Answer
The concentration of acetic acid in equilibrium in vinegar is = 0.05556M.
Work Step by Step
1. Find the $[H_3O^+]$ value:
$[H_3O^+] = 10^{-pH}$
$[H_3O^+] = 10^{- 3}$
$[H_3O^+] = 1 \times 10^{- 3}$
2. Drawing the equilibrium (ICE) table we get these concentrations at equilibrium:** The image is in the end of this answer.
-$[H_3O^+] = [Acetate] = x$
3. Now, use the Ka and x values and equation to find the initial concentration value.
$Ka = \frac{[H_3O^+][Acetate]}{ [Acetic acid]}$
$ 1.8\times 10^{- 5}= \frac{[x^2]}{ [Acetic acid]}$
$ 1.8\times 10^{- 5}= \frac{( 1\times 10^{- 3})^2}{[Acetic acid]}$
$[Acetic acid]= \frac{ 1\times 10^{- 6}}{ 1.8\times 10^{- 5}}$
$[Acetic acid] = 0.05556$
