Aluminum Compounds

Although it does not seem to be particularly reactive, aluminum is considered an active metal. Its behavior is deceptive because it reacts rapidly with the oxygen in the air to form aluminum oxide (Al₂O₃), or alumina, which is tightly bound to the metal and exists as a dense coating (unlike the oxides of iron). This coating protects it from further reaction. Clearly, however, this coating is not entirely foolproof since aluminum does not exist in native form.

Alumina is the refractory oxide of aluminum and is found in bauxite and corundum (sapphires and rubies). It has a very high melting point. One of the applications of this compound is used to produce different color light that can be used as a laser beam. It is also used in pottery, dyeing, antacid medicines, and in making chemicals.

Another compound containing aluminum is Al(OH)₃, which is usually formed as a gelatinous precipitate when aluminum compounds are hydrolyzed in water.

Aluminum sulfate, Al₂(SO₄)₃·18H₂O is a very useful aluminum compound, made from the oxide and sulfuric acid. One use of this salt is in the dyeing of cotton fabrics.