Buffer A is prepared by dissolving lactic acid ( , ) and sodium lactate in water to…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Buffer A is prepared by dissolving lactic acid (HC3H5O3, pKa=3.86) and sodium lactate in water to make 200 mL of solution that is 0.30 M in each component. Buffer B is prepared identically, but after preparation, 200 mL of distilled water is added, doubling the volume.
A 1.00 M solution of NaOH is available to adjust the pH of each buffer.
(a) Calculate the initial pH of Buffer A and of Buffer B.
(b) Compute the volume (in mL) of 1.00 M NaOH that must be added to Buffer A to raise its pH by 0.30 unit.
(c) Compute the corresponding volume of 1.00 M NaOH required for Buffer B to achieve the same 0.30-unit pH increase.
(d) Determine the ratio VB/VA and provide a chemical explanation for the difference in the two volumes.