What is the ph of a solution that is 0.06 m in sodium benzoate (nac7h5o2) and 0.09 m in benzoic acid (hc7h5o2)?

To determine the pH of a solution which has 0.06 m in sodium benzoate (nac7h5o2) and 0.09 m in benzoic acid (hc7h5o2), we use the ICE table and the acid dissociation constant of hc7h5o2 to determine the concentration of the hydrogen ion present at equilibrium. We do as follows:

HC7H5O2 = H+ + C7H5O2-
NaC7H5O2 = Na+ + C7H5O2-

Therefore, the only source of hydrogen ion would be the acid. We use the ICE table,
                   HC7H5O2           H+        C7H5O2-
I                     0.09                  0              0.06
C                      -x                    +x               +x

E                 0.09-x                x              0.06+ x

Ka = 6.28x10^(-5) = (0.06 + x) (x) / 0.09 -x 
x = 9.40x10^-5 M = [H+]

pH = - log [H+] 
pH = -log  9.40x10^-5 M
pH = 4.03

Therefore, the pH of the resulting solution would be 4.03.