A 50.0 mL sample of a diprotic acid H A is titrated with 0.200 M KOH
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 50.0 mL sample of a diprotic acid H2A is titrated with 0.200 M KOH. A first-derivative analysis of the pH–volume curve reveals two sharp peaks at 20.2 mL and 40.5 mL of KOH added. Additional pH measurements give the following information:
• When 10.1 mL of KOH have been added, the pH is 3.09.
• When 30.4 mL of KOH have been added, the pH is 7.55.
Answer the questions below regarding the titration.
(a) Determine the concentration (mol L−1) of the original H2A solution.
(b) Calculate pKa1 and pKa2 for the acid.
(c) Sketch qualitatively how the titration curve would differ if the same titration were performed with 0.100 M KOH instead of 0.200 M KOH, focusing on the positions of the equivalence points and the overall shape.
(d) Estimate the pH that would be observed exactly at the first equivalence point of the original titration (20.2 mL added). Clearly state any assumptions made.