A chloride ion is formed when chlorine, a very reactive nonmetallic element, picks up one electron to form an anion (negatively charged ion) Cl-. Most common chlorides are water soluble, the main exceptions being AgCl, Hg2Cl2, and Cu2Cl2. A few, such PbCl2, are slightly soluble. The oxygenated chlorine compounds are mostly water soluible. 5. When a metallic element combines with a chloride ion a salt is formed.

Chlorides are widely present in nature, including mineral sediments, natural water, air above oceans and seas, human and animal excretions, and wastewater. An average human body excretes 5 to 9 grams of chlorides per day. Chlorides are among the most stable constituents of natural water, and as such, they take part in very few chemical reactions. Because chlorides tend to be stable and present in human excretions, and elevated concentration of chlorides in natural water is often used as an indicator of fecal contamination. 4

Common Chlorides

Sodium chloride, NaCl, or common salt, is the form in which the sodium metal is found in nature. It plays an important biological role in maintaining the osmotic tension of blood and tissues.

Hydrogen chloride gas (HCl) is a combustion product derived from the burning of coal and municipal incinerators. It is highly soluble in water and forms hydrochloric acid, which is extremly corrosive.

Calcium chloride, CaCl2, is an ionic compound of calcium and chlorine. It is highly soluble in water and it is deliquescent. It is a salt that is solid at room temperature. Calcium chloride has several common applications such as brine for refrigeration plants, ice and dust control on roads, and in cement. It can be produced directly from limestone, but large amounts are also produced as a by-product of the Solvay process. Because of its hygrpscopic nature, it must be kept in tightly-sealed containers. 3 This salt is used to replenish calcium levels, as an acid-producing diuretic, and as an antidote for magnesium poisoning.

Injection of calcium chloride solution containing 1% lignocaine hydrochloride for sterilization of mature male cats.
Injection of calcium chloride solution containing 1% lignocaine hydrochloride for sterilization of mature male cats.
Source: PubMed

Magnesium chloride, MgCl2, is used in medicine as a source of magnesium ions, which are essential for many cellular activities. It has also been used as a cathartic and in alloys.

Mercury chloride, HgCl2, is highly toxic compound that volatizes slightly at ordinary temperature and substantially at 100 degrees C. It is harmful to mucous membranes and used as a topical antiseptic and disinfectant.

Potassium chloride, KCl, is commonly known as "Muriate of Potash." It varies in color from pink, red, to white depending on the mining adn recovery process used. White potash is used primarily for making liquid starter fertilizers. It is also used in pharmaceutical and food industries. 3

Ferric chloride, FeCl3, or iron(III) chloride, is an industrial scale commodity chemical compound with many applications. The color of ferric chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red. Ferric chloride is deliquescent, fuming in moist air. When dissolved in water, it undergoes hydrolysis and gives off heat. The resulting brown acidic solution is used as a coagulant in sewage treatment In the production of drinking water, ferric chloride reacts with hydroxide ion in slightly basic water to form a floc of iron(III) hydroxide formulated as FeO(OH)-, that remove suspended materials. 3

Ammonium chloride (NH4Cl), sometimes called "sal ammoniac," is a white water-soluble crystalline salt. The aqueous ammonium chloride solution is slightly acidic. When ingested it produces acidifying, expectorant and diuretic effects.3 It is used in galvanizing iron, textile dyeing, and in manufacturing dry cell battries.

Sodium hypochlorite (ClNaO) solution (Dakin's Solution) is an effective germicide, viricide, and deodorant because of the oxydixing power of hypochlorous acid.

Calcium hypochlorite, Ca(OCl)2, or common bleaching powder, is one of the most effective and least expensive disinfectants. 2

Physiological Importance Of Chlorides

Chloride (Cl-), a blood electyrolyte, is a major anion that exists mainly in the extracellular spaces as part of NaCl or HCl. Chloride maintains cellular integrity through its influence on osmotic pressure and acid-base and water balance. It has the reciprocal power of increasing or decreasing in concentration in response in concentrations of other anions. In metabolic acidosis, there is a reciprocal rise in chloride concentration when the bicarbonate concentration drops. Similarly, when aldosterone directly causes an increase in the absorption of Na, the indirect effect is the increase in the absorption of chloride. 2

At a chloride concentration of 250 mg/l or higher, water has a distinctly salty taste which most people cannot tolerate The ingestion of reasonable amounts of chlorides is not harmful to most people. However, if it is only sodium chloride (NaCl), it can have an adverse effect on those who need to adhere to salt intake restrictions. Chlorides tend to be harmful to many types of vegetation. 4

Chlorides are excreted with cations during massive diuresis and are lost from the GI tract when vomiting, diarrhea, or intestinal fistulas occur. 2 A sterile solution of three chlorides, NaCl, KCl, and CaCl2, is used as balanced electrolyte solution for electrolyte replenishment.


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  2. Frances Talaska Fischbach, Marshall Barnett Dunning. A manual of laboratory and diagnostic tests
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  4. Milan Dimkic, Heinz-J├╝rgen Brauch, Michael C. Kavanaugh Groundwater management in large river basins
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