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In chemistry, a compound classed as a base that is soluble in water. Alkalis neutralize acids and are soapy to the touch.
The hydroxides of metals are alkalis: those of sodium (sodium hydroxide, NaOH) and of potassium (potassium hydroxide, KOH) being chemically powerful; both were 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.
Alkalis react with acids to form a salt and water (neutralization).
KOH + HNO3 ® KNO3 + H2O
OH- + H+ ® H2O
They give a specific color reaction with indicators; for example, litmus turns blue.
A mixture of soluble salts found in arid soils and some bodies of water; detrimental to agriculture.