The equilibrium equation showing the dissociation of weak acid is:
[tex] HA (aq) + H_{2}O(l) <==> A^{-}(aq) + H_{3}O^{+}(aq) [/tex]
[tex] K_{a} [/tex] is the equilibrium constant for this equation, which is referred to as the acid dissociation constant. [tex] K_{a} [/tex] value will determine the acidic strength of the acids. Greater the value, more will be the acidity.
Calculating the [tex] K_{a} [/tex] value from given equilibrium concentrations:
[tex] K_{a} = \frac{[H_{3}O^{+}][A^{-}]}{[HA]} [/tex]
= [tex] \frac{(2.00*10^{-4})(2.00*10^{-4})}{0.220} [/tex]
= [tex] 1.82 * 10^{-7} [/tex]
