What is the pH of the solution?

Question

You have 1.00 liter of a buffer solution where the concentration of lactic acid (HC₃H₅O₃) is 0.200 M and the concentration of sodium lactate (NaC₃H₅O₃) is 0.160 M. The pK_a for lactic acid is 3.85. What is the pH of the solution?

4.65

3.85

3.75

3.95

3.05

Answer 1

Use the Henderson Hasselbalch equation:

pH = pKa + log [salt] /[acid]

pH = ?

pKa = 3.85

[salt] = 0.160 M

[acid] = 0.200 M

pH = 3.85 + log (0.160 / 0.200)

pH = 3.85 + log 0.800

pH = 3.85 + (-0.0969)

pH = 3.75