Question

What volume of 1.0 M of NaOH (in mL) is needed to reach the second equivalence point when titrating 100 mL of 0.12 M phosphoric acid?

Answer 1

Answer:The example below should illustrate these points. We will plot the titration of

100 mL of 0.10 M phosphoric acid with 1.0 M NaOH.

H3PO4 + H2O  H2PO4

-

+ H3O+

Ka1 = 7.5 x 10-3

H2PO4

-

+ H2O  HPO4

2- + H3O+

Ka2 = 6.2 x 10-8

HPO4

2- + H2O  PO4

3- + H3O+

Ka3 = 4.2 x 10-13

Explanation: