Properties Of Chlorine And Its Chemistry

Chlorine (Cl2) is a greenish-yellow-colored gas having a specific gravity of 2.48 as compared to air under standard conditions of temperature and pressure. It was discovered in 1774 from the chemical reaction of manganese dioxide (MnN02) and hydrochloric acid (HC1) by the Swedish chemist, Scheele, who believed it to be a compound containing oxygen. In 1810, it was named by Sir Humphrey Davy, who ins isted it was an element (from the Greek work chloros, meaning greenish-yellow). In nature, it is found in the combined state only, usually with sodium as salt (NaCl), carnallite (KMgCl36H20), and sylvite (Kcl).

Chlorine is a member of the halogen (salt-forming) group of elements and is derived from chlorides by the action of oxidizing agents and, most frequently, by electrolysis. As a gas, it combines directly with nearly all elements. At 10° C, 1 volume of water dissolves about 3.10 volumes of chlorine; at 30° C, only 1.77 volumes of Cl2 are dissolved in 1 volume of water.

In addition to being the most widely used disinfectant for water treatment, chlorine is extensively used in a variety of products, including paper products, dyestuffs, textiles, petroleum products, pharmaceuticals, antiseptics, insecticides, foodstuffs, solvents, paints, and other consumer products. Most chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp bleaching, disinfectants, and textile processing. It is also used in the manufacture of chlorates, chloroform, and carbon tetrachloride and in the extraction of bromine. Among other past uses, chlorine served as a war gas during World War I. As a liquid, chlorine is amber colored and is 1.44 times heavier than water. In solid form, it exists as rhombic crystals. Various properties of chlorine are given in Table 2.

Chlorine gas is a highly toxic substance, capable of causing death or permanent injury due to prolonged exposures via inhalation. It is extremely irritating to the mucous membranes of the eyes and the respiratory tract. It will combine with moisture to liberate nascent oxygen to form hydrochloric acid. If both these substances are present in quantity, they can cause inflammation of the tissues with which they come in contact. Pulmonary edema may result if lung tissues are attacked. Chlorine gas has an odor detectable at a concentration as low as 3.55 ppm. Irritation of the throat occurs at 15 ppm. A concentration of 50 ppm is considered dangerous for even short exposures. At or above concentrations of 1,000 ppm, exposure may be fatal. Chlorine can also cause fires or explosions upon contact with various materials. Table 2.5 lists various substances chlorine can react with to create fire hazards. It emits highly toxic fumes when heated and reacts with water or steam to generate toxic and corrosive hydrogen chloride fumes.

Table 2. General properties of chlorine

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