Question

Calculate the percent ionization of 8.0

Answer 1

Let a be the degree of ionization of the weak benzoic acid(HA)
                           HA       H ⁺ + A^-

initial conc.            c               0         0

change                -ca            ca        ca

Equb. conc.         c(1-a)         ca       ca

Dissociation constant , K_a = ca x ca / ( c(1-a)

                                         = c a² / (1-?)

In the case of weak acids ? is very small so 1-a is taken as 1

So K_a = ca²

==> a = ? ( K_a / c )

Given K_a = 1.5x10^-5

          c = concentration = 8.0x10^-3 M

Plug the values we get a = 0.0433

Therefore the percent of ionization = 0.0433 x 100 = 4.33

(2) Calculate the percent ionization of 8.0