A laboratory stores two stock buffer solutions at 25 °C
CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A laboratory stores two stock buffer solutions at 25 °C, both prepared with a weak acid–conjugate base pair in a 1:1 mole ratio.
• Stock X: 1.0 M in each component
• Stock Y: 0.50 M in each component
Before use, 1.00 L of Stock X is diluted with deionized water to a final volume of 5.00 L, while Stock Y is used without further dilution but warmed to 35 °C. The Ka of the weak acid increases by the same percentage at 35 °C as the Kb of its conjugate base.
A student needs a buffer that can neutralize the largest possible amount of added strong base without a large pH change. Which prepared solution should the student select?
(a) The diluted solution from Stock X, because its larger total number of acid moles allows it to absorb more added base.
(b) The diluted solution from Stock X, because its initial pH is closest to the pK_a of the acid.
(c) The warmed solution from Stock Y, because its component concentrations remain higher after all treatments.
(d) Neither solution, because the 10\,°C temperature rise destroys the buffering ability of Stock Y.