A diprotic or polyprotic buffer can be approached in a way similar to monoprotic buffers. The key difference is that multiple pKa values will be involved.
Diprotic & Polyprotic Buffers
Concept #1: Diprotic & Polyprotic Buffers
Concept #2: Diprotic & Polyprotic Buffers
Concept #3: Diprotic & Polyprotic Buffers
Example #1: Calculate the pH of 100 mL of a 0.25 M H2CO3 when 70.0 mL of 0.25 M NaOH are added. Ka1 = 4.3 x 10-7 and Ka2 = 5.6 x 10-11.
Example #2: Calculate the pH of 75.0 mL of a 0.10 M of phosphorous acid, H3PO3, when 80.0 mL of 0.15 M NaOH are added. Ka1 = 5.0 x 10-2, Ka2 = 2.0 x 10-7.