The Intro to Spectroscopy (UV–Vis, IR) – Case Studies section applies spectroscopic principles to real laboratory, industrial, environmental, and forensic scenarios, helping students develop interpretation, reasoning, and problem-solving skills. This module is designed for Class 11–12 students and undergraduate learners, with emphasis on case-based questions increasingly asked in exams and practical assessments.
In this section, you will work through:
UV–Vis case studies – concentration determination errors, Beer–Lambert law deviations, and solvent effects
IR spectroscopy case studies – functional group identification from unknown spectra
Structural analysis cases – distinguishing similar compounds using UV–Vis and IR data
Quality control scenarios – impurity detection in pharmaceuticals and industrial samples
Environmental and forensic cases – identification of pollutants and unknown substances
Instrumentation-related cases – baseline drift, noise, and resolution issues
Comparative case analysis – UV–Vis vs IR applicability for different analytical problems
NCERT- and UG-aligned case discussions, supported by spectra interpretation exercises, data tables, MCQs, and viva-oriented explanations
The content is structured to strengthen analytical reasoning, improve spectral interpretation skills, and prepare students for case-based questions in exams, practicals, and viva voce.
Develop a problem-solving mindset in UV–Vis and IR spectroscopy by analyzing realistic case studies that reflect true analytical challenges.
Q. In a UV-Vis spectrum, what does a higher absorbance value indicate?
A.
Lower concentration of the analyte
B.
Higher concentration of the analyte
C.
Presence of impurities
D.
Increased solvent interference
Solution
A higher absorbance value in a UV-Vis spectrum indicates a higher concentration of the analyte, according to Beer-Lambert law.
Correct Answer:
B
— Higher concentration of the analyte
Q. In IR spectroscopy, what does a peak at around 1700 cm-1 typically indicate?
A.
Presence of alcohols
B.
Presence of carbonyl groups
C.
Presence of amines
D.
Presence of alkenes
Solution
A peak at around 1700 cm-1 in IR spectroscopy typically indicates the presence of carbonyl (C=O) groups, which are characteristic of ketones and aldehydes.
Q. In the context of IR spectroscopy, what does the term 'fingerprint region' refer to?
A.
The region above 4000 cm-1
B.
The region between 400-1500 cm-1
C.
The region below 400 cm-1
D.
The region between 1500-2000 cm-1
Solution
The 'fingerprint region' in IR spectroscopy refers to the region between 400-1500 cm-1, where many unique absorption bands occur for different compounds.
Correct Answer:
B
— The region between 400-1500 cm-1
Q. What does the term 'Beer-Lambert Law' describe?
A.
The relationship between temperature and absorbance
B.
The relationship between concentration and absorbance
C.
The relationship between wavelength and absorbance
D.
The relationship between time and absorbance
Solution
The Beer-Lambert Law describes the linear relationship between the concentration of a solute in a solution and the absorbance of light at a specific wavelength.
Correct Answer:
B
— The relationship between concentration and absorbance
Q. What is the main advantage of using a diode array detector in UV-Vis spectroscopy?
A.
Higher resolution
B.
Simultaneous detection of multiple wavelengths
C.
Lower cost
D.
Simpler sample preparation
Solution
A diode array detector allows for the simultaneous detection of multiple wavelengths, enabling rapid data collection and analysis in UV-Vis spectroscopy.
Correct Answer:
B
— Simultaneous detection of multiple wavelengths
Q. What is the primary purpose of UV-Vis spectroscopy?
A.
To measure the mass of a sample
B.
To determine the concentration of a substance
C.
To separate components of a mixture
D.
To identify the molecular structure
Solution
UV-Vis spectroscopy is primarily used to determine the concentration of a substance in a solution based on the absorbance of light at specific wavelengths.
Correct Answer:
B
— To determine the concentration of a substance
Q. What is the significance of the baseline in an IR spectrum?
A.
It indicates the presence of noise
B.
It represents the absorbance of the solvent
C.
It shows the sample concentration
D.
It is used for calibration purposes
Solution
The baseline in an IR spectrum represents the absorbance of the solvent and any background noise, which is important for accurate interpretation of the sample peaks.
Correct Answer:
B
— It represents the absorbance of the solvent
Q. Which of the following compounds would you expect to show strong absorption in the UV region?
A.
Alkanes
B.
Aromatic compounds
C.
Alcohols
D.
Carboxylic acids
Solution
Aromatic compounds have delocalized π electrons that can absorb UV light, leading to strong absorption in the UV region, unlike alkanes which do not absorb UV light.
Q. Which of the following is NOT a common use of IR spectroscopy?
A.
Identifying functional groups
B.
Determining molecular weight
C.
Analyzing chemical bonds
D.
Studying molecular vibrations
Solution
Determining molecular weight is not a common use of IR spectroscopy; it is primarily used for identifying functional groups and analyzing molecular vibrations.
