In chemistry, a substance is described as amphiprotic, if it can both donate or accept a proton, thus acting either like an acid or a base. An example are amino acids. See also amphoteric. Water, hydrogen carbonate ions and hydrogen sulfate ions are common examples of amphiprotic species. One distinguishing feature is that amphiprotic substances contain a hydrogen ion.

Example

A common example is the hydrogen carbonate ion, which can act as a base:

HCO₃^- + H₃O⁺ → H₂CO₃ + H₂O

Or as an acid:

HCO₃^- + H₂O → CO₃^2- + H₃O⁺

Effectively making it able to accept or donate a proton (hydrogen ion).