The Amphoteric reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Amphoteric

Amphoteric describes something made of, or acting like, two components.

In chemistry, it indicates a substance that can react with either an acid or base. 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

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