0Toga_Dan 3 years ago Alum/ˈælum/ is both a specificchemical compound and a class of chemical compounds. The specific compound is the hydratedpotassiumaluminiumsulfate (potassium alum) with the formulaKAl(SO4)2·12H2O. More widely, alums are double sulfate salts, with the general formula AM(SO4)2·12H2O, where A is a monovalent cation such as potassium or ammonium and M is atrivalent metal ion such as aluminium orchromium(III). When the trivalent ion is aluminium, the alum is named after the monovalent ion. Lifted from wiki.