hydroxide

/huy drok"suyd, -sid/, n.

a chemical compound containing the hydroxyl group.

[1820-30; HYDR-² + OXIDE]

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Any compound with one or more functional groups made up of one atom each of hydrogen and oxygen, bonded together and acting as the hydroxide anion (OH^-).

Hydroxides include the familiar alkalies of laboratory and industrial processes. Those of the alkali metals (lithium, sodium, potassium, rubidium, and cesium), the strongest bases, are the most stable and soluble; those of the alkaline earth metals (calcium, barium, and strontium), also soluble strong bases, are less stable. The hydroxides of most other metals are only slightly soluble but neutralize acids; some are "amphoteric," reacting with both acids and bases. In compounds in which OH is un-ionized and covalently bonded (e.g., in methanol, CH₃OH), it is known as a hydroxyl group.

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▪ chemical compound

      any chemical compound containing one or more groups, each comprising one atom each of oxygen and hydrogen bonded together and functioning as the negatively charged ion OH^-. The positively charged portion of the compound usually is the ion of a metal (e.g., sodium, magnesium, or aluminum), although it may be an organic group (e.g., guanidinium or tetramethylammonium). It is preferable to characterize the presence of the un-ionized, covalently bonded hydroxyl group OH by the prefix hydroxy, as in the organic compound hydroxyacetic acid, CH₂OHCOOH, or by the suffix ol, as in methanol, CH₃OH, and in coordination compounds by the prefix hydroxo, as in potassium tetrahydroxoaurate, KAu(OH)₄.

      The hydroxides include the familiar alkalies of the laboratory and industrial processes. The hydroxides of the alkali metals, lithium, sodium, potassium, rubidium, and cesium, are the strongest bases and the most stable and most soluble of the hydroxides. Sodium hydroxide, NaOH, also known as caustic soda or lye, is of great industrial importance. Calcium, barium, and strontium—all alkaline earth metals—form soluble hydroxides that are strong bases but are less stable than the alkali hydroxides. Of these, calcium hydroxide, Ca(OH)₂, commonly known as slaked lime, is the most common. With the exception of thallium hydroxide (TlOH), the hydroxides of other metals, such as magnesium, iron, bismuth, nickel, cobalt, and copper, are only sparingly soluble in water but neutralize acids. The hydroxides of beryllium, lead, zinc, aluminum, chromium (trivalent), tin (divalent), gold (trivalent), and certain other metals show both acidic and basic properties; i.e., they dissolve in water solutions of either bases or acids. Hydroxides and other substances, such as oxides and sulfides, with these dual properties are called amphoteric.

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