I dont get this....You have a solution that is buffered at pH= 2.0?

Question

using H3PO4, and H2PO4 ^- . You decid to titrate this buffer with a strong base. 15 mL are needed to reach the 1st equivalence point. What is the total volume of base that will have been added when the 2nd equivalence point is reached?

why would it be > 30mL?

Answer 1

Because it's twice 15ml.  You are titrating the H+ and each of the H+'s on the phosphate requires the same amount of base.

Answer 2

The equilibrium constant is more to produce HPO42- and still more for PO43-