Ka and Ka2

[CHEM 14B Lover]

Will be asked to find pH given Ka and Ka2 of a diprotic acid? How would we set up an ice tablee in that case?

[David S]

You first set up ice table and Ka expression for the diprotic acid, and then you solve for [H+]and [HA-]. You then set up separate ice table and Ka2 expression for the dissociation of HA- into A2- and H+ using the [H+] and [HA-] found in part 1. Solve for new [H+] and then turn it into pH.

Note that usually the second and third dissociation s add very little H+ to the H+ formed by first dissociation.