6-14: Study of Acid-Base Titrations-Polyprotic Acids (Virtual ChemLab) OVERVIEW:
ID: 941314 • Letter: 6
Question
6-14: Study of Acid-Base Titrations-Polyprotic Acids (Virtual ChemLab)
OVERVIEW:
The buret will be filled with NaOH, and 25.00 mL of H2SO3 will be in the beaker with the thymol blue as an indicator. At this point, I opened the stopcock and let the volume reach 40mL.
(the beaker contains 0.2556 M H2SO3 and the buret contains 0.3106 M NaOH.)
QUESTION:
Based on the graph, what happens to the pH around 16 mL and 32mL. What causes each to occur?
To give a little more information, below is the relation between volume, pH, and conductivity values around the volumes of 16 and 32mL
Volume pH Conductivity
14.84 2.81 14.21
15.25 2.95 14.19
15.64 3.15 14.20
16.04 3.44 14.18
16.44 4.33 14.23
16.94 5.30 14.67
17.34 5.56 15.04
...
31.57 7.80 21.74
31.98 7.97 21.82
32.38 8.24 21.89
32.79 8.94 21.96
33.19 11.09 22.17
Plot 50 12F -40 10 30 S -20 -10 10 30 40 50 Volume VCLExplanation / Answer
The 16 ml addition of 0.3106 M NaOH to 25 ml of 0.2556 M H2SO3 leads to the first deprotonation step of H2SO3 which is confirmed by the sudden increase in pH and conductivity. Similarly, addition of 32mL of 0.3106 M NaOH to 0.2556 M H2SO3 leads to the second deprotonation step of H2SO3 which is confirmed by the sudden increase in pH and conductivity.
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