sodium hydrogen carbonate: see sodium bicarbonate.

sodium carbonate, chemical compound, Na₂CO₃, soluble in water and very slightly soluble in alcohol. Pure sodium carbonate is a white, odorless powder that absorbs moisture from the air, has an alkaline taste, and forms a strongly alkaline water solution. It is one of the most basic industrial chemicals. Sodium carbonate decahydrate, Na₂CO₃·10H₂O, is a colorless, transparent crystalline compound commonly called sal soda or washing soda. Because seaweed ashes were an early source of sodium carbonate, it is often called soda ash or, simply, soda. The Solvay process provides most sodium carbonate for industrial use. It is found in large natural deposits and is mined in Wyoming; it is also recovered (with other chemicals) from lake brines in California. The principal uses of sodium carbonate are in the manufacture of glass and the production of chemicals. It is also used in processing wood pulp to make paper, in making soaps and detergents, in refining aluminum, in water softening, and in many other applications. The Leblanc process, the first successful commercial process for making soda, is no longer used in the United States but played a major role in the Industrial Revolution.

potassium carbonate, chemical compound, K₂CO₃, white, crystalline, deliquescent substance that forms a strongly alkaline water solution. It is available commercially as a white, granular powder commonly called potash, or pearl ash. It was originally obtained from wood ashes or from the residue left in pots after certain plants, e.g., kelp, were burned in them. It is prepared commercially chiefly by electrolysis of potassium chloride to form potassium hydroxide, which is then carbonated (e.g., by adding carbon dioxide gas). It is used in the manufacture of soft soaps and glass, for washing wool, and in the production of other potassium compounds.

carbonate, chemical compound containing the carbonate radical or ion, CO₃^-2. Most familiar carbonates are salts that are formed by reacting an inorganic base (e.g., a metal hydroxide) with carbonic acid. Normal carbonates are formed when equivalent amounts of acid and base react; bicarbonates, also called acid carbonates or hydrogen carbonates, are formed when the acid is present in excess. Sodium carbonate, Na₂CO₃, sodium bicarbonate, NaHCO₃, and potassium carbonate, K₂CO₃, are widely used. Smelling salts is ammonium carbonate. Calcium carbonate is found in shells of animals and in Iceland spar, limestone, and marble; it is used in the production of lime (calcium oxide). Barium carbonate occurs as the mineral witherite. Magnesium carbonate occurs as magnesite and in dolomite (with calcium carbonate). Iron carbonate is a ferrous compound that occurs in nature as siderite. White lead used as a pigment in paints is basic lead carbonate. Only ammonium, potassium, and sodium carbonates are readily soluble in water. Alkali metal carbonates are stable when heated, but other carbonates decompose, releasing carbon dioxide. Carbonates also give off carbon dioxide when treated with dilute acids, e.g., hydrochloric acid.

calcium carbonate, CaCO₃, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. Calcium carbonate is largely insoluble in water but is quite soluble in water containing dissolved carbon dioxide, combining with it to form the bicarbonate Ca(HCO₃)₂. Such reactions on limestone (which is mainly composed of calcite) account for the formation of stalactites and stalagmites in caves. Iceland spar is a pure form of calcium carbonate and exhibits birefringence, or double refraction.

Any member of a family of minerals that contains the carbonate ion, CO₃²⁻, as the basic structural unit. The carbonates are among the most widely distributed minerals in the earth's crust; the most common are calcite, dolomite, and aragonite. Dolomite replaces calcite in limestones; when this replacement is extensive, the rock is called dolomite. Other relatively common carbonate minerals are siderite, rhodochrosite, strontianite (strontium-rich); smithsonite (zinc-rich); witherite (barium-rich); and cerussite (lead-rich).

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Any member of two classes of chemical compounds—one inorganic and the other organic—that are derived from carbon dioxide (CO₂) or its water solution, carbonic acid (H₂CO₃). Inorganic carbonates (MCO₃ or M₂CO₃, where M is a metal atom of, e.g., calcium or sodium) are salts of carbonic acid. The shells and other hard parts of shellfish are calcium carbonate, as is the limestone they turn into. Many other minerals, including calcite, dolomite, and aragonite, consist of or contain carbonates. Sodium carbonate is one of the world's most important basic chemical commodities. Organic carbonates are esters of carbonic acid and various alcohol groups (methyl, ethyl, or phenyl). These are liquids used as solvents and to synthesize plastics and other compounds.

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