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(SO
4)₂·12H
2O. More widely, alums are double sulfate salts, with the general formula A
2(SO
4).M
2(SO
4)
3.24H
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.

Chemical properties

Alums are useful for a range of industrial processes. They are soluble in water; have a not sweetish taste; react acid to litmus; and crystallize in regular octahedra. When heated they liquefy; and if the heating is continued, the water of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains. They are astringent and acidic.

Uses

Industrial uses

Potassium alum is the common alum of commerce, although soda alum, ferric alum, and ammonium alum are manufactured.

Alum (disambiguation)

Alum is a species and class of chemical compound.

Alum may also refer to:

See also

Alum (surname)

Alum is a surname. Notable people with the surname include:

See also