Question

Equal volumes of 0.120 M weak base (Kb = 5.0× 10–9) and 0.120 M HCl are mixed. Calculate the pH of the resulting solution.

Answer 1

if both are equal volume

then 0.12 / 2 = 0.06 M salt will form

it is a salt of weak base and strong acid.

for such salts   pH = 1/2 (pKw - pKb - log C)

                   Kb = 5.0 x 10^-9

                   pKb = -log (5.0 x 10^-9)

                    pKb = 8.3

                    pH = 1/2 (14 - 8.3 - log 0.06)

                    pH = 3.46