Conjugate Acid–Base Pair
Two species differing by exactly one proton, one being the acid and the other its corresponding base.
Formula / equation
HA / A⁻
Unit
Dimensionless
In depth
Removing a proton from an acid gives its conjugate base; adding one to a base gives its conjugate acid. Strength is inversely related within a pair: a strong acid has a very weak conjugate base, which is why the chloride ion has no measurable basicity.
Examples in the real world
HCl/Cl⁻, CH₃COOH/CH₃COO⁻, and NH₄⁺/NH₃; water pairs with both H₃O⁺ and OH⁻.