Alum

Alum ( /ˈæləm/) 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(SO4)2·12H2O. More widely, alums are double sulphate salts, with the formula AM(SO4)2·12H2O, where A is a monovalent cation such as potassium or ammonium and M is a trivalent metal ion such as aluminium or chromium(III).

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