Two weak acids HA and HB have same pH when their concentration ratio is 3:1. The ratio of the dissociation constants of HB and HA is ________.
pH = −log[H+]
Note: 1=HA; 2=HB
By given conditions,
pH1=pH2
−log[C1α1]=−log[C2α2]
α2α1=C1C2=3:1
So the ratio of dissociation constants of HB and HA is
K2K1=C2α22C1α21=323=3
Thus, the ratio of the dissociation constants of HB and HA is 3