Conjugate Acid Definition

Conjugate Acid-Base Pairs

A conjugate acid is formed when a base gains a hydrogen or proton.
A conjugate acid is formed when a base gains a hydrogen or proton. Jutta Klee / Getty Images

Conjugate Acid Definition

Conjugate acids and bases are Bronsted-Lowry acid and base pairs, determined by which species gains or loses a proton. When a base dissolves in water, the species that gains a hydrogen (proton) is the base's conjugate acid.

Acid + Base → Conjugate Base + Conjugate Acid

In other words, a conjugate acid is the acid member, HX, of a pair of compounds that differ from each other by gain or loss of a proton.

A conjugate acid can release or donate a proton.

Conjugate Acid Example

When the base ammonia reacts with water, the ammonium cation is the conjugate acid that forms:

NH3(g) + H2O(l) → NH+4(aq) + OH(aq)

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Helmenstine, Anne Marie, Ph.D. "Conjugate Acid Definition." ThoughtCo, Jul. 13, 2017, thoughtco.com/definition-of-conjugate-acid-605846. Helmenstine, Anne Marie, Ph.D. (2017, July 13). Conjugate Acid Definition. Retrieved from https://www.thoughtco.com/definition-of-conjugate-acid-605846 Helmenstine, Anne Marie, Ph.D. "Conjugate Acid Definition." ThoughtCo. https://www.thoughtco.com/definition-of-conjugate-acid-605846 (accessed May 24, 2018).