A 25.00 mL sample of a diprotic acid H₂A of unknown concentration is titrated with…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 25.00 mL sample of a diprotic acid H₂A of unknown concentration is titrated with 0.100 M NaOH at 25 °C. The first sudden rise in pH occurs at a burette reading of 18.20 mL; the second occurs at 36.40 mL. The pH is carefully recorded at two additional key volumes:
• 9.10 mL of NaOH added: pH = 2.90
• 27.30 mL of NaOH added: pH = 7.60
(a) Find the concentration of the original H₂A solution.
(b) Determine pKa1 and Ka1.
(c) Determine pKa2 and Ka2.
(d) Rank H₂A, HA⁻, and A²⁻ in acid strength with justification.
(e) Produce and annotate a qualitative sketch of the titration curve.