A student performs a titration to characterize an unknown diprotic acid H₂E
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A student performs a titration to characterize an unknown diprotic acid H₂E. A 60.0 mL sample of the acid solution of unknown concentration is titrated with 0.120 M NaOH at 25 °C. The pH of the solution is recorded at various volumes of base added, producing the following data:
Volume NaOH added (mL) pH
0.00 1.78
15.0 2.58
30.0 3.76
45.0 5.02
60.0 8.65
75.0 10.20
90.0 11.85
Answer the parts below.
(a) Using the data above, determine the volume of NaOH corresponding to each equivalence point. Justify your answer without graphing software.
(b) Calculate the initial molarity of the H₂E solution.
(c) Determine numerical values for Ka1 and Ka2 of the acid. Clearly indicate which data points you use and why they are appropriate for each calculation.
(d) Discuss two potential experimental sources of uncertainty that could affect the accuracy of the acid-dissociation constants obtained.