A student titrates 25.00 mL of an aqueous solution of a monoprotic weak acid HA with 0.150 M NaOH. The student collects the following data. (All volumes are cumulative volumes of NaOH delivered.)
Volume NaOH added (mL) → 0.00 5.00 9.00 12.00 16.00 17.50 18.25 20.00
Measured pH → 3.25 4.00 4.58 4.83 4.95 6.80 9.05 11.10
(a) Using the table, identify the volume of NaOH that most closely corresponds to the stoichiometric equivalence point. Explain your reasoning based on the trend in pH.
(b) Calculate the initial molarity of the acid solution.
(c) Determine the numerical value of Ka for the acid. Show all steps leading to your answer.
(d) Published data list Ka=1.8×10−5 for ethanoic acid. Calculate the percent error of the experimentally determined Ka relative to this reference value.
(e) The pH measurements have an uncertainty of ±0.02 pH units. Qualitatively discuss how this uncertainty affects the precision of the calculated Ka.
(a) Identify the equivalence volume and justify the choice.
(b) Calculate the initial molarity of the acid.
(c) Calculate Ka for the acid.
(d) Compute the percent error relative to the published value.
(e) Discuss the impact of ±0.02 pH uncertainty on the calculated Ka. No calculations are required.