alkali
In chemistry, a base that is soluble in water. Alkalis neutralize acids, and solutions of alkalis are soapy to the touch. The strength of an alkali is measured by its hydrogen-ion concentration, indicated by the pH value. They may be divided into strong and weak alkalis: a strong alkali (for example, potassium hydroxide, KOH) ionizes completely when dissolved in water, whereas a weak alkali (for example, ammonium hydroxide, NH4OH) exists in a partially ionized state in solution. All alkalis have a pH above 7.0.
The hydroxides of metals are alkalis. Those of sodium and potassium are corrosive; both were historically derived from the ashes of plants.
The four main alkalis are sodium hydroxide (caustic soda, NaOH); potassium hydroxide (caustic potash, KOH); calcium hydroxide (slaked lime or limewater, Ca(OH)2); and aqueous ammonia (NH3(aq)). Their solutions all contain the hydroxide ion OH-, which gives them a characteristic set of properties.
The hydroxides of metals are alkalis. Those of sodium and potassium are corrosive; both were historically derived from the ashes of plants.
The four main alkalis are sodium hydroxide (caustic soda, NaOH); potassium hydroxide (caustic potash, KOH); calcium hydroxide (slaked lime or limewater, Ca(OH)2); and aqueous ammonia (NH3(aq)). Their solutions all contain the hydroxide ion OH-, which gives them a characteristic set of properties.
© RM 2010. Helicon Publishing is division of RM.
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