Chapter 16.6, Problem 16.13WE

Aspirin (acetylsalicylie acid, HC₉H₇O₄) is a weak acid. It ionizes in water according to the equation

${\text{HC}}_{\text{9}}{\text{H}}_{\text{7}}{\text{O}}_{\text{4}}\left(aq\right)+{\text{H}}_{\text{2}}\text{O}\left(l\right)\rightleftarrows {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\left(aq\right)+{\text{C}}_{\text{9}}{\text{H}}_{\text{7}}{\text{O}}_{\text{4}}^{-}\left(aq\right)$

A 0.10-M aqueous solution of aspirin has a pH of 2.27 at 25°C. Determine the K_a of aspirin.