Question

What is the pH of a 0.02M solution of potassium benzoate solution ( K+ -OOCC6H5). The pka of benzoic acid is 4.19. (Write answer to the hundredths place)

Answer 1

Let's call benzoic acid HBz so potassium benzoate is KBz. It is the Bz^- that is hydrolyzed and the pH is determined by that hydrolysis.
................Bz^- + HOH ==> HBz + OH^-
I..............0.02M.....................0.............0
C..............-x...........................x..............x
E..............0.02-x....................x...............x

Kb for Bz^- = (Kw/Ka for HBz) = (HBz)(OH^-)/(Bz^-)
Plug in Kw, Ka(from pKa), the E line for HBz, OH^-, Bz^- and solve for x = (OH^-) and convert to pH. Post your work if you get stuck.