Let a be the dissociation of the weak acid
                          Â
HA <---> H + + A-
initial
conc.          Â
c             Â
0Â Â Â Â Â Â Â Â 0
change          Â
  Â
-ca          Â
+ca     +ca
Equb. conc.       Â
c(1-a)Â Â Â Â Â Â Â Â
ca     ca
Dissociation constant , Ka = ca x ca / ( c(1-a)
                                       Â
= c a2 / (1-a)
In the case of weak acids α is very small so 1-a is taken as
1
So Ka = ca2
==> a = √ ( Ka / c )
Given Ka = 7.84x10-3
         c =
concentration = 0.149 M
Plug the values we get a = 0.229
∴ % dissociation = 0.229 x 100 = 22.9
