Amphoteric

In chemistry, an amphoteric substance is one that can react with either an acid or base (more generally, the word describes something made of, or acting like, two components).

Examples include amino acids and water. Many metals, such as zinc, tin, aluminium and beryllium, have amphoteric oxides. For example, zinc oxide ZnO reacts differently depending on the pH of the solution:

In acids:

ZnO + 2H⁺ → Zn²⁺ + H₂O

In bases:

ZnO + H₂O + 2OH^- → [Zn(OH)₄]^2-

This effect can be used to separate different cations, such as zinc from manganese.

See also:

• amphiprotic
• ampholytic