Aluminium hydroxide, with the chemical formula Al(OH)3, is a chemical compound composed of aluminium (Al) and hydroxide ions (OH-). It is an inorganic compound and is commonly encountered as a white or off-white gelatinous solid.

Aluminium hydroxide is an amphoteric compound, meaning it can act as both an acid and a base. It has several important properties and uses, including:

1. Antacid: Aluminium hydroxide is widely used as an antacid medication to treat heartburn, acid indigestion, and upset stomach. When ingested, it neutralizes excess stomach acid by reacting with the hydrochloric acid in the stomach, forming water and aluminium chloride.
2. Phosphate Binder: Aluminium hydroxide is used in some medical applications as a phosphate binder to reduce phosphate levels in patients with kidney disease.
3. Water Purification: Aluminium hydroxide is employed in water purification processes as a flocculant to remove suspended particles and impurities from water.
4. Flame Retardant: In some applications, aluminium hydroxide is used as a flame retardant, as it can release water when exposed to high temperatures, helping to reduce the spread of fire.
5. Filler in Plastics: Aluminium hydroxide is added to some plastics as a filler to improve their mechanical properties and flame resistance.
6. Gelatinous Precipitate: Aluminium hydroxide can form a gelatinous precipitate when reacting with alkaline substances or bases, which is used in qualitative analysis and in some chemical processes.

Due to its medicinal and industrial applications, aluminium hydroxide is an essential compound in various fields, including medicine, water treatment, and materials science. As with any compound, proper safety precautions should be taken when handling aluminium hydroxide to prevent potential hazards.