Che241: Chemical Principles
Lecture 06 - Spectroscopy Summary Questions
01. What is spectroscopy, and how is it used in science?
Spectroscopy is the study of the interaction between electromagnetic radiation and matter. It
is used in science to identify and analyze chemical compounds, determine the composition
of materials, and study the properties of atoms and molecules.
02. What are the different types of spectroscopy, and how do they work?
There are several types of spectroscopy, including UV-visible spectroscopy, infrared
spectroscopy, Raman spectroscopy, fluorescence spectroscopy, mass spectrometry, and
nuclear magnetic resonance (NMR) spectroscopy. Each type of spectroscopy works by
measuring the way that matter interacts with electromagnetic radiation.
03. How does infrared spectroscopy differ from UV-visible spectroscopy?
Infrared spectroscopy measures the way that matter absorbs or transmits infrared radiation,
while UV-visible spectroscopy measures the way that matter absorbs or transmits ultraviolet
or visible light. Infrared spectroscopy is used primarily to study molecular vibrations, while
UV-visible spectroscopy is used to study electronic transitions.
04. What is the Beer-Lambert Law, and how is it used in spectroscopy?
The Beer-Lambert Law relates the absorbance of a substance to its concentration, path
length, and molar absorptivity. It is used in spectroscopy to determine the concentration of a
solute in a solution by measuring the amount of light that is absorbed by the solute.
05. How is Raman spectroscopy used in chemical analysis?
Raman spectroscopy is used in chemical analysis to identify the chemical composition of a
sample, to determine the structure of molecules, and to study the properties of materials. It
works by measuring the way that light scatters off a sample, which provides information
about the molecular vibrations and rotations of the sample.
06. How does fluorescence spectroscopy work, and what are some of its
applications?
Fluorescence spectroscopy measures the way that matter emits light when it is excited by
electromagnetic radiation. It is used in a wide range of applications, including biochemistry,
material science, and environmental monitoring. Fluorescence spectroscopy can be used to
study the dynamics of chemical reactions, to detect the presence of specific molecules in a
sample, and to analyze the properties of materials.
07. What is mass spectrometry, and how is it used in analytical chemistry?
Mass spectrometry is a technique used to identify and quantify the chemical components of
a sample. It works by ionizing the molecules in a sample, separating them based on their
mass-to-charge ratio, and measuring the resulting ion currents. Mass spectrometry is used
in analytical chemistry to analyze the composition of complex mixtures, to identify unknown
compounds, and to study the properties of biological molecules.
08. How can spectroscopy be used to identify unknown compounds?
Spectroscopy can be used to identify unknown compounds by measuring their absorption or
emission spectra and comparing them to known spectra. By comparing the spectral features
of an unknown compound to those of known compounds, scientists can determine its
chemical composition and structure.
09. How does nuclear magnetic resonance (NMR) spectroscopy work, and what
are its applications?
Nuclear magnetic resonance (NMR) spectroscopy is a technique used to study the
properties of atomic nuclei in a magnetic field. It is used to analyze the structure and
composition of molecules, to study the dynamics of chemical reactions, and to investigate
the properties of materials. NMR spectroscopy works by measuring the resonant frequency
of atomic nuclei in a sample and analyzing the resulting spectra.
10. What is the difference between continuous-wave and pulsed ESR
spectroscopy?
Continuous-wave ESR spectroscopy uses a constant frequency of electromagnetic radiation,
while pulsed ESR spectroscopy uses a series of short pulses of electromagnetic radiation.
Continuous-wave ESR spectroscopy is useful for measuring the magnetic properties of
paramagnetic compounds, while pulsed ESR spectroscopy is useful for studying the
dynamics of molecular interactions and reactions.
11. How does time-resolved spectroscopy work, and what can it tell us about
chemical reactions?
Time-resolved spectroscopy is a technique used to study the dynamics of chemical reactions
by measuring the changes in a sample over time. It works by using short pulses of
electromagnetic radiation to excite a sample and then measuring the changes in the
sample's absorption or emission spectra over time. Time-resolved spectroscopy can provide
information about the kinetics, mechanisms, and pathways of chemical reactions.
12. How is Fourier transform infrared spectroscopy (FTIR) used in materials
science?
Fourier transform infrared spectroscopy (FTIR) is used in materials science to analyze the
chemical composition and structure of materials. It works by measuring the absorption or
transmission of infrared radiation by a sample and using Fourier transform algorithms to
convert the data into a spectral representation. FTIR can be used to analyze a wide range of
materials, including polymers, ceramics, and metals.
13. What is surface-enhanced Raman spectroscopy (SERS), and how does it
enhance sensitivity?
Surface-enhanced Raman spectroscopy (SERS) is a technique used to enhance the
sensitivity of Raman spectroscopy by using nanostructured surfaces to amplify the Raman
signal. SERS works by using a metal substrate to enhance the Raman scattering of a
sample, which can improve the sensitivity of Raman spectroscopy by several orders of
magnitude.
14. How can Raman spectroscopy be used to analyze biological samples?
Raman spectroscopy can be used to analyze biological samples by measuring the Raman
spectra of molecules in the sample. Raman spectroscopy is non-destructive and can provide
information about the chemical composition and structure of biological molecules, including
proteins, DNA, and lipids. Raman spectroscopy can be used for a wide range of applications
in biology, including disease diagnosis, drug discovery, and biophysics.
15. What are some of the challenges associated with interpreting spectroscopic
data, and how can they be addressed?
Interpreting spectroscopic data can be challenging due to the complexity of the spectra and
the large number of possible molecular structures that could produce a given spectrum. To
address these challenges, scientists use a variety of analytical techniques, including
computational modeling, chemometric analysis, and spectral libraries. These techniques can
help to identify the molecular structures that are consistent with the experimental spectra
and to eliminate unlikely candidates.
Multiple Questions
01. What is spectroscopy?
a) The study of colors
b) The study of methods of producing and analyzing spectra
c) The study of living organisms
d) The study of sound waves
Answer: b) The study of methods of producing and analyzing spectra.
Explanation: Spectroscopy is the study of methods of producing and analyzing spectra,
which is a range of electromagnetic energies arranged in order of increasing or decreasing
wavelength or frequency.
02. What is a spectrum?
a) A range of electromagnetic energies
b) A range of colors
c) A range of sound waves
d) A range of living organisms
Answer: a) A range of electromagnetic energies.
Explanation: A spectrum is a range of electromagnetic energies arranged in order of
increasing or decreasing wavelength or frequency.
03. What is atomic spectroscopy?
a) The study of the electromagnetic radiation absorbed or emitted by atoms
b) The study of sound waves produced by atoms
c) The study of colors produced by atoms
d) The study of living organisms
Answer: a) The study of the electromagnetic radiation absorbed or emitted by atoms.
Explanation: Atomic spectroscopy is the study of the electromagnetic radiation absorbed or
emitted by atoms.
04. Which of the following is not a widely accepted analytical method in atomic
spectroscopy?
a) Atomic absorption spectroscopy
b) Atomic emission spectroscopy
c) Mass spectrometry
d) Infrared spectroscopy
Answer: d) Infrared spectroscopy.
Explanation: Infrared spectroscopy is not a widely accepted analytical method in atomic
spectroscopy.
05. What is atomic absorption spectroscopy (AAS)?
a) An analytical technique that measures the concentrations of elements using Atomic
Absorption Spectrometer
b) A technique that measures the color of elements using Atomic Absorption Spectrometer
c) An analytical technique that measures the sound waves produced by elements using
Atomic Absorption Spectrometer
d) An analytical technique that measures the weight of elements using Atomic Absorption
Spectrometer
Answer: a) An analytical technique that measures the concentrations of elements using
Atomic Absorption Spectrometer.
Explanation: Atomic absorption spectroscopy (AAS) is an analytical technique that measures
the concentrations of elements using Atomic Absorption Spectrometer.
06. Which of the following is a principle equipment in a flame AA system?
a) Primary light source
b) Monochromator
c) Detector
d) Atom source
Answer: d) Atom source.
Explanation: The atom source is a principle equipment in flame AA system.
07. How does atomic absorption occur?
a) When a ground state atom emits energy in the form of light of a specific wavelength and is
elevated to an excited state
b) When a ground state atom absorbs energy in the form of light of a specific wavelength
and is elevated to an excited state
c) When a ground state atom emits sound waves and is elevated to an excited state
d) When a ground state atom absorbs sound waves and is elevated to an excited state
Answer: b) When a ground state atom absorbs energy in the form of light of a specific
wavelength and is elevated to an excited state.
Explanation: Atomic absorption occurs when a ground state atom absorbs energy in the form
of light of a specific wavelength and is elevated to an excited state.
08. What is Graphite Furnace Atomic Absorption Spectroscopy (GFAAS)?
a) A technique that measures the concentrations of elements using a graphite tube
b) A technique that measures the color of elements using a graphite tube
c) A technique that measures the sound waves produced by elements using a graphite tube
d) A technique that measures the weight of elements using a graphite tube
Answer: a) A technique that measures the concentrations of elements using a graphite tube.
Explanation: Graphite Furnace Atomic Absorption
Lecture 07 - Ideal Gases Summary Question
Problem 1:
What is the volume of 0.75 moles of oxygen gas at a pressure of 2.5 atm and a
temperature of 25°C?
Solution:
Convert temperature to Kelvin:
25°C + 273.15 = 298.15 K
Use PV = nRT to solve for volume:
V = nRT/P = (0.75 mol)(0.08206 L.atm/mol.K)(298.15 K)/(2.5 atm) = 22.24 L
Answer: The volume of 0.75 moles of oxygen gas at a pressure of 2.5 atm and a
temperature of 25°C is 22.24 L.
Problem 2:
How many moles of nitrogen gas are in a 3.0 L container at a pressure of 1.2 atm and
a temperature of 20°C?
Solution:
Convert temperature to Kelvin:
20°C + 273.15 = 293.15 K
Use PV = nRT to solve for moles:
n = PV/RT = (1.2 atm)(3.0 L)/(0.08206 L.atm/mol.K)(293.15 K) = 0.1445 mol
Answer: There are 0.1445 moles of nitrogen gas in a 3.0 L container at a pressure of 1.2
atm and a temperature of 20°C.
Problem 3:
A 0.50 mol sample of hydrogen gas is in a 2.0 L container at a temperature of 27°C.
What is the pressure of the gas?
Solution:
Convert temperature to Kelvin:
27°C + 273.15 = 300.15 K
Use PV = nRT to solve for pressure:
P = nRT/V = (0.50 mol)(0.08206 L.atm/mol.K)(300.15 K)/(2.0 L) = 6.157 atm
Answer: The pressure of the hydrogen gas is 6.157 atm.
Problem 4:
What is the temperature of a 1.5 mol sample of carbon dioxide gas in a 5.0 L container
at a pressure of 2.0 atm?
Solution:
Use PV = nRT to solve for temperature:
T = PV/nR = (2.0 atm)(5.0 L)/(1.5 mol)(0.08206 L.atm/mol.K) = 218.4 K
Convert temperature to Celsius:
218.4 K - 273.15 = -54.75°C
Answer: The temperature of the carbon dioxide gas is -54.75°C.
Problem 5:
A 4.0 L container is filled with 2.5 moles of neon gas at a pressure of 1.0 atm and a
temperature of 15°C. What is the volume of the gas at a pressure of 2.0 atm and a
temperature of 25°C?
Solution:
Convert temperature to Kelvin:
15°C + 273.15 = 288.15 K
25°C + 273.15 = 298.15 K
Use PV = nRT to solve for volume:
V = nRT/P = (2.5 mol)(0.08206 L.atm/mol.K)(298.15 K)/(1.0 atm) = 60.98 L
Use Boyle's Law to solve for the new volume:
V2 = V1P1/P2 = (4.0 L)(1.0 atm)/(2.0 atm) = 2.0 L
Problem 6:
A 2.50 L container is filled with nitrogen gas at a pressure of 1.25 atm and a
temperature of 25.0°C. What is the number of moles of nitrogen gas present?
Solution:
Convert the temperature to Kelvin: T = 25.0°C + 273.15 = 298.15 K
Rearrange PV = nRT to solve for n: n = PV/RT
Substitute the values: n = (1.25 atm) (2.50 L) / (0.08206 L atm/mol K) (298.15 K) = 0.125 mol
Answer: The number of moles of nitrogen gas present is 0.125 mol.
Problem 7:
A sample of gas occupies a volume of 3.50 L at a pressure of 2.00 atm and a
temperature of 20.0°C. What will be the new pressure if the temperature is raised to
30.0°C and the volume is kept constant?
Solution:
Convert the temperatures to Kelvin: T1 = 20.0°C + 273.15 = 293.15 K, T2 = 30.0°C + 273.15
= 303.15 K
Use the combined gas law: P1/T1 = P2/T2
Solve for P2: P2 = P1 (T2/T1) = 2.00 atm (303.15 K/293.15 K) = 2.06 atm
Answer: The new pressure will be 2.06 atm.
Problem 8:
What volume will 0.20 moles of methane gas occupy at a temperature of 25.0°C and a
pressure of 1.50 atm?
Solution:
Convert the temperature to Kelvin: T = 25.0°C + 273.15 = 298.15 K
Rearrange PV = nRT to solve for V: V = nRT/P
Substitute the values: V = (0.20 mol) (0.08206 L atm/mol K) (298.15 K) / 1.50 atm = 2.03 L
Answer: 0.20 moles of methane gas will occupy a volume of 2.03 L at a temperature of
25.0°C and a pressure of 1.50 atm.