CHE 5503 -Instrumental Analysis
Midterm II
Prof. Terry A. Ring
Open Book & Open Notes
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Score
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2)__________
3)__________
Total
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1
Problem 1 (30 points)
In the AA analysis of Gatorade, the following data was obtained.
Solution
Blank
Std #1
Std #2
Std #3
Gatorade after HCl
Digestion and Dilution
Concentration (mg K/L)
0±0.02
1.01±0.02
2.00±0.02
2.99±0.02
-
Absorbance (dimensionless)
0±0.001
0.0038±0.0009
0.011±0.001
0.018±0.001
0.013±0.004
This data has the calibration curve given by
A=0.0056 C(mg/L).
a) Determine the concentration of potassium in the Gatorade.
b) Determine the standard deviation of the concentration of potassium in the Gatorade.
2
Problem 2 (40 points)
Attached is a spectrum for natural gas taken with the FTIR spectrometer using the gas
sample cell. In addition the spectra of a sample of 10.1 ppm methane and 10.0 ppm CO2
in the same sample cell has been obtained.
Using the 3010 cm-1 peak for methane and the 2360 cm-1 peak for CO2, determine the
concentration ratio of CO2 in the natural gas to methane (CH4) in the natural gas.
Figure 1 FTIR spectrum of Natural gas
3
Wave Number (cm-1)
Figure 2 FTIR spectrum of 10.1 ppm methane
Figure 3 FTIR spectrum of 10.0 ppm CO2
4
5
Problem 3 (30 Points)
The following results were obtained for the Absorbance of an unknown in the UV-Vis
spectrometer (Spectronic 21). You suspect that the 4th trial is faulty. Use Chauvenets
criterion to determine if it and any other values can be eliminated from the mean and
standard deviation of this absorbance data.
Chauvenet’s Criterion
Data
Trial
Absorbance
1
0.019
2
0.017
3
0.020
4
0.029
5
0.018
6
0.021
6
7