In chemistry and physical sciences, a substance is described as amphiprotic if it can both donate or accept a proton, thus acting either like an acid or a base (according to Brønsted-Lowry theory of acids and bases: acids are proton donors and bases are proton acceptors. In Lewis theory of acids and bases; acids are electron pair acceptors and bases are electron pair donors). Water, amino acids, hydrogen carbonate ions and hydrogen sulfate ions are common examples of amphiprotic species. Since they can donate a proton, all amphiprotic substances contain a hydrogen atom. Also, since they can act like an acid or a base, they are amphoteric. Amphoteric substances, however, are not necessarily amphiprotic. For other uses, see Proton (disambiguation). ... For other uses, see Acid (disambiguation). ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... In chemistry, the Brønsted-Lowry acid-base theory or Brønsted-Lowry concept is an acid-base theory describing the reaction mechanism between acids and bases, and was independently proposed by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... This article is about the class of chemicals. ... For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... In chemistry, an amphoteric substance is one that can react with either an acid or base (more generally, the word describes something made of, or acting like, two components). ...

Example

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

HCO₃^- + H₂O → H₂CO₃ + OH^-

Or as an acid:

HCO₃^- + H₂O → CO₃^2- + H₃O⁺

Thus, it can effectively accept or donate a proton. Water is the most common example of an amphiprotic substance:

Basic: H₂O + HCl → H₃O⁺ + Cl^-

Acidic: H₂O + NH₃ → NH₄⁺ + OH^-