Spectrophotometry Chapter 2
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Questions and Answers

What is the primary function of a monochromator?

  • To filter out specific wavelengths of light
  • To amplify light intensity
  • To convert monochromatic light to polychromatic light
  • To separate polychromatic light into individual wavelengths (correct)

    • Which component of a monochromator creates a parallel beam after the entrance slit?

  • Camera mirror
  • Diffraction grating
  • Collimating mirror (correct)
  • Exit slit

    • Which of the following is NOT one of the basic components of a monochromator?

  • Exit slit
  • Diffraction grating
  • Entrance slit
  • Prism (correct)

    • What is the role of the diffraction grating in a monochromator?

    <p>To disperse light into its individual wavelengths</p> Signup and view all the answers

    How many main types of monochromators are there?

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

    What is the function of a cuvette in the given setup?

    <p>Hold liquid analyte</p> Signup and view all the answers

    Which type of lamp provides power in the 320 to 800 nm range?

    <p>Tungsten filaments lamp</p> Signup and view all the answers

    What is the main function of a photodetector in the system?

    <p>Amplification of the signal</p> Signup and view all the answers

    Which of the following is a type of wavelength selector?

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

    What is one of the issues associated with using a tungsten filaments lamp?

    <p>Condensation on the glass envelope</p> Signup and view all the answers

    What is the role of a microprocessor in the given system setup?

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

    What does the Beer-Lambert law relate to?

    <p>The attenuation of light through a material</p> Signup and view all the answers

    What symbol is used to denote the intensity of light passing through the reference cell?

    <p>I0</p> Signup and view all the answers

    If the intensity I is less than I0, what does it indicate?

    <p>The sample has absorbed some of the light</p> Signup and view all the answers

    Which value in the Beer-Lambert law equation represents the absorptivity?

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

    According to the Beer-Lambert law, what is absorbance (A) proportional to?

    <p>a, L, and C</p> Signup and view all the answers

    Which equation correctly represents the relationship between absorbance (A) and transmittance (%T)?

    <p>A = log(100/%T)</p> Signup and view all the answers

    What is a major advantage of using a grating over a prism in spectroscopy?

    <p>Higher efficiency</p> Signup and view all the answers

    Which of the following best describes a cuvette's purpose?

    <p>Holds the sample being analyzed</p> Signup and view all the answers

    Which law combines the principles of Lambert, Bouguer, Bunsen, Roscoe, and Beer?

    <p>Beer's Law</p> Signup and view all the answers

    According to Beer-Lambert law, what is the relationship between the concentration of a solution and its absorbance?

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

    What elements are involved in a grating spectrometer?

    <p>Source, grating, detector</p> Signup and view all the answers

    What happens to the intensity of light as it passes through a sample with higher absorbance?

    <p>It decreases</p> Signup and view all the answers

    Which factor does not contribute to the efficiency of gratings over prisms?

    <p>Absorption effects</p> Signup and view all the answers

    What is the result of the interaction between a patient specimen and reagent in a sample?

    <p>Absorption of light selectively</p> Signup and view all the answers

    What is the main purpose of wavelength selectors?

    <p>To select portions of the power spectrum produced by the power source</p> Signup and view all the answers

    Which of the following filters absorb in the higher wavelength visible range?

    <p>Blue color filters</p> Signup and view all the answers

    What is the primary function of a collimator lens in a spectrometer?

    <p>To make sure all light rays are parallel to each other</p> Signup and view all the answers

    Which element of a spectrometer is responsible for separating light based on its wavelengths?

    <p>Diffraction grating or prism</p> Signup and view all the answers

    What type of filter is designed to be low-pass, high-pass, or band-pass?

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

    Which component of a spectrometer focuses the spectrum onto a detector?

    <p>Camera lens</p> Signup and view all the answers

    What is the function of the exit slit in a spectrometer?

    <p>Select a narrow band of wavelengths</p> Signup and view all the answers

    Interference filters are named after which aspect?

    <p>Designations based on the principle of operation</p> Signup and view all the answers

    What component of a UV-visible spectrophotometer selects a specific wavelength of light?

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

    Which light source is commonly used in the visible region (400-800 nm) for spectrophotometry?

    <p>Tungsten halogen lamp</p> Signup and view all the answers

    Which component in the UV-visible spectrophotometer holds the sample being analyzed?

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

    Which of the following ranges is covered by the ultraviolet light in spectrophotometry?

    <p>200-400 nm</p> Signup and view all the answers

    What is the function of the detector in the spectrophotometer?

    <p>Measures the amount of light that passes through the sample</p> Signup and view all the answers

    Which is NOT a component of the basic UV-visible spectrophotometer?

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

    Why are LEDs becoming popular in spectrophotometry?

    <p>They are energy-efficient and have a long lifespan</p> Signup and view all the answers

    In which application area of spectrophotometry would one study the rate of a chemical reaction?

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

    What role does the monochromator play in a UV-visible spectrophotometer?

    <p>Selects a specific wavelength of light</p> Signup and view all the answers

    Which substance is most likely to emit light in the infrared region, often used in spectrophotometers?

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

    According to the Beer-Lambert Law, which variable represents the molar absorptivity?

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

    What happens to absorbance if the concentration of the solution is doubled?

    <p>Absorbance is doubled</p> Signup and view all the answers

    Which of the following describes a major assumption of Beer-Lambert Law?

    <p>Absorbance is directly proportional to concentration</p> Signup and view all the answers

    What does an absorbance of 0 at a specific wavelength indicate?

    <p>No light of that particular wavelength has been absorbed</p> Signup and view all the answers

    Why is it important to correct absorbance measurements for the concentration of the sample?

    <p>To avoid meaningless absorbance measurements</p> Signup and view all the answers

    Which of the following is NOT a limitation of spectrophotometry?

    <p>High sensitivity</p> Signup and view all the answers

    In spectrophotometry, what would likely happen if a solution is too dilute?

    <p>Absorbance will be very low</p> Signup and view all the answers

    Which research application is commonly associated with spectrophotometry?

    <p>Protein analysis</p> Signup and view all the answers

    What is the unit of molar absorptivity?

    <p>L mol-1 cm-1</p> Signup and view all the answers

    In Beer's Law, which variable represents concentration?

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

    If the path length is doubled and the absorbance is kept constant, what happens to the concentration?

    <p>It halves</p> Signup and view all the answers

    Which of the following is a typical application of spectrophotometry?

    <p>Measurement of nucleic acids</p> Signup and view all the answers

    What was the concentration of guanosine found in the example calculation?

    <p>8.33 x 10-5 mol/L</p> Signup and view all the answers

    Which of the following is not a limitation of spectrophotometry?

    <p>It has high sensitivity and selectivity</p> Signup and view all the answers

    What is Beer's Law equation?

    <p>A = εlc</p> Signup and view all the answers

    What factor influences the proportion of light absorbed by a solution?

    <p>The number of molecules it interacts with</p> Signup and view all the answers

    Study Notes

    Definition of Spectrophotometry

    • A scientific method that measures the absorption of light by a substance at different wavelengths.
    • Wavelengths range from ultraviolet (200-400 nm), visible (400-700 nm), or near infrared (700-800 nm).

    Basic Principle of Spectrophotometry

    • Measures the concentration of solutes in a solution by measuring the amount of light absorbed.
    • Uses a cuvette placed in a spectrophotometer.

    Basic Components of UV-Visible Spectrophotometer

    • Light source: Emits light in the desired wavelength range (e.g., deuterium lamp for UV region, tungsten halogen lamp for visible region).
    • Monochromator: Selects a specific wavelength of light (e.g., filter, prism, gratings).
    • Entrance slit: Determines the width of the light beam.
    • Dispersive element: Separates the light into different wavelengths.
    • Exit slit: Allows only the selected wavelength to pass through.
    • Sample cell (cuvette): Contains the sample being analyzed (made of glass, plastic, or quartz).
    • Detector: Measures the amount of light that passes through the sample.

    Components of UV-Visible Spectrophotometer

    • Source: Provides a beam of light.
    • Filter (optional): Selects a specific wavelength range.
    • Fiber: Guides the light from the source to the cuvette.
    • Cuvette: Holds the sample being analyzed.
    • Photodetector: Detects the light that passes through the sample.
    • Readout: Displays the data.
    • Microprocessor: Processes the data.
    • Recorder: Records the data.

    Sources of Light

    • Hydrogen lamp: Emits light in the infrared region and is often used in spectrophotometers that measure absorbance in the ultraviolet region.
    • Tungsten filament lamp: Produces visible light and is used in spectrophotometers that measure absorbance in the visible region.
    • LED: Energy-efficient and has a long lifespan.

    Applications of Spectrophotometry

    • Quantitative analysis: Determines the concentration of a substance in a solution.
    • Qualitative analysis: Identifies the presence of a substance in a solution.
    • Kinetics: Studies the rate of a chemical reaction.
    • Biochemistry: Studies the properties of proteins, enzymes, and other biological molecules.
    • Environmental monitoring: Measures the levels of pollutants in the environment.

    Component Functions

    • Source of light: Electromagnetic waves.
    • Filter/prism: Spectral isolation.
    • Fiber optic: Directional control of the beam.
    • Cuvette: Holds the liquid analyte.
    • Photodetector: Amplification of the signal.
    • Readout device: Digital reading.
    • Microprocessor: Calculates the concentration.
    • Recorder: Gives the result.

    Wavelength Selectors

    • Monochromators: Devices that separate light based on its wavelengths.
    • Filters: Glass or interference filters that absorb power for specific wavelengths.

    Monochromators

    • Prisms: Refraction of sunlight.
    • Grating spectrometer: Source, grating, mirrors, detector.

    Cuvettes

    • Definition: A small rectangle, round, or square vessel.
    • Function: Holds the substance being analyzed and maintains the optical characteristic.

    Samples

    • A sample substance results from the interaction between a patient specimen and reagent.
    • Absorbs light selectively according to the law of Lambert, Bouguer, Bunsen, Roscoe, and Beer's Law.

    Beer's Law

    • States that there is a linear relationship between the concentration of a solution and the absorbance of the solution.
    • Enables the concentration of a solution to be calculated by measuring its absorbance.

    Absorbance of a Sample

    • The intensity of the light passing through the sample is referred to as the absorbance.
    • The intensity of light passing through the sample is dependent on the sample's absorbance.
    • Reflected in the cuvette surface.

    The Importance of Concentration

    • The proportion of the light absorbed depends on how strongly it interacts with the sample.
    • Concentrated solutions have higher absorbance, while dilute solutions have lower absorbance.

    Limitations of Spectrophotometry

    • Restriction to the solution phase only.
    • Cost: Spectrophotometers can be expensive.
    • Low sensitivity and selectivity.

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    Description

    Learn about the scientific method of spectrophotometry, which measures the absorption of light by substances at different wavelengths. This technique is used to determine the concentration of solutes in a solution.

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