Chapter 14, Problem 116E

The indicator dinitrophenol is an acid with a K_a of $1.1\times {10}^{-4}$. In a $1.0\times {10}^{-4}$ -M solution, it is colorless in acid and yellow in base. Calculate the pH range over which it goes from 10% ionized (colorless) to 90% ionized (yellow).