chloride

Chloride refers to the chemical species Cl−, the negatively charged form of chlorine. It is the most common anion in many environments and a key electrolyte in animals, plants, and microbes. Chloride forms salts with a wide range of metals, most notably sodium chloride, also known as table salt.

Natural occurrence and isotopes: chloride is abundant in seawater and in evaporite deposits, where it occurs primarily as halite (NaCl) and related salts. In nature, chlorine has two stable isotopes, Cl-35 and Cl-37, with natural abundances of about 76% and 24%, respectively.

Chemistry and properties: as an aqueous ion, Cl− is highly soluble and typically behaves as a relatively weakly reactive anion. It can be oxidized to chlorine gas by strong oxidizers. Chloride salts are common, and the chloride ion participates in many inorganic and organic reactions. In physiology, chloride contributes to osmotic balance and electrical neutrality.

Biological role: chloride is an essential electrolyte that helps regulate fluid volume, pH, and electrochemical gradients in cells. In humans and other vertebrates, the chloride shift involves exchange of Cl− and bicarbonate across red blood cell membranes and is important for carbon dioxide transport. Stomach acid relies on hydrochloric acid (HCl), formed from chloride and hydrogen ions.

Industrial and environmental applications: industrially, chloride is produced on a large scale by electrolysis of molten sodium chloride, yielding chlorine gas and sodium hydroxide. Chloride salts are used in food as salt, in de-icing, and in water treatment. Environmentally, elevated chloride levels from road salt and industrial discharges can impact freshwater ecosystems and corrode infrastructure, prompting regulatory guidelines for drinking water and discharges.