Chlorine

Chlorine is used to purify drinking water and in compounds it is used to produce paper products, dyes, textiles, petroleum products, medicines, antiseptics, insecticides, foods, solvents, paints, plastics and many other products.   Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, wood pulp bleaching, disinfectants and textile production.   Other uses are as chlorates, which are strong oxidizers, chloroform, and in extracting bromine.   In organic compounds, chlorine is substituted for hydrogen to produce other useful compounds. ^{Lide 4-8}   Chlorine is combined with hydrogen to produce the industrially important hydrochloric acid, HCl.

Chlorine is essential to life.  Chlorine ions, Cl^-, are found throughout the human body; that is, in the blood, in the cells and in the intercellular fluids where it acts act an electrolyte for nerve impulse propagation.   It activates an enzyme in saliva and helps maintain the body pH level (acid-base balance).   Hydrochloric acid, HCl, in the stomach digests food.   Source: table salt (NaCl) and processed foods.   However, excessive salt intake of results in high-blood pressure (hypertension), which causes the thickening of heart walls and dilation of the heart cavity.  This can result in atherosclerosis.   Chlorine is highly toxic and was used as a lethal gas during World War I.

In plants, chlorine is involved in osmosis, which is the movement of water or solutes in cells, the ionic balance necessary for plants to take up mineral elements and in photosynthesis.   Deficiency symptoms include wilting, stubby roots, chlorosis (yellowing) and bronzing.   The chlorine ion, Cl^¯, is an electrolyte used by plants to maintain ionic balance.   It can be lost by leaching.   Some plants may show signs of toxicity if chlorine levels are too high. ^{Morgan n.p.}

Chlorine was unknowingly discovered in 1774 by Carl Scheele, a Swedish chemist, who thought it was a compound of oxygen, and no element.   Sir Humphrey Davy, a British chemist, showed in 1810 that hydrochloric acid contained no oxygen, but rather chlorine.   He isolated it and claimed it as his discovery.  Chlorine is too reactive to be found free.   It occurs as common table salt, sodium chloride, NaCl.   It also occurs as carnallite, KMgCl₃•6H₂O, and sylvite, KCl (potassium chloride).

Chlorine is manufactured industrially as a byproduct in the manufacture of caustic soda, NaOH, and by the electrolysis of brine, a solution of salt, NaCl, in water: