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

Amphoteric

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

In chemistry, it means a substance that can react with either an acid or base. An example is amino acids and water. Similar many metals, such as zinc, tin, aluminium or beryllium. E.g. 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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