Amphoteric Definition and Examples

An amphoteric substance is one that can act as either an acid or a base, depending on the medium. The word comes from the Greek amphoteros  or amphoteroi, meaning each or both of two and, essentially, either acid or alkaline. Amphiprotic molecules are a type of amphoteric species that either donates or accepts a proton (H), depending on the conditions. Not all amphoteric molecules are amphiprotic. For example, ZnO acts as a Lewis acid, which can accept an electron pair from OH but cannot donate a proton. Ampholytes are amphoteric molecules that exist primarily as zwitterions over a given pH range and have both acidic groups and basic groups. Here are some 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.