Phenylacetic Acid Is One of the Substances That Accumulates in the Blood

Multiple Choice

Phenylacetic acid is one of the substances that accumulates in the blood of persons with phenylketonuria, an inherited disorder that can cause mental retardation or even death. A 0.085 M solution of this substance is found to have a pH of 2.68. What is the acid ionization constant , K _a, for this acid?

A) K _a = 5.0×10 ^{- 5}
B) K _a = 5.3×10 ^{- 5}
C) K _a = 2.1×10 ^{- 3}
D) K _a = 2.5×10 ^{- 2}
E) K _a = 5.0×10 ^{- 2}