Caustic soda is one of the common names for sodium hydroxide (NaOH), which is also known as lye. Its common name derives from its chemical identity as a sodium hydrate and because it is caustic or corrosive. In pure form, caustic soda is a waxy, white solid. It readily absorbs water and forms aqueous solutions. Commercially available caustic soda or sodium hydroxide is usually sodium hydroxide monohydrate, NaOH·H2O.
