CONJUGATE ACIDS AND BASES REVISITED
As mentioned above, a conjugate acid is defined as the acid formed when a base gains a proton.
Similarly, a conjugate base is formed when an acid loses a proton. For example, in the acetic
acid/acetate conjugate acid/base pair CH 3 COOH/CH 3 COO− (also written as HC 2 H 3 O 2 /C 2 H 3 O 2 −
although the former gives more structural information about the molecule), CH 3 COO− is the
conjugate base and CH 3 COOH is the conjugate acid:
CH 3 COOH (aq) H+ (aq) + CH 3 COO− (aq)or:
CH 3 COOH (aq) + H 2 O (l) H 3 O+ (aq) + CH 3 COO− (aq)Likewise, for the Kb of CH 3 COO−:
CH 3 COO− (aq) + H 2 O (l) CH 3 COOH (aq) + OH− (aq)The equilibrium constants for these reactions are as follows:
and
Adding the two reactions shows that the net reaction is simply the dissociation of water:
H 2 O (l) H+ (aq) + OH− (aq)