Alum is a type of chemical compound that is usually a hydrated double sulfate salt of aluminum with the general formula XAl(SO4)2·12H2O, where X is a monovalent cation such as potassium or ammonium. Alums are made up of water molecules, aluminum, another metal, and sulfates. They are double salts in the hydrated form and exist in different forms, such as potash alum, soda alum, ammonium alum, and chrome alum.
Alums have several properties:
- They are highly soluble in water.
- They have a sweetish taste.
- They generally crystallize in the regular octahedral form.
- The alum crystals get liquified when heated.
- They exist in the form of a white and transparent crystalline form.
Alums have various uses, including water treatment, paper sizing, and as a flocculating agent. They are also used in the production of baking powder, dyes, and fire extinguishers. The commercial uses of alums mainly stem from the hydrolysis of the aluminum ions, which results in the precipitation of aluminum hydroxide, a chemical with various industrial uses.