What does amphiprotic mean?
Amphiprotic is an adjective used in chemistry for a species capable of both donating and accepting a proton. Such a species can behave as a Brønsted acid when it loses a proton and as a Brønsted base when it gains one, with its behavior depending on the chemical environment. Water is the standard example: it can donate a proton to become hydroxide, OH−, or accept a proton to become hydronium, H3O+. Amino acids and hydrogen phosphate ions can also show amphiprotic behavior. The term is related to amphoteric, which is broader and describes a substance capable of acting as either an acid or a base. Amphiprotic is consequently most useful in precise discussions of proton transfer, buffer chemistry, and acid–base equilibria.
adjectiveDenoting a species that can both donate and accept a proton, and therefore behave as either a Brønsted acid or a Brønsted base.
- Capable of donating and accepting a proton, and thus behaving as either a Brønsted acid or a Brønsted base.
"The amphiprotic amino acid can donate a proton from its carboxyl group or accept one at its amino group."
"Water is amphiprotic because it can donate a proton to form hydroxide ions or accept one to form hydronium ions."
"The amphiprotic behavior of the phosphate ion depends strongly on the pH of the solution."
Some molecules play both sides in acid–base chemistry: they can hand a proton to one partner and take one from another.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does amphiprotic come from?
Amphiprotic combines Greek amphí, meaning “on both sides” or “both,” with elements related to Greek prôtos, “first,” and hence to prôton, “proton,” together with the adjectival suffix -ic. The components reflect the defining ability to act on both sides of a proton-transfer reaction by donating or accepting a proton. Its formation belongs to the same Greek-root family as amphipathic, amphipathy, and amphoteric.
Related word forms
How amphiprotic is actually used
This is a specialized chemistry term, used especially in acid–base and coordination chemistry. It is normally used attributively with words such as molecule, ion, compound, or species. The term is closely related to, but more specific than, amphoteric.
Easily confused with amphiprotic
Amphiprotic specifically describes a species that can donate and accept protons, whereas amphoteric is the broader term for a substance that can behave as either an acid or a base.