Characteristic

Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)₂. It is commonly encountered as the dodecahydrate, KAl(SO₄)₂·12H₂O. It crystallizes in cubic structure with space group P a -3 and lattice parameter of 12.18 Å. The compound is the most important member of the generic class of compounds called alums, and is often called simply alum.

Chemical formula:KAl(SO₄)₂·12H₂O

Molar mass:258.192 g/mol (anhydrous);474.37 g/mol (dodecahydrate)

Appearance:White crystals

Odor:Watery metallic

Density:1.725 g/cm³

Melting point:92 to 95 °C (198 to 203 °F; 365 to 368 K)

Boiling point:200 °C (392 °F; 473 K)

Solubility in water:14.00 g/100 mL (20 °C);36.80 g/100 mL (50 °C)

Solubility in other solvents:Insoluble in acetone

Refractive index (nD):1.4564

Application

Potassium alum is commonly used in water purification, leather tanning, dyeing, fireproof textiles, and baking powder as E number E522. It also has cosmetic uses as a deodorant, as an aftershave treatment and as a styptic for minor bleeding from shaving.