Percent Dissociation

$% d i ssoc ia t i o n = \frac{[ H 3 O + ]}{[ H A ]}$
Equilibrium constant determines results

Example

$H A + H_{2} O ⇌ A^{-} + H_{3} O^{+}$

	$H A$	$H_{2} O$	$A^{-}$	$H_{3} O^{+}$
Initial	1.0 M	Excess	0 M	0 M
Change	-0.2 M	N/A	+0.2 M	+0.2 M
Equilibrium	0.8 M	N/A	0.2 M	0.2 M

$% d i ssoc ia t i o n = \frac{0.2 M}{1.0 M} = 20%$