Brønstedzuren

Brønstedzuren are acids according to the Brønsted–Lowry theory. An acid is a substance that donates a proton (H+) to a base during an acid–base reaction. In a typical process, a Brønsted acid HA transfers a proton to a base B, yielding the conjugate base A− and the conjugate acid BH+. In aqueous solution this often means HA donates a proton to water, forming H3O+ and A−. Brønsted bases are proton acceptors, and the concept of conjugate acid–base pairs follows: every Brønsted acid has a conjugate base, and every Brønsted base has a conjugate acid.

Common Brønsted acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3) and acetic acid (CH3COOH). The strength of a Brønsted acid is described by the acid dissociation constant Ka. Strong Brønsted acids dissociate almost completely in water (large Ka), while weak Brønsted acids dissociate only partially (smaller Ka). Many Brønsted acids are polyprotic, capable of donating more than one proton in successive steps, each with its own pKa value, as seen in sulfuric, phosphoric, and carbonic acids.

The measured acidity, including pKa values, depends on the solvent; pKa in water differs from that in nonaqueous solvents. In general, acidity conceptually links to conjugate bases: a stronger acid has a weaker conjugate base.

Relation to other theories: every Brønsted acid is a Lewis acid (it donates a proton, i.e., a Lewis acid site), but not every Lewis acid must function as a Brønsted acid. Brønsted acids are foundational in acid–base chemistry, influencing reactions, titrations, and buffer design in chemistry and biology.