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, chlorine dioxide, chlorate, and perchlorate. 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: 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 ion: 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 vivoelectrophysiology.
Other oxyanions
Chlorine can assume oxidation states of −1, +1, +3, +5, or +7. Several neutral chlorine oxides are also known.
Sea water contains 1.94% chloride. Some chloride-containing minerals include the chlorides of sodium, potassium, and magnesium, hydrated MgCl2.
Role in biology
Chloride is found as an electrolyte, can flow through chloride channels and is transported by KCC2 and NKCC2 transporters. Chloride is usually at a higher extracellular concentration, causing it to have a negative reversal potential. Chloride is an essential electrolyte, playing a key role in maintaining cell homeostasis and transmitting action potentials in neurons. Characteristic concentrations of chloride in model organisms are: in both E. coli and budding yeast are 10-200mM, in mammalian cell 5-100mM and in blood plasma 100mM. 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, e.g., it is present in the amylase enzyme. For these roles, chloride is one of the essential dietary mineral.
Corrosion
The presence of chlorides, e.g. in seawater, significantly worsens the conditions for pitting corrosion of most metals by enhancing the formation, which, like most chloride salts, is colorless and water-soluble.
Production
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: of brine. At the anode, chloride is oxidized to chlorine. The ion-selective membrane allows the counterion Na+ to freely flow across, but prevents anions such as hydroxide and chloride from diffusing across. At the cathode, 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. Calcium chloride 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 pentachloride, and thionyl chloride, all three of which are reactive chlorinating reagents that have been used in a laboratory.
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 / groundwater fecal contamination, as chloride is a non-reactive solute and ubiquitous to sewage & 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 condiments.
