The acid-dissociation constant of acetic acid varies with temperature: pKa = 4.76 at…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
The acid-dissociation constant of acetic acid varies with temperature: pKa = 4.76 at 25 °C and pKa = 4.68 at 37 °C. A 50.0 mL sample of 0.200 M acetic acid is titrated with 0.100 M NaOH.
(a) Calculate the pH of the solution after 30.0 mL of NaOH have been added at 25 °C. Show all work, including stoichiometric and equilibrium steps.
(b) Calculate the pH of an identical titration mixture (same volumes and concentrations) at 37 °C.
(c) Determine the numerical difference between the two pH values obtained in parts (a) and (b) and explain, in terms of acid–base equilibria, why increasing the temperature produces the observed change.
(d) Discuss qualitatively how the temperature-induced change in pKa would influence the buffer capacity of the acetic acid/acetate system near the volume of NaOH used in parts (a) and (b).