Solving Biochem pH Problem for Na2HPO4 Solution

[vcuram]

Homework Statement

Solid Na2HPO4 is dissolved in water. What is the resulting pH of the solution? Relative pka's of phosphate derivaties are ~2, ~7, and ~12.

Homework Equations

No equation needed, just look at the species which phosphate would develop.

The Attempt at a Solution

I believe the specified compound would be in equilibrium between one of these species;
H3PO4, H2PO4 (-), HPO4 (-2) and PO4 (-3). The choices are 12, 7, 2, 9, or there is not enough information.

 

[Borek]

pH of amphiprotic salt solution

 

[vcuram]

Thank you very much! If I understand correctly then the answer would be 1/2 (7 +12) which would be ~ 9 ph?

That is the answer I chose. Thank you.