Practice: 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 × 10−2, Ka2 = 2.0 × 10−7.
Concept #1: Diprotic Buffers
Diprotic Buffers: have 2 equivalence points and as a result, have 2 Ka values.
Example #1: Calculate the pH of 100 mL of a 0.250 M H2CO3 when 120.0 mL of 0.250 M NaOH are added. Ka1 = 4.3 x 10-7 and Ka2 = 5.6 x 10-11.
Concept #2: Polyprotic Buffers
Polyprotic Buffers: have 3 equivalence points and as a result, have 3 Ka values.
Example #2: Calculate the pH of 30.0 mL of a 0.10 M H3C6H5O7 when 50.0 mL of 0.20 M NaOH are added. Ka1 = 7.4 x 10-4, Ka2 = 1.7 x 10-5 and Ka3 = 4.0 x 10-7.
Practice: 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 × 10−2, Ka2 = 2.0 × 10−7.
Practice: Find the pH when 100.0 mL of a 0.1 M dibasic compound B (pKb1 = 4.00; pKb2 = 8.00) was titrated with 11 mL of a 1.00 M HCl.
Practice: Suppose you have 50.1 mL of a H3PO4 solution that you titrate with 15.4 mL of 0.10 M KOH solution to reach the endpoint. What is the concentration of H3PO4 of the original H3PO4 solution?
