Electromagnetic Radiation and Spectrum
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Questions and Answers

Which of the following describes electromagnetic radiation?

  • A form of thermal energy
  • A type of sound wave
  • A stream of massive particles
  • A stream of mass-less particles called photons (correct)

    • Electromagnetic radiation propagates in the direction of the electric field.

    False

    What is the unit of frequency?

    Hertz (Hz)

    The formula for energy associated with electromagnetic radiation is E = h υ, where h is __________.

    <p>Planck's constant</p> Signup and view all the answers

    What does the wave number represent?

    <p>The number of waves per unit distance</p> Signup and view all the answers

    Match the types of energy levels with their descriptions:

    <p>Electronic Energy Levels = Molecules in the lowest energy state at room temperature Vibrational Energy Levels = Lower energy than electronic energy levels</p> Signup and view all the answers

    Spectroscopy involves the measurement of electromagnetic radiation alone.

    <p>False</p> Signup and view all the answers

    What is the electromagnetic spectrum?

    <p>The arrangement of electromagnetic radiations in order of wavelength and frequency.</p> Signup and view all the answers

    What does Beer’s law express about the intensity of light?

    <p>Intensity decreases exponentially as concentration increases.</p> Signup and view all the answers

    Beer-Lambert law can apply to solutions with scattered light.

    <p>False</p> Signup and view all the answers

    What is the formula representing the relationship between light intensity and thickness of the medium according to Beer’s law?

    <p>I = I₀ e^(-kc l)</p> Signup and view all the answers

    According to Beer-Lambert law, the molar absorption coefficient is represented by the symbol ______.

    <p>ε</p> Signup and view all the answers

    Match the terms related to Beer-Lambert law with their definitions:

    <p>I = Intensity of the transmitted light I₀ = Intensity of the incident light c = Concentration of the absorbing substance l = Thickness of the medium</p> Signup and view all the answers

    Which of the following conditions must be met for Beer-Lambert law to be applicable?

    <p>The electromagnetic radiation should be monochromatic.</p> Signup and view all the answers

    The Beer-Lambert law can be expressed using the formula A = log10 I₀ = εcl.

    <p>True</p> Signup and view all the answers

    What does the variable 'k' represent in the equation I = I₀ e^(-kc l) used in Beer’s law?

    <p>The proportionality constant related to absorption.</p> Signup and view all the answers

    Which transition is typically found in compounds with conjugated double bonds?

    <p>π – π* transition</p> Signup and view all the answers

    The Beer-Lambert law can only be used for qualitative analysis.

    <p>False</p> Signup and view all the answers

    What wavelength range corresponds to the visible region in the electromagnetic spectrum?

    <p>400-700 nm</p> Signup and view all the answers

    In the Beer-Lambert law, absorbance is directly related to the ______ of the material.

    <p>concentration</p> Signup and view all the answers

    Match the transitions with their corresponding wavelength ranges:

    <p>σ – σ* transition = 100 to 135 nm π – π* transition (conjugated) = 210 to 280 nm n - π* transition = 270 to 320 nm π – π* transition (isolated) = 160 to 175 nm</p> Signup and view all the answers

    Which type of compound shows absorption in the range of 270-320 nm?

    <p>Compounds with lone pair electrons and double bonds</p> Signup and view all the answers

    UV rays fall in the wavelength range of 100-400 nm.

    <p>True</p> Signup and view all the answers

    Name one example of a compound that shows a π – π* transition.

    <p>Ethylene (C2H4)</p> Signup and view all the answers

    Which electronic transition involves the excitation of nonbonding electrons to σ* anti-bonding orbitals?

    <p>n-σ* transition</p> Signup and view all the answers

    Singlet-triplet transitions are allowed transitions according to selection rules.

    <p>False</p> Signup and view all the answers

    What is the main purpose of a monochromator in UV spectroscopy?

    <p>To resolve polychromatic light into monochromatic light.</p> Signup and view all the answers

    The light source that covers the UV-visible region from 200 to 400 nm is called the ______.

    <p>Hydrogen-Deuterium lamp</p> Signup and view all the answers

    Match the following components of a UV spectrophotometer with their functions:

    <p>Light Source = Provides electromagnetic radiation Beam Splitter = Divides light into sample and reference beams Detector = Converts light signal to electrical signal Cuvette = Holds the sample solution</p> Signup and view all the answers

    Which material is NOT suitable for cuvettes used in UV spectroscopy?

    <p>Glass</p> Signup and view all the answers

    What is measured after the absorption of energy by the compound in UV spectroscopy?

    <p>The absorption spectrum or absorbance.</p> Signup and view all the answers

    The excitation energy of the n-σ* transition is observed in the near UV region.

    <p>True</p> Signup and view all the answers

    What is the primary function of the stationary phase in chromatography?

    <p>To absorb components from the mobile phase</p> Signup and view all the answers

    The mobile phase is a stationary substance that moves with the sample.

    <p>False</p> Signup and view all the answers

    What is the term for the solvent used for the separation of absorbed material from the stationary phase?

    <p>Eluent</p> Signup and view all the answers

    The time taken for a particular analyte to pass through the system is called __________.

    <p>retention time</p> Signup and view all the answers

    Which of the following statements about High Performance Liquid Chromatography (HPLC) is correct?

    <p>It can utilize liquid stationary phases for partition chromatography.</p> Signup and view all the answers

    In chromatography, an elute is defined as the fluid containing the sample that exits the column.

    <p>True</p> Signup and view all the answers

    Match the following chromatography terms with their correct definitions:

    <p>Solvent = A substance capable of dissolving another Column = Device used for separation of chemical compounds Degasser = Removes dissolved gases from eluent Chromatogram = Plot of signal versus time in chromatography</p> Signup and view all the answers

    The process of removing adsorbed material from the stationary phase is known as __________.

    <p>elution</p> Signup and view all the answers

    What is the primary function of the pump in HPLC?

    <p>To deliver the mobile phase at a constant flow rate</p> Signup and view all the answers

    The detector in HPLC produces a signal that is independent of the concentration of the eluted components.

    <p>False</p> Signup and view all the answers

    What are the typical temperature conditions for some analyses in HPLC, such as sugar and organic acid?

    <p>50 to 80°C</p> Signup and view all the answers

    The __________ is used to introduce the sample into the mobile phase.

    <p>injector</p> Signup and view all the answers

    Which component is responsible for separating analytes inside the column?

    <p>Column</p> Signup and view all the answers

    The composition of the eluent remains consistent only when no analyte is present.

    <p>True</p> Signup and view all the answers

    Match the following HPLC components with their functions:

    <p>Pump = Delivers mobile phase Injector = Introduces sample Column = Contains stationary phase Detector = Monitors eluent</p> Signup and view all the answers

    A __________ records and analyzes the output of the detector and produces a chromatogram.

    <p>data processing unit</p> Signup and view all the answers

    Study Notes

    Electromagnetic Radiation

    • Electromagnetic radiation is a stream of massless particles (photons) that travel in waves at the speed of light.
    • It consists of oscillating electric and magnetic fields that are perpendicular to each other and the direction of propagation.
    • Properties include wavelength (λ), frequency (ν), wave number (υ), and energy (E).
    • Wavelength is the distance between two consecutive crests or troughs.
    • Frequency is the number of waves passing a point per second.
    • Wave number is the reciprocal of wavelength.
    • Energy is related to frequency (E = hν), where h is Planck's constant. It is also related to wavelength (E = hc/λ), with c being the speed of light.

    Electromagnetic Spectrum

    • The electromagnetic spectrum is the arrangement of electromagnetic radiations in order of increasing or decreasing wavelength and frequency.
    • It ranges from cosmic rays to radio waves, with various types in between (gamma rays, X-rays, UV, visible, near IR, far IR, micro, and radio waves).
    • Different types of electromagnetic radiation possess different energies, which determine their interaction with matter.
    • The energy associated with electromagnetic radiation is linked to its frequency. Higher frequency means higher energy.
    • Different types of transitions (electronic, vibrational, rotational) are excited in matter by absorbing different ranges on the electromagnetic spectrum.

    Spectroscopy

    • Spectroscopy is the study of the interaction between electromagnetic radiation and matter.
    • Interactions cause changes in the energy levels of matter, and these transitions can be determined by measuring the absorption, emission or scattering of radiation.
    • Different types of energy levels include electronic energy levels (UV-Visible spectrum), vibrational energy levels (Infrared, IR spectrum), and rotational energy levels (Microwave spectrum).
    • Relationships/differences between translational, rotational, vibrational and electronic energy contributions to the total energy of a molecule, E = Etrans + Erot + Evib + Eelec.

    UV-Visible Spectroscopy

    • Absorption spectroscopy using UV and visible light (100–700 nm)
    • Electrons in molecules absorb UV/visible radiation and transition to higher energy levels (electronic transitions).
    • Different types of electronic transitions exist (e.g., n–π*, π–π*, σ–σ*).
    • Absorption spectra are used to identify and quantify compounds and study structural features (like conjugated systems).

    IR Spectroscopy

    • Absorption spectroscopy using infrared light (IR)
    • Vibrational energy levels in molecules absorb IR radiation causing transitions (vibrational transitions).
    • Distinction between stretching and bending vibrations.
    • Molecular vibrations change the dipole moment of the molecule, determining whether or not that transition is active in IR.
    • Different types of stretching (symmetrical and asymmetrical) and bending vibrations exist (scissoring, rocking, twisting and wagging).
    • IR spectra are used to identify functional groups and structure of molecules.

    Chromatography

    • Chromatography is a technique used to separate components of a mixture, analyze, identify, purify, and quantify components.
    • Separations based on differences in interaction between components and two phases:
      • Stationary phase (solid or liquid) and mobile phase (liquid or gas)
    • Different types of chromatography techniques include:
      • Adsorption, Thin layer, High-performance liquid, Gas-liquid, Partition

    HPLC (High-Performance Liquid Chromatography)

    • HPLC is a liquid chromatography technique providing high resolution and sensitivity for separating and analyzing components of a mixture through a column.
    • Involves a pump for a constant flow rate of the mobile phase, an injector for sample introduction, a column for separation, and a detector that measures the eluting components.
    • Different types of detectors employed produce a chromatogram used for analyte identification.
    • Understanding the concept of retention time (tR) between peaks in the chromatogram.

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    Description

    This quiz explores the concept of electromagnetic radiation, including its characteristics such as wavelength, frequency, and energy. It also delves into the electromagnetic spectrum, outlining the various types of radiation from cosmic rays to radio waves. Test your understanding of these fundamental topics in physics!

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