Intro to Spectroscopy (UV-Vis, IR) - Numerical Applications
Q. If a compound has a molar absorptivity of 200 L/(mol·cm) and a concentration of 0.01 mol/L, what is the absorbance at a path length of 1 cm?
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A.
0.2
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B.
2
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C.
20
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D.
0.02
Solution
Using Beer-Lambert Law (A = εlc), A = 200 L/(mol·cm) * 0.01 mol/L * 1 cm = 2.
Correct Answer: A — 0.2
Q. In a UV-Vis spectrum, what does a peak at 260 nm typically indicate?
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A.
Proteins
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B.
Nucleic acids
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C.
Lipids
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D.
Carbohydrates
Solution
A peak at 260 nm is characteristic of nucleic acids, particularly DNA and RNA.
Correct Answer: B — Nucleic acids
Q. In IR spectroscopy, which functional group is characterized by a strong absorption around 1700 cm-1?
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A.
Alcohols
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B.
Aldehydes
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C.
Carboxylic acids
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D.
Ketones
Solution
Ketones typically show a strong carbonyl (C=O) absorption around 1700 cm-1 in IR spectroscopy.
Correct Answer: D — Ketones
Q. In UV-Vis spectroscopy, what does a higher absorbance indicate about the concentration of a sample?
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A.
Lower concentration
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B.
Higher concentration
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C.
No correlation
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D.
Increased path length
Solution
According to Beer-Lambert Law, higher absorbance indicates a higher concentration of the absorbing species.
Correct Answer: B — Higher concentration
Q. What is the effect of increasing the path length in a UV-Vis spectrophotometer?
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A.
Decreases absorbance
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B.
Increases absorbance
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C.
No effect on absorbance
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D.
Increases wavelength
Solution
Increasing the path length increases the absorbance according to Beer-Lambert Law.
Correct Answer: B — Increases absorbance
Q. What is the primary purpose of using a blank in UV-Vis spectroscopy?
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A.
To calibrate the instrument
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B.
To measure the sample absorbance
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C.
To account for solvent effects
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D.
To determine the concentration
Solution
A blank is used to account for any absorbance due to the solvent or other components in the sample.
Correct Answer: C — To account for solvent effects
Q. What is the typical range of wavelengths for infrared (IR) spectroscopy?
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A.
400-700 nm
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B.
700-1400 nm
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C.
1400-4000 nm
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D.
4000-10000 nm
Solution
Infrared spectroscopy typically operates in the range of 1400 to 4000 nm.
Correct Answer: C — 1400-4000 nm
Q. What is the wavelength range of UV-Vis spectroscopy?
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A.
100-400 nm
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B.
400-700 nm
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C.
700-1000 nm
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D.
1000-2000 nm
Solution
UV-Vis spectroscopy typically covers the wavelength range from 100 to 400 nm for UV and 400 to 700 nm for visible light.
Correct Answer: A — 100-400 nm
Q. Which of the following is NOT a common application of UV-Vis spectroscopy?
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A.
Determining protein concentration
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B.
Measuring pH
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C.
Analyzing colored compounds
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D.
Monitoring reaction kinetics
Solution
UV-Vis spectroscopy is not typically used for direct pH measurement.
Correct Answer: B — Measuring pH
Q. Which type of spectroscopy is best suited for identifying functional groups in organic compounds?
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A.
NMR
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B.
UV-Vis
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C.
IR
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D.
Mass Spectrometry
Solution
Infrared (IR) spectroscopy is best suited for identifying functional groups due to its ability to measure molecular vibrations.
Correct Answer: C — IR
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