Aluminium hydroxide - Al(OH)3

What is Aluminium hydroxide?

Al(OH)3 is amphoteric in nature with chemical name Aluminium hydroxide. It is also called Aluminic acid or Aluminic hydroxide or Aluminium (III) hydroxide. It is found in nature in the form of mineral gibbsite and its polymorphs viz doyleite, nordstrandite, and bayerite.

Aluminic hydroxide is an amorphous powder white in colour. It is insoluble in water but soluble in alkaline and acidic solutions.

Properties of Aluminium hydroxide – Al(OH)3


Aluminium hydroxide

Molecular weight of Al(OH)3

78.00 g/mol

Density of Aluminium hydroxide

2.42 g/dm3

Flash point of Aluminium hydroxide


Melting Point of Aluminium hydroxide

300 °C

Aluminium hydroxide structure – Al(OH)3

Aluminium hydroxide structure

Aluminic hydroxide has a typical structure of metal hydroxide consisting of hydrogen bonds. It comprises of double layers of hydroxyl groups along with aluminium ions which occupy 2/3rd of the octahedral holes which are formed between the two layers.

Gibbsite is amphoteric and acts as a Bronsted-Lowry base to yield a salt by by picking up hydrogen ions and neutralizing the acid. The reaction is as follows:

3HCl + Al(OH)3 → AlCl3 + 3H2O

It acts as a Lewis acid in bases. It takes away an electron pair from the hydroxide ions. The re4action is as follows:

Al(OH)3 + OH → Al(OH)4

Al(OH)3 Uses (Aluminium hydroxide)

  • Aluminium hydroxide is used as a flame retardant in plastics.
  • Used as an antacid.
  • Used in aluminum Hydroxide gel.
  • Used to manufacture activated alumina.
  • Used as filler in cosmetics.
  • Used as a chemical intermediate.
  • Used as a soft abrasive for plastics.
  • Used in glass additive to increase resistance to thermal shock.
  • Used in waterproofing fabrics.
  • Used in the manufacturing of glass.

Production of Aluminium hydroxide

Commercially used aluminium hydroxide is manufactured by Bayer process. It is carried out by dissolving bauxite in sodium hydroxide solution at a temperature range up to 270 °C. The waste is removed and the sodium aluminate solution is allowed to precipitate. Therefore the precipitate obtained is aluminium hydroxide. Alumina or aluminium oxide can be obtained from aluminium hydroxide by the process of calcination.

Health hazards

Prolonged exposure to Aluminium(III) hydroxide it causes irritation in eyes, respiratory system, and skin. When comes in contact with water it causes violent explosion.

Learn more about the Structure, physical and chemical properties of Al(OH)3 from the experts at BYJU’S.

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