The termchloride refers to a compound or molecule that contains either achlorineanion (Cl−), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by asingle bond (−Cl). The pronunciation of the word "chloride" is/ˈklɔːraɪd/.[3]
A chloride ion (diameter 181 pm) is much larger than a chlorine atom (diameter 99 pm). The chlorine atom's hold on the valence shell is weaker because the chloride anion has one more electron than it does.[5] The ion is colorless and diamagnetic. In aqueous solution, it is highly soluble in most cases; however, for some chloride salts, such assilver chloride,lead(II) chloride, andmercury(I) chloride, they are only slightly soluble in water.[6] In aqueous solution, chloride is bonded by the protic end of the water molecules.
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 includinghypochlorite (ClO−, the active ingredient in chlorinebleach),chlorine dioxide (ClO2),chlorate (ClO− 3), andperchlorate (ClO− 4).
In terms of its acid–base properties, chloride is aweak base as indicated by the negative value of thepKa of hydrochloric acid. Chloride can be protonated bystrong acids, such as sulfuric acid:
NaCl + H2SO4 → NaHSO4 + HCl
Ionic chloride salts react with other salts to exchange anions. The presence of halide ions like chloride can be detected usingsilver nitrate. A solution containing chloride ions will produce a whitesilver chloride precipitate:[7]
Cl− + Ag+ → AgCl
The concentration of chloride in an assay can be determined using achloridometer, which detects silver ions once all chloride in the assay has precipitated via this reaction.
In nature, chloride is found primarily in seawater, which has a chloride ion concentration of 19400 mg/liter.[9] Smaller quantities, though at higher concentrations, occur in certain inland seas and in subterraneanbrine wells, such as theGreat Salt Lake inUtah and theDead Sea in Israel.[10] 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 includehalite (sodium chlorideNaCl),sylvite (potassium chlorideKCl),bischofite (MgCl2∙6H2O),carnallite (KCl∙MgCl2∙6H2O), andkainite (KCl∙MgSO4∙3H2O). It is also found in evaporite minerals such aschlorapatite andsodalite.
Chloride has a major physiological significance,[11] which includes regulation ofosmotic pressure, electrolyte balance and acid-base homeostasis. Chloride is present in allbody fluids,[12] and is the most abundant extracellularanion which accounts for around one third ofextracellular fluid'stonicity.[13][14]
Chloride is usually (though not always) at a higher extracellular concentration, causing it to have a negativereversal potential (around −61 mV at 37 °C in a mammalian cell).[16] Characteristic concentrations of chloride in model organisms are: in bothE. coli and budding yeast are 10–200 mM (dependent on medium), in mammalian cells 5–100 mM and inblood plasma 100 mM.[17]
The concentration of chloride in the blood is calledserum chloride, and this concentration is regulated by thekidneys. A chloride ion is a structural component of some proteins; for example, it is present in theamylase enzyme. For these roles, chloride is one of the essentialdietary minerals (listed by its element namechlorine).Serum chloride levels are mainly regulated by the kidneys through a variety of transporters that are present along thenephron.[19] Most of the chloride, which is filtered by theglomerulus, is reabsorbed by bothproximal anddistal tubules (majorly by proximal tubule) by both active and passive transport.[20]
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 forpitting 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.[21]
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 thedenitrification process, a microbial process essential tonitrate removal and the conservation of water quality, and inhibit thenitrification and respiration of organic matter.[22]
Thechlor-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:
Basic membrane cell used in theelectrolysis 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.
Calcium chloride (CaCl2) is a salt that is marketed inpellet form for removing dampness from rooms and lawn care. Calcium chloride is also used for maintaining unpaved roads and for fortifying roadbases for new construction. In addition, calcium chloride is widely used as ade-icer, since it is effective in lowering themelting point when applied to ice.[23]
A major application involving chloride isdesalination, which involves the energy intensive removal of chloride salts to givepotable water. In thepetroleum industry, the chlorides are a closely monitored constituent of themud 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.[24]
^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.PMID22385875.
