Chemistry 420
Problem set #3 (80 points total)
—Key
Due at the beginning of class October 29
No late assignments will be accepted.
Assignments are due at beginning of class—starts at 12 Noon!
For full credit assignments must be in box when the lecture begins.
Any assignment turned in between noon and 12:05 PM will automatically be deducted 5 points.
Assignments will NOT be accepted for credit after 12:05 PM. Score = 0
No name, no grade.
Show all of your work for each answer. Partial credit will be given and NO credit will be awarded if no work is
shown. Be careful to use correct significant figures.
1.
(12 points, Skoog 26
‐
14) The following data are for a liquid chromatographic column
Length of packing
24.7 cm
Flow rate
0.313 mL/min
V
M
1.37 mL
V
S
0.164 mL
A chromatogram of a mixture of species A, B, C, and D provided the following data:
Retention time,
minutes
Width of Peak Base (
W
),
minutes
Nonretained
3.1
—
A
5.4
0.41
B
13.3
1.07
C
14.1
1.16
D
21.6
1.72
Calculate:
a)
the number of plates from each peak.
b)
the mean and the standard deviation for N.
c)
the plate height for the column.
(a) 2 points for setup, 1 point for each answer,
‐
0.5 for sig figs
2
2
2
3
3
2
3
16
5.4
13.3
for A:
16
2775 or 2.8x10
or 2800 plates
for B:
16
2472 or 2.47x10
or 2470 plates
0.41
1.07
14.1
for C:
16
2365 or 2.36x10
or 2360 plates
fo
1.16
R
t
N
W
N
N
N
⎛
⎞
=
⎜
⎟
⎝
⎠
⎛
⎞
⎛
⎞
=
=
=
=
⎜
⎟
⎜
⎟
⎝
⎠
⎝
⎠
⎛
⎞
=
=
⎜
⎟
⎝
⎠
2
3
21.6
r D:
16
2523 or 2.52x10
or 2520 plates
1.72
N
⎛
⎞
=
=
⎜
⎟
⎝
⎠
(b) 1 point for each setup, 1 point for each answer,
‐
0.5 for sig figs
(
)
(
)
(
)
(
)
3
2
2
2
2
2
2775
2472
2365
2523
2534 or 2.53x10
plates
4
2775- 2534
2472- 2534
2365- 2534
2523- 2534
174 or 2x10
4-1
N
SD
+
+
+
=
=
+
+
+
=
=

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