Conjugate Acid-Base Pair
Definition and meaning of Conjugate Acid-Base Pair in chemistry.
A conjugate acid-base pair is a set of two chemical species that differ from each other by exactly one proton (H⁺): the acid, which donates the proton, and its conjugate base, which is what remains after the proton is lost.
In more detail
This concept comes from the Brønsted-Lowry theory of acids and bases, in which acid-base reactions are proton-transfer reactions. Every such reaction involves two conjugate pairs: the acid transfers a proton to a base, generating the conjugate base of the first species and the conjugate acid of the second. There is an inverse relationship in strength within a pair, a strong acid has a weak conjugate base, and a weak acid has a relatively stronger conjugate base, which underlies buffer behavior and equilibrium calculations.
Key facts
| Field | General Chemistry |
|---|---|
| General form | HA (acid) / A⁻ (conjugate base) |
| Defining feature | Differ by exactly one H⁺ |
| Strength trend | Stronger acid ⇒ weaker conjugate base |
Acetic acid (CH3COOH) and the acetate ion (CH3COO⁻) are a conjugate acid-base pair: CH3COOH donates a proton to water, becoming CH3COO⁻, while water accepts the proton to become its conjugate acid, H3O⁺.
Frequently asked questions
How do you spot a conjugate acid-base pair in a reaction?
Find two species on opposite sides of the equation that differ by only one H⁺; the species with the extra proton is the acid, and the one without it is its conjugate base.