Intro to Spectroscopy (UV-Vis, IR) - Higher Difficulty Problems
Q. In UV-Vis spectroscopy, what does a higher absorbance indicate about the concentration of a solution?
A.Lower concentration
B.Higher concentration
C.No correlation
D.Increased temperature
Solution
According to the Beer-Lambert Law, higher absorbance indicates a higher concentration of the absorbing species in the solution.
Correct Answer: B — Higher concentration
Q. In UV-Vis spectroscopy, what is the effect of increasing the path length of the sample cell?
A.Decreases absorbance
B.Increases absorbance
C.No effect on absorbance
D.Increases transmittance
Solution
Increasing the path length of the sample cell increases the absorbance according to the Beer-Lambert Law, as absorbance is directly proportional to path length.
Correct Answer: B — Increases absorbance
Q. What is the primary interaction that occurs in UV-Vis spectroscopy?
A.Vibrational transitions
B.Rotational transitions
C.Electronic transitions
D.Nuclear transitions
Solution
UV-Vis spectroscopy primarily involves electronic transitions, where electrons are excited from a lower energy level to a higher energy level.
Correct Answer: C — Electronic transitions
Q. What is the significance of the peak position in an IR spectrum?
A.It indicates the concentration of the sample
B.It reveals the molecular weight of the compound
C.It provides information about the types of bonds present
D.It determines the solubility of the compound
Solution
The peak position in an IR spectrum provides information about the types of bonds present in the molecule, as different bonds absorb at characteristic frequencies.
Correct Answer: C — It provides information about the types of bonds present
Q. What type of bond is primarily detected in the fingerprint region of an IR spectrum?
A.C-H bonds
B.O-H bonds
C.C-C bonds
D.Complex vibrations of multiple bonds
Solution
The fingerprint region of an IR spectrum (typically 400-1500 cm-1) is characterized by complex vibrations of multiple bonds, making it unique for different compounds.
Correct Answer: D — Complex vibrations of multiple bonds
Q. Which instrument is commonly used to measure the absorbance of a sample in UV-Vis spectroscopy?
A.Mass spectrometer
B.Chromatograph
C.Spectrophotometer
D.Fluorometer
Solution
A spectrophotometer is the instrument used to measure the absorbance of a sample in UV-Vis spectroscopy.
