A student is assigned to determine the concentration of a commercial vinegar sample…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A student is assigned to determine the concentration of a commercial vinegar sample by titrating it with standardized 0.100 M NaOH solution. Phenolphthalein is chosen as the indicator. After adding NaOH from a buret, the student swirls continuously and stops the titration when a faint pink color persists for 30 s.
(a) Define the term equivalence point for this titration.
(b) Define the term end point for this titration and describe the macroscopic observation that signals it.
(c) Explain two distinct reasons why the equivalence point and the end point for this titration might not occur at exactly the same volume of added NaOH.
(d) Using acid–base principles, explain the role of phenolphthalein in allowing the student to detect the end point. Your explanation should include reference to the indicator’s acid–base conjugate pair.
(e) If the student stops titrating when the solution is a deep rather than faint pink, predict qualitatively whether the calculated molarity of acetic acid will be higher than, lower than, or equal to the true value. Justify your prediction.