A student titrates 50.0 mL of 0.100 M diprotic acid H₂A (pKa₁ = 2.40
CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A student titrates 50.0 mL of 0.100 M diprotic acid H₂A (pKa₁ = 2.40, pKa₂ = 6.80) with 0.100 M NaOH. Which point on the resulting titration curve corresponds to the second half-equivalence?
(a) The initial pH of the pure H2A solution before any NaOH is added (pH ≈ 1.0).
(b) The midpoint of the first buffer region where 25.0 mL of NaOH has been added and the pH is ≈ 2.4.
(c) The nearly flat region where 75.0 mL of NaOH has been added—halfway between the two equivalence points—and the pH is ≈ 6.8.
(d) The first sharp rise that occurs at 50.0 mL of NaOH added, marking the first equivalence point.