CHEMISTRY
133
Spring,
2017 Homework Set 3
Only Additional
Problems are Submitted for Grading
Set 3.1 -
Complete for quiz on May 4th
Ch. 22: 2,
7a, 17, 19, 22, 24, 26, 28, 31, 32, 38, 42, 43
Homework Solutions to Set3.1 Text Problems
Additional Problem 3.1 The table below shows the
retention times and peak widths for 3 compounds separated by reversed-phase
HPLC using a 250 mm length x 4.6 mm inside diameter column with an eluent of
45% acetonitrile, 55% water:
|
Compound |
Retention
time (min.) |
Peak
Width at half height (min.) |
pKa |
|
phenol |
4.72 |
0.21 |
9.98 |
|
2-nitrophenol |
5.68 |
0.25 |
8.39 |
|
2-methylphenol |
5.91 |
0.26 |
10.09 |
Note: wb = 1.70*w1/2
a) If the flow rate is 1.00 mL/min and the
column is 62% by volume packing material (including stationary phase),
calculate the time it takes for mobile phase to flow through the column.
b) Calculate the retention factor for phenol.
c) Calculate the plate number for the column using the last
eluting compound.
d) Calculate the resolution for the two least well-resolved
peaks.
e) Calculate the relative retention (a) for the two least well-resolved peaks.
f) If the solvent is changed to an eluent of 45%
acetonitrile, 55% pH = 8 buffer (about the maximum
possible), what will happen to each retention time. You can assume that anions are unretained
Additional Problem 3.2. A gas bubble meter is used to determine the flow rate for a 0.32 mm (open tubular), 30 m column. If the column effluent takes 136 s for a bubble to travel 10.0 mL in the meter, calculate:
a) the flow rate at the bubble meter (mL/min)
b) the linear velocity (m/s)
c) the time expected for unretained solute to elute
For this question, you can ignore changes in temperature and pressure as the gas flows through the column (as well as any fraction of the bubble meter made up of water vapor).
Set 3.2 – Complete by May 11th
Ch. 23: 3a, 5, 17,
Ch. 24 1a, 4, 15