Intro to Spectroscopy (UV-Vis, IR)
Q. In IR spectroscopy, which region is typically used to identify functional groups?
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A.
Near-infrared region
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B.
Mid-infrared region
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C.
Far-infrared region
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D.
Ultraviolet region
Solution
The mid-infrared region is typically used to identify functional groups due to the characteristic absorption bands.
Correct Answer: B — Mid-infrared region
Q. In IR spectroscopy, which type of molecular vibration is primarily detected?
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A.
Rotational transitions
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B.
Translational movements
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C.
Vibrational modes
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D.
Electronic transitions
Solution
IR spectroscopy detects vibrational modes of molecules, which occur when bonds stretch or bend.
Correct Answer: C — Vibrational modes
Q. What does the term 'chromophore' refer to in UV-Vis spectroscopy?
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A.
A molecule that fluoresces
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B.
A part of a molecule responsible for its color
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C.
A solvent used in the analysis
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D.
A detector used in the instrument
Solution
A chromophore is the part of a molecule that is responsible for its color and absorbs light in the UV-Vis region.
Correct Answer: B — A part of a molecule responsible for its color
Q. What is the Beer-Lambert Law used for in UV-Vis spectroscopy?
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A.
To calculate the wavelength of light
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B.
To determine the concentration of a solution
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C.
To measure the intensity of emitted light
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D.
To analyze the molecular structure
Solution
The Beer-Lambert Law relates the absorbance of light to the concentration of a solution, allowing for concentration determination.
Correct Answer: B — To determine the concentration of a solution
Q. What is the main advantage of using UV-Vis spectroscopy over other analytical techniques?
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A.
It requires no sample preparation
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B.
It can analyze solid samples directly
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C.
It provides rapid and quantitative analysis
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D.
It is less expensive than other methods
Solution
UV-Vis spectroscopy provides rapid and quantitative analysis, making it a preferred method for many applications.
Correct Answer: C — It provides rapid and quantitative analysis
Q. What is the 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 concentration
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C.
To account for solvent absorbance
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D.
To enhance signal detection
Solution
A blank is used to account for the absorbance of the solvent, ensuring that only the sample's absorbance is measured.
Correct Answer: C — To account for solvent absorbance
Q. What type of sample preparation is often required for solid samples in IR spectroscopy?
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A.
Dissolving in water
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B.
KBr pellet formation
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C.
Dilution in ethanol
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D.
Heating to vaporize
Solution
Solid samples in IR spectroscopy are often prepared by forming KBr pellets to allow for proper transmission of IR light.
Correct Answer: B — KBr pellet formation
Q. Which of the following instruments is commonly used for IR spectroscopy?
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A.
Mass spectrometer
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B.
Nuclear magnetic resonance spectrometer
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C.
Fourier-transform infrared spectrometer
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D.
Gas chromatograph
Solution
A Fourier-transform infrared spectrometer (FTIR) is commonly used for IR spectroscopy to obtain high-resolution spectra.
Correct Answer: C — Fourier-transform infrared spectrometer
Q. Which of the following is a common application of UV-Vis spectroscopy?
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A.
Determining molecular weight
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B.
Analyzing protein structure
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C.
Measuring pH levels
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D.
Quantifying concentrations of colored solutions
Solution
UV-Vis spectroscopy is commonly used to quantify concentrations of colored solutions based on their absorbance.
Correct Answer: D — Quantifying concentrations of colored solutions
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