Aluminium hydroxide

Aluminium hydroxide, Al(OH)₃, is the most stable form of aluminium in normal conditions. As found in nature it is known as the mineral gibbsite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide, Al₂O₃, differing only by loss of water. These compounds together are the major components of the aluminium ore, bauxite.

The character of 'aluminium hydroxide' has been controversial. It is safe to say that a simple scheme of Al³⁺ ions and OH^- ions is oversimplified. More and less hydrated forms are very common. Some people write Al₂O₃.xH₂O instead.

Aluminium hydroxide is amphoteric. In strongly acid conditions, Al(OH)₂⁺ is formed; in strongly basic conditions, Al(OH)₄^- is formed. These are the main ions in dilute solutions; in concentrated solutions, polymeric ions are formed which can be quite complex.

Salts of the anion Al(OH)₄^- (or similar, such as AlO₂^-) are sometimes called aluminates.

Al(OH)₃ has a molar mass of 78.01.

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