In the Titration of 25

Multiple Choice

In the titration of 25.0 mL of a solution of a weak acid HX with 0.250 M NaOH, the pH = 4.50 after the addition of 5.0 mL of the NaOH solution. The equivalence point occurs when 30.4 mL of the NaOH solution has been added. What is the ionization constant ( K _a) of HX?

A) 1.4×10 ^{- 5}
B) 3.2×10 ^{- 5}
C) 6.2×10 ^{- 6}
D) 3.2×10 ^{- 10}
E) 7.2×10 ^{- 10}