- A compound that can behave both as an acid
and as a base. For example, with strong
acids aluminum hydroxide acts as a base, Al(OH)3, forming
aluminum salts. With strong bases it behaves as an acid, H3AlO3,
forming salts containing the ion AlO33-. The formation
of amphoteric hydroxides is a characteristic of metalloids.
- Compounds that contain both basic and acidic functional groups. See,
for example, the amino acid glycine.