Answer
$\frac{[CH_3COO^-]}{[CH_3COOH]} = 0.56$
Work Step by Step
1. Calculate $[H_3O^+]$:
$[H_3O^+] = 10^{-pH}$
$[H_3O^+] = 10^{- 4.5}$
$[H_3O^+] = 3.2 \times 10^{- 5}$
2. Write the $K_a$ equation, and find the ratio:
$K_a = \frac{[H_3O^+][CH_3COO^-]}{[CH_3COOH]}$
$1.8 \times 10^{-5} = \frac{3.2 \times 10^{-5}*[CH_3COO^-]}{[CH_3COOH]}$
$\frac{1.8 \times 10^{-5}}{3.2 \times 10^{-5}} = \frac{[CH_3COO^-]}{[CH_3COOH]}$
$0.56 = \frac{[CH_3COO^-]}{[CH_3COOH]}$
