A laboratory technician needs 250.0 mL of an acetate buffer that is 0.200 M in total…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A laboratory technician needs 250.0 mL of an acetate buffer that is 0.200 M in total buffer components (i.e., [CH3COOH]+[CH3COO−]=0.200M) and has a pH of 5.00 at 25 °C. Stock solutions of 1.00 M acetic acid and 1.00 M sodium acetate are available.
(a) Calculate the numerical ratio [CH3COOH][CH3COO−] required to achieve the target pH. (The literature value of pKa for acetic acid at 25 °C is 4.76.)
(b) Determine the number of moles of CH3COO− and CH3COOH that must be present in the final 250.0 mL of buffer.
(c) Calculate the volume of each 1.00 M stock solution that must be combined and then diluted to exactly 250.0 mL to prepare the desired buffer. Assume volume additivity.
(d) If the technician accidentally uses the calculated volume of sodium acetate but only half of the required volume of acetic acid, estimate qualitatively (no calculation necessary) whether the resulting pH will be higher, lower, or unchanged relative to the target pH. Justify your prediction.