What is a conjugate base?

  • The concept of conjugate acids and bases arise from the Bronsted-Lowry acid-base theory
  • When an acid (HA) dissociates into its ions in a solvent it loses a hydrogen ion (H+)
  • The species that is formed is the “conjugate” base of the acid (A–) – it is a base as it is able to absorb the hydrogen ion that has been lost
  • The reaction can be summarised as:
Dissociation of acid into conjugate base and Hydrogen ion
  • Examples of commonly encountered acids and their conjugate bases include:
Acid
(HA)
Conjugate Base
(A-)
Hydrochloric Acid
HCl
Chloride Ion
Cl-
Carbonic Acid
H2CO3
Bicarbonate Ion
HCO3-
Lactic Acid
C3H6O3
Lactate Ion
C3H5O3-