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Which other substances can act as both acids and bases?

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sodium sulfate — acid–base reaction Sodium sulfate, also called Glauber's salt, is, like other salts, the product of an acid-base reaction.

Substances that can act as both acids and bases are described as amphoteric. These substances can donate a proton in the presence of a base and accept a proton in the presence of an acid.12

Beyond water, which is the most common example, other substances that exhibit amphoteric properties include:

Ammonia (NH₃): Can act as a base by accepting a proton to form the ammonium ion (NH₄⁺) or as an acid by donating a proton to form the amide ion (NH₂⁻).13
Amino acids: These compounds contain both acidic (–COOH) and basic (–NH₂) functional groups, allowing them to function as both acids and bases.4
Anions of polyprotic acids: Certain ions derived from acids with more than one acidic hydrogen can either lose or gain a proton. Examples include the bisulfate ion (HSO₄⁻) and phosphate ions such as the secondary phosphate ion (HPO₄²⁻).3
Metallic hydroxides: The hydroxides of zinc, aluminum, chromium, lead, and tin are also classified as amphoteric.1