Aluminium potassium sulfate, also known as potassium alum or alum, is a chemical compound with the chemical formula KAl(SO4)2·12H2O. It is an ionic compound composed of potassium (K), aluminium (Al), sulfate ions (SO4^2-), and water molecules (H2O). It belongs to the family of double sulfates.

Aluminium potassium sulfate is commonly encountered as colorless or white crystals or powder. It is highly soluble in water and has various uses and properties, including:

1. Traditional Use as a Mordant: Historically, potassium alum was widely used as a mordant in the textile industry to fix dyes to fabrics, improving colorfastness.
2. Food Additive: Potassium alum is used as a food additive, particularly in the production of pickles and certain types of baking powder, where it acts as a leavening agent.
3. Medicinal and Cosmetic Uses: In some traditional medicine practices, potassium alum has been used for its astringent and antiseptic properties. It is also used in cosmetic products as an ingredient in certain deodorants and aftershaves.
4. Water Treatment: Potassium alum is used in some water treatment processes as a coagulant to remove impurities and suspended particles from water.
5. Flame Retardant: Potassium alum is used as a flame retardant in some applications to reduce the flammability of materials.

It’s important to note that while potassium alum has various uses and applications, it should be used in accordance with relevant safety guidelines and regulations. In some cases, its use as a food additive or in cosmetic products may be subject to specific regulations and restrictions by health authorities. As with any chemical compound, proper handling and safety precautions should be followed to ensure safe use.