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chlorate(klōr`āt, klôr`–) and
perchlorate(pərklōr`āt, –klôr`–), saltssalt,
chemical compound (other than water) formed by a chemical reaction between an acid and a base (see acids and bases). Characteristics and Classification of Salts
The most familiar salt is sodium chloride, the principal component of common table salt.
..... Click the link for more information. of chloric acid, HClO3, and perchloric acid, HClO4, respectively.
Chloric Acid and Its Salts
Chloric acid, HClO3·7H2O, is a colorless substance that occurs only in solution. It is a strong acid and a strong oxidizing agent that decomposes if heated above 40°C;. Under certain conditions it forms oxygen, water, and the explosive gas chlorine dioxide, ClO2; under other conditions it forms perchloric acid and hydrochloric acid.
Formation of Chlorates
A chlorate may be formed (together with the corresponding chloride) by heating the hypochlorite; e.g., 3Ca(ClO)2→Ca(ClO3)2+2CaCl2. This reaction takes place when chlorine gas is passed into a hot aqueous solution of a metal hydroxide; the hypochlorite is formed and decomposes almost immediately. Commercially, a chlorate is derived when a hot aqueous metal chloride solution is decomposed by electrolysis, forming chlorine gas at the anode and metal hydroxide at the cathode (with evolution of hydrogen); the chlorine reacts with the hydroxide to form the hypochlorite, which decomposes to form the chlorate.
Commercial Uses of Chlorates
The most industrially important chlorate is potassium chlorate, or chlorate of potash, KClO3; sodium chlorate, or chlorate of soda, NaClO3, is also used. Potassium chlorate is a colorless crystalline substance that melts at 356°C; and decomposes violently at about 400°C;. It is a powerful oxidizing agent and is used in making explosives and matches; a mixture of potassium chlorate with phosphorus, sulfur, or any of numerous organic compounds (e.g., charcoal or sugar) explodes upon friction or percussion. When a chlorate is heated, oxygen is evolved, often explosively, and the chloride is formed; e.g., 2KClO3→2KCl+3O2. The reaction proceeds controllably at lower temperatures if a catalyst, e.g., manganese dioxide, is used; this provides a convenient source of oxygen. If the chlorate is heated carefully at a lower temperature so that no oxygen is given off, the perchlorate and chloride are formed; e.g., 4KClO3→3KClO4+KCl.
Perchloric Acid and Its Salts
Perchloric acid, HClO4, is a volatile, unstable, colorless liquid that is a strong, corrosive acid and a powerful oxidizing agent, especially when hot. It explodes if heated to about 90°C; or on contact with combustible materials. The monohydrate, HClO4·H2O, is fairly stable and forms needlelike crystals that melt at 50°C;. It explodes if heated to 110°C;. The dihydrate, HClO4·2H2O, is a stable liquid that boils at 200°C;.
Formation of Perchlorates
Perchloric anhydride, or chlorine heptoxide, Cl2O7, is a colorless, oily liquid that boils at 82°C; without exploding but that may be detonated by shock; it can be prepared by adding phosphorus pentoxide to cold perchloric acid. The perchlorate free radical (chlorine tetroxide, ClO4) can be prepared by adding bromine to silver perchlorate; it is extremely reactive and unstable.
Commercial Uses of Perchlorates
Perchlorates are safer to handle than chlorates; they are more stable when exposed to heat or shock. Potassium perchlorate, KClO4, is perhaps most widely used, e.g., in matches, fireworks, and explosives. It is a colorless crystalline substance that melts at about 610°C;.
any one of a group of salts of chloric acid, HClO3. Chlorates are crystalline compounds that are stable at ordinary temperatures but decompose upon heating or in the presence of catalysts with the liberation of oxygen. Most are readily soluble in water and some organic solvents. Chlorates form explosive mixtures with organic and readily oxidizable compounds. Sodium chlorate, potassium chlorate, calcium chlorate, and magnesium chlorate are produced on an industrial scale.
Potassium chlorate, KClO3, has a density of 2.344 g/cm3 and a melting point of 370°C. It was first produced in 1786 by C. L. Berthollet by the addition of chlorine to a concentrated solution of potassium hydroxide. Its solubility in water is 32.4 g/liter (g/l) at 0°C, 170.5 g/l at 50°C, and 437 g/l at 100°C. Potassium chlorate is nonhygroscopic. It decomposes at about 400°C with the liberation of oxygen; however, in the presence of catalysts, such as MnO2 and Fe2O3, it decomposes at about 150°–200°C. Chemically pure potassium chlorate explodes at 550°–600°C, and in a mixture with sulfur, phosphorus, and many organic compounds, it explodes upon impact or friction. Its explosiveness increases in the presence of bromates and ammonium salts. Potassium chlorate is produced by the exchange decomposition of calcium chlorate or sodium chlorate with KCl. It is used in the production of matches and pyrotechnical substances.
Sodium chlorate, NaClO3, has a density of 2.49 g/cm3 at 15°C and a melting point of 248°C. Its solubility in water is 612 g/l at 0°C, 870 g/l at 50°C, and 1,190 at g/l at 100°C. Slightly hygroscopic, it is similar to potassium chlorate in chemical properties. It is produced by the electrolysis of aqueous solutions of NaCl in cells without diaphragms. It is used to obtain chlorine dioxide and in the production of other chlorates and perchlorates.
Calcium chlorate, Ca(ClO3)2, is a very hygroscopic salt. With water it forms the crystal hydrates Ca(ClO3) · nH2O, where n ranges from 1 to 6. It disperses in the air. Calcium chlorate is produced by the chlorination of milk of lime:
6Ca(OH)2 + 6Cl2 = Ca(ClO3)2 + 5CaCl2 + 6H2O
It is used as an intermediate in the production of potassium chlorate; it is also used in agriculture as a herbicide and defoliant.
Magnesium chlorate, Mg(ClO3)2, is a very hygroscopic salt. With water it forms crystal hydrates, such as Mg(ClO3)2 · 6H2O. Anhydrous magnesium chlorate has not been obtained. Magnesium chlorate disperses in the air. The crystal hydrate is obtained by melting sodium chlorate with bischofite:
2NaClO3 + MgCl2 · 6H2O = Mg(ClO3)2 · 6H2O + 2NaCl
It is flammable and explosive. Magnesium chlorate is used for the preharvest removal of leaves from the cotton plant and for the desiccation of sunflower, rice, seed plants of leguminous crops, and sugar-beet transplantations.
Chlorates have low toxicity. Chronic chlorate poisoning results from internal consumption or the breathing of chlorate dust.
L. M. IAKIMENKO