Alum
Alum /ˈælum/ is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate (potassium alum) with the formula KAl(SO
4)2·12H
2O. More widely, alums are double sulfate salts, with the general formula AM(SO
4)
2·12H
2O, where A is a monovalent cation such as potassium or ammonium and M is a trivalent metal ion such as aluminium or chromium(III). When the trivalent ion is aluminium, the alum is named after the monovalent ion.
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