A student titrates 25.0 mL of an unknown base with 0.10 M HCl. During the titration the pH is monitored and the collected data is recorded. These data are shown in the table below.
Volume
Added(mL) pH
0.0 11.13
5.0 9.86
10.0 9.44
12.5 9.26
15.0 9.08
20.0 8.66
22.0 8.39
24.0 7.88
25.0 5.28
26.0 2.70
28.0 2.22
30.0 2.00
35.0 1.70
37.5 1.61
40.0 1.52
45.0 1.40
50.0 1.30
a. Use the information provided to draw a titration curve showing the pH as a function of the volume of added HCl. Be certain to label your axes.
b. Identify the equivalence point on your graph and justify your selection of this particular point.
b. Use the data to determine the Kb value for the weak base. Be certain to show the mathematical steps you take to arrive at the answer. Report your final answer to the correct number of significant digits.
c. The student has three indicators that she could use for this experiment. The indicators (with their endpoints) are: Bromophenol Blue (3.0 – 4.6), Methyl Red (4.2 – 6.3), and phenolphthalein (8.3 – 10.0). Which indicator would be appropriate for this titration? Justify your selection.
e. Determine the (i) molarity and the (ii) % ionization of the original weak base solution (before titrating). Report your answers to the correct number of significant digits.
