A Phosphate Buffer Solution (25

Multiple Choice

A phosphate buffer solution (25.00 mL sample) used for a growth medium was titrated with 0.1000 M hydrochloric acid. The components of the buffer were sodium monohydrogen phosphate and sodium dihydrogen phosphate. The first endpoint occurred at a volume of 10.32 mL; the second occurred after an additional 18.62 mL was added, for a total volume of 28.94 mL. What was the approximate ratio of HPO₄^2- to H₂PO₄^- in the buffer?

A) 1:1
B) 4:5
C) 5:3
D) 5:4
E) 3:5