Calculate the pH of a buffer solution that is 0.0876 M in benzoic acid (HC7H5O2) and 0.565 M in sodium benzoate (NaC7H5O2). For benzoic acid, Ka=6.54*10^-5.

Question

Calculate the pH of a buffer solution as an equilibrium problem and with the henderson-hasselbalch equation.

Answer 1

Use the Henderson Hasselbalch equation:

pH = pKa + log [NaC7H5O2] / [HC7H5O2]

pKa = -log Ka = -log 6.54x10^-5 = 4.18

pH = 4.18 + log [0.565] / [0.0876]

pH = 4.18 + log 6.45

pH = 4.18 + 0.81

pH = 4.99