Question

Be sure to answer all parts.Calculate the percent ionization of benzoic acid for the following concentrations:

(a) 0.40 M, (b) 0.00040 M.

Answer 1

a. Pka of benzoic acid at 25^oC is 4.2..

i.e., Ka=6.3x10-5 ; C= 0.4M =4x10^-1

ionization α = (Ka/C)^1/2 = (6.3x10-5/4x10^-1)^1/2 = (1.575x10^-4)^1/2 = 1.2x10^-2 = 0.012

%ionization = 0.012x100=1.2

b.Pka of benzoic acid at 25^oC is 4.2..

i.e., Ka=6.3x10-5 ; C= 0.00040M =4x10^-4

ionization α = (Ka/C)^1/2 = (6.3x10-5/4x10^-4)^1/2 = (1.575x10^-1)^1/2 = = (15.75x10^-2)^1/2 = 0.396

%ionization = 0.396x100=39.6

conclusion as the concentration decreases the ionization of benzoic acid increases