What type of oxide is aluminium oxide (Al₂O₃)?

Aluminium oxide (Al₂O₃) is an example of an amphoteric oxide, which means it can behave as both an acidic oxide and a basic oxide depending on the reacting substance. This dual property comes from the intermediate position of aluminium in the periodic table, lying between metals and nonmetals. Amphoteric behavior is a common characteristic of oxides of elements near the metalloid boundary.

When aluminium oxide reacts with acids like hydrochloric acid (HCl), it shows basic properties because it neutralizes the acid and forms salts such as aluminium chloride (AlCl₃) and water:

Al2O3+6HCl→2AlCl3+3H2OAl_2O_3 + 6HCl → 2AlCl_3 + 3H_2OAl2O3+6HCl→2AlCl3+3H2O

However, when aluminium oxide reacts with strong bases like sodium hydroxide (NaOH), it behaves as an acidic oxide and forms sodium aluminate (NaAlO₂):

Al2O3+2NaOH→2NaAlO2+H2OAl_2O_3 + 2NaOH → 2NaAlO_2 + H_2OAl2O3+2NaOH→2NaAlO2+H2O

This amphoteric behavior makes aluminium oxide a key compound in both laboratory and industrial chemistry. It is used as a catalyst support, in ceramics, and as an abrasive due to its hardness and thermal stability. In nature, aluminium oxide occurs as the mineral corundum, which is the base form of gemstones like ruby and sapphire.

The oxide’s chemical stability and insolubility in water also make it important in materials science and corrosion resistance. Understanding amphoteric oxides helps explain the transition between metallic and nonmetallic chemical behavior within the periodic table