Phosphate can act as buffer: H2PO4- HPO4^2- + H+

The pKa of this equilibrium is 7.21. What is the ratio of H2PO4-
to HPO4^2- at pH 7.0?
A. 1.62
B. 0.62
C. 50.47
D. 0.019
E. 0.21

1 answer

The HH equation calculates this directly.