Consider a 250.0 mL solution of 0.20 M propanoic acid. Calculate the mass of sodium propanoate needed to produce a buffer with a pH of 5.11 assuming the volume does not change.

Determine the pH of a 0.500 L solution of 0.15 M lactic acid-0.25 M sodium lactate buffer before and after 0.0050 mol NaOH is added. Assume the volume of NaOH is negligible.

The pK_a of lactic acid is 3.86.