Amphoteric Definition and Examples

What Amphoteric Means in Chemistry

Illustration of molecule in water
Self-ionizing compounds, such as water, are examples of amphoteric molecules which are also amphiprotic. Yuji Sakai/Getty Images

An amphoteric substance is one which can act as either an acid or a base, depending on the medium. The word comes from Greek amphoteros or amphoteroi or "each or both of two", essentially meaning "either acid or alkaline".

Amphiprotic molecules are a type of amphoteric species that either donate or accept a proton (H+), depending on the conditions. Not all amphoteric molecules are amphiprotic. For example, ZnO acts as a Lewis acid and can accept an electron pair from OH, but it cannot donate a proton.

Ampholytes are amphoteric molecules that exist primarily as zwitterions over a given pH range and that have both acidic groups and basic groups.

Examples of Amphoterism

  • Metal oxides or hydroxides are amphoteric. Whether a metal compound acts as an acid or a base depends on the oxide oxidation state.
  • Sulfuric acid (H2SO4) is an acid in water, but is amphoteric in superacids.
  • Amphiprotic molecules, such as amino acids and proteins, are amphoteric.
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Helmenstine, Anne Marie, Ph.D. "Amphoteric Definition and Examples." ThoughtCo, May. 4, 2017, Helmenstine, Anne Marie, Ph.D. (2017, May 4). Amphoteric Definition and Examples. Retrieved from Helmenstine, Anne Marie, Ph.D. "Amphoteric Definition and Examples." ThoughtCo. (accessed May 25, 2018).