Alum

Family of double sulfate salts of aluminium

An alum is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula XAl(SO4)2·12 H2O, such that X is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, with the formula KAl(SO4)2·12 H2O. Other alums are named after the monovalent ion, such as sodium alum and ammonium alum.

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