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Alkali. Any base or any hydroxide of an alkali metal or of ammonium that yields hydroxyl ions (OH-) in aqueous solutions, neutralizes acids (q.v.) to form salts, and turns red litmus paper (q.v.) blue. Common examples of this group of compounds include sodium and potassium carbonates, which are salts that do not undergo extensive dissociation (q.v.) when in solution and thus represent mild alkalis, and sodium hydroxide (caustic soda) and potassium hydroxide (caustic potash) which, because of their high degree of dissociation (q.v.), are strong alkalis. Aqueous solutions of alkali salts, because of the predominant presence of hydroxyl ions, exhibit pH (q.v.) values that are higher than 7.