CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
During an investigation, students titrate an unknown monoprotic weak acid with 0.100 M KOH and generate the following verbal description of the pH versus volume curve:
• The curve begins at pH 2.90 with 0 mL of base added.
• A gentle, almost linear rise is observed until approximately 14.0 mL of base have been delivered, at which point the pH is 4.75.
• A steep rise follows, centering at 28.0 mL where the pH passes through 8.80.
• Beyond 32 mL the curve levels off above pH 11.
(a) Estimate the half-equivalence volume from the curve description.
(b) Determine pKa and calculate Ka.
(c) Calculate [A⁻] at the half-equivalence point.
(d) Predict and justify the effect of using 0.050 M KOH on the calculated pKa.