Question

What is the hydronium ion concentration of a 1.98x10^-4 M  solution of p-bromobenzoic acid, , for which Ka= 1.00x10^-4 ?

Answer 1

Ka = 1.00 x 10^-4

concentration = 1.98 x 10^-4 M

HA +   H2O   ---------------->   HA-   + H3O+

1.98 x10^-4                            0            0

1.98x10^-4 - x                        x            x

Ka = x^2 / 1.98x10^-4 - x    

1.00x10^-4 = x^2 / 1.98x10^-4 - x    

x = 9.93 x 10^-5

[H3O+] = 9.93 x 10^-5 M