We’re being asked to calculate the pH of a solution that is 0.242 M C_{6}H_{5}COOH and 0.183 M C_{6}H_{5}COONa.

In this case, we will be using the Henderson-Hasselbalch equation which can be used for buffer solutions

Recall the Henderson-Hasselbalch equation:

$\overline{){\mathbf{pH}}{\mathbf{=}}{{\mathbf{pK}}}_{{\mathbf{a}}}{\mathbf{+}}{\mathbf{log}}\left(\frac{\mathbf{conjugate}\mathbf{}\mathbf{base}}{\mathbf{weak}\mathbf{}\mathbf{acid}}\right)}$

Calculate the pH of a solution that is 0.242 M C_{6}H_{5}COOH and 0.183 M C_{6}H_{5}COONa. K_{a} of C_{6}H_{5}COOH is 6.5 x 10^{-5}.

a. 2.77

b. 5.81

c. 4.31

d. 4.07

e. 6.19