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alkali(ăl`kəlī) [Arab., al-gili=ashes of saltwort], hydroxidehydroxide
, chemical compound that contains the hydroxyl (−OH) radical. The term refers especially to inorganic compounds. Organic compounds that have the hydroxyl radical as a functional group are called alcohols; the hydroxyl radical is also present in the carboxyl group
..... Click the link for more information. of an alkali metalalkali metals,
metals found in Group 1 of the periodic table. Compared to other metals they are soft and have low melting points and densities. Alkali metals are powerful reducing agents and form univalent compounds.
..... Click the link for more information. . Alkalies are readily soluble in water and form strongly basic solutions with a characteristic acrid taste. They neutralize acids, forming salts and water. Strong alkalies (e.g., those of sodium or potassium) are sometimes called caustic alkalies. The term alkali originally applied to salts obtained from plant ashes and is sometimes applied to a carbonate of sodium or potassium or to the hydroxide of an alkaline-earth metalalkaline-earth metals,
metals constituting Group 2 of the periodic table. Generally, they are softer than most other metals, react readily with water (especially when heated), and are powerful reducing agents, but they are exceeded in each of these properties by the
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a base in aqueous solution. Aqueous alkaline solutions have high concentrations of OH– (hydroxyl) ions. Alkalies include the hydroxides of the alkali metals, the alkaline-earth metals, and ammonium.
Most alkalies are highly hygroscopic white solid compounds. Their dissolution in water is accompanied by the liberation of large amounts of heat. Alkaline solutions change the color of acid-base indicators. The strongest, that is, caustic, alkalies are the hydroxides of the alkali metals, such as NaOH and KOH, while the weakest alkalies are ammonium hydroxide and the hydroxides of the alkaline-earth metals, such as Ca(OH)2 and Ba(OH)2. Also sometimes considered as alkalies are the salts of strong bases and weak acids (seeACIDS AND BASES), whose aqueous solutions exhibit alkaline reactions, for example, the hydro-sulfides NaSH and KSH, the carbonates Na2CO3 and K2CO3, the hydrocarbonate NaHCO3 and the borax Na2B4O7. Alkalies are commonly used in laboratory work and in industry (seeSODIUM HYDROXIDE; POTASSIUM HYDROXIDE; and CALCIUM HYDROXIDE).