Why do we add alum to purify water?
Chemical formula of alum is KAl(SO4)2 known as Potassium aluminium sulphate.In raw water, bicarbonate salts are present as impurities. Alum, when added react with alkaline bicarbonates and forms a gelatinous precipitate. This also attracts other fine and suspended particles and settled down at the bottom of the container. In this way we can get purified water.