A student prepares a buffer solution by dissolving equimolar amounts of acetic acid…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A student prepares a buffer solution by dissolving equimolar amounts of acetic acid (CH₃COOH) and sodium acetate (CH₃COONa) in water. The initial pH of the buffer is measured to be 4.74 at 25 °C.
Answer the following questions qualitatively. No numerical calculations are required.
(a) Describe how the pH of the buffer will change, if at all, when both the acetic acid and the acetate ion concentrations are simultaneously doubled by evaporating half of the solvent while keeping temperature constant.
(b) Explain what happens to the pH when a small amount of strong base that reacts completely with acetic acid is added, assuming the change in total volume is negligible.
(c) Predict and justify the direction of pH change if the temperature is lowered to 15 °C, given that the pKa of acetic acid increases slightly with decreasing temperature.