Your Friend at Podunk U

Multiple Choice

Your friend at Podunk U. urgently emails asking if you remember any acid-base chemistry. His problem is that for his final organic lab problem he needs to report the pK_a of his acid. He did the pH titration, but only wrote down the following data for the titratant volumes: V = 14.27 mL; pH = 4.73. V_{equivalence point} = 22.43 mL. What is the pK_a of the unknown acid?

A) 3.5
B) 4.0
C) 4.5
D) 4.8
E) 4.9