Two separate titrations are carried out at 25 °C using identical burettes that…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Two separate titrations are carried out at 25 °C using identical burettes that deliver 0.100 M NaOH.
• Titration I: 25.0 mL of 0.100 M HCl (strong acid)
• Titration II: 25.0 mL of 0.100 M HF (weak acid, Ka=6.6×10−4)
In each experiment, a large excess of NaOH is added well past the equivalence point.
(1) Without performing numerical calculations, compare qualitatively the pH values 20.0 mL beyond the equivalence point for Titration I and Titration II. Provide chemical reasoning for any difference or similarity you predict.
(2) Explain why, for either titration, progressively larger additions of NaOH after the equivalence point result in increasingly smaller changes in pH.
(3) In Titration II, discuss the relative roles of (i) dilution of the hydroxide ion and (ii) the presence of the conjugate base F⁻ in determining the pH shape in the post-equivalence region.