Amphoteric substances aluminum oxide

Metals typically form basic oxides and nonmetals typically form acidic oxides, but what about the elements that lie on the diagonal frontier between the metals and nonmetals Along this frontier from beryllium to polonium, metallic character blends into nonmetallic character, and the oxides of these elements have both acidic and basic character (Fig. 10.7). Substances that react with both acids and bases are classified as amphoteric, from the Greek word for both. For example, aluminum oxide, A1203, is amphoteric. It reacts with acids ... 

In the two equations above, notice that water is acting as an acid in one instance and as a base in the other. Substances like water that can act as an acid or a base depending on the circumstances are called amphoteric substances. The word comes from the Greek prefix ampho-, which means both. Water is the most common amphoteric substance, but amino acids, proteins, and some metal oxides—such as aluminum oxide (Al203) and zinc oxide (ZnO), for example—can also act as amphoteric substances. 

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