Visible Light Spectrum and Spectrophotometry
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Visible Light Spectrum and Spectrophotometry

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Questions and Answers

How does atomic absorption spectrophotometry (AAS) determine the concentration of a sample?

  • By calculating the reflectance of the sample
  • By measuring the emitted light after atomization
  • By detecting the amount of UV light transmitted
  • By measuring the light absorbed by an atom (correct)
  • What is a primary clinical application of flame emission spectrophotometry (FES)?

  • Determining molecular weight of proteins
  • Measuring electrolytes like Na and K (correct)
  • Analyzing trace metals in tissues
  • Detecting impurities in colorless solutions
  • What light source is used in atomic absorption spectrophotometry?

  • Xenon flash lamp
  • Incandescent bulb
  • Hollow-cathode lamp (correct)
  • Laser diode
  • Which of the following best describes the Beer-Lambert law?

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

    What principle does infrared spectrophotometry primarily measure?

    <p>The vibrational spectrum of molecules</p> Signup and view all the answers

    In flame emission spectrophotometry (FES), how is concentration determined?

    <p>By measuring the emitted light from excited atoms</p> Signup and view all the answers

    Which technique is generally considered obsolete due to the development of ion selective electrodes (ISE)?

    <p>Flame emission spectrophotometry</p> Signup and view all the answers

    Which type of spectrophotometer is primarily used for measuring colorless solutions?

    <p>UV light spectrophotometer</p> Signup and view all the answers

    What is the wavelength range of visible light?

    <p>350-700 nm</p> Signup and view all the answers

    Which type of cuvette is most suitable for a UV light spectrophotometer?

    <p>Quartz cuvettes</p> Signup and view all the answers

    What is the purpose of the photomultiplier tube (PMT) in a spectrophotometer?

    <p>To convert light into electrical energy</p> Signup and view all the answers

    Which spectrophotometer type uses one beam of light and measures only one sample at a time?

    <p>Single beam spectrophotometer</p> Signup and view all the answers

    How does a double beam spectrophotometer improve accuracy?

    <p>It uses two beams to eliminate light fluctuations.</p> Signup and view all the answers

    What does the readout system in a spectrophotometer provide?

    <p>Display of the output from the photodetector</p> Signup and view all the answers

    Which color corresponds to the wavelength range of 651-700 nm?

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

    What does lambda max (λmax) signify in spectrophotometry?

    <p>The wavelength of maximum absorbance of a substance</p> Signup and view all the answers

    What is the principle behind photoelectric colorimetry?

    <p>It uses a filter to isolate a specific wavelength of light for analysis.</p> Signup and view all the answers

    How is the concentration of an unknown solution in a photoelectric colorimetry setup calculated?

    <p>By taking the ratio of absorbance of the unknown to the concentration of the standard.</p> Signup and view all the answers

    Which of the following solutions can a spectrophotometer analyze that a photoelectric colorimeter cannot?

    <p>Both colored and non-colored solutions.</p> Signup and view all the answers

    What does the Beer-Lambert Law relate to in spectrophotometry?

    <p>The relationship between absorbance and concentration.</p> Signup and view all the answers

    What type of light sources can spectrophotometry utilize that photoelectric colorimetry cannot?

    <p>Both UV and infrared light.</p> Signup and view all the answers

    In spectrophotometry, what is the role of the monochromator?

    <p>To disperse white light into a spectrum of colors.</p> Signup and view all the answers

    What is the primary difference between a spectrometer and a colorimeter?

    <p>Colorimeters use filters, while spectrometers use monochromators.</p> Signup and view all the answers

    What aspect of a solution is measured by a spectrophotometer to determine concentration?

    <p>Light transmittance.</p> Signup and view all the answers

    Study Notes

    Band of Visible Light

    • Visible light ranges from 350 to 700 nm.
    • Color spectrum includes:
      • Violet (350-430 nm)
      • Blue (431-475 nm)
      • Green (506-555 nm)
      • Yellow (576-600 nm)
      • Orange (601-650 nm)
      • Red (651-700 nm)
    • Specific color wavelengths:
      • Green-blue (476-495 nm)
      • Blue-green (496-505 nm)
      • Yellow-green (556-575 nm)

    Spectrophotometer Components

    • Sample Cells (Cuvettes):

      • Made of glass or quartz, hold colored solutions.
      • Must be scratch-free for accurate light passage.
      • Glass cuvettes are used for visible light; quartz for UV light.
    • Light/Photo Detector:

      • Converts transmitted light energy into electrical energy.
      • Common types: photocell, phototubes, photomultiplier tubes (PMT).
      • PMT is preferred for its sensitivity and rapid response.
    • Readout System:

      • Displays output from the photodetector.
      • Formats include meters, galvanometers, LED displays.

    Types of Spectrophotometers

    • Single Beam Spectrophotometer:

      • Uses one light beam; measures at wavelengths from 325 nm to 1000 nm.
      • Reads test samples and blanks sequentially.
    • Double Beam Spectrophotometer:

      • Operates from 185 nm to 1000 nm; splits light into two beams.
      • One beam for reference and the other for sample, minimizing error.

    Applications of Spectrophotometers

    • Analyzes solution concentration qualitatively and quantitatively.
    • Requires unknown concentration to fall within the standard curve range.

    Standard Curve

    • Example table shows concentration (mg/dl) vs. absorbance:
      • Concentrations of 60, 70, 80, 90, 100, 110 correlating with specific absorbance values.

    Finding Unknown Concentration

    • Formula: Concentration of unknown = (Au/As) x Concentration of standard
      • Au: absorbance of unknown
      • As: absorbance of standard

    Photoelectric Colorimetry

    • Principle:
      • White light through a filter only allows specific wavelengths.
      • Colored solution absorbs some light; transmitted light strikes a photoelectric cell which converts it to electrical energy.
      • Outputs percent transmittance or absorbance.

    Spectrophotometer Overview

    • Combination of spectrometer and photometer; measures light absorption to determine concentration.
    • Can analyze colored and non-colored solutions using visible, UV, and infrared light.

    Spectrophotometer Measurement Principle

    • Light passes through a monochromator, creating a spectrum.
    • Sample absorbs light; remaining light strikes a detector to quantify absorbance or transmittance.

    Additional Spectrophotometric Applications

    • Analyzes reaction rates (e.g., enzyme analysis).
    • Determines molecular weights of substances.
    • Detects impurities in solutions.

    Atomic Absorption Spectrophotometry (AAS)

    • Measures concentration based on light absorption by atoms, not molecules.
    • Uses hollow-cathode lamp; atomizes samples via flame.
    • Sensitive technique, ideal for trace metals (e.g., magnesium, copper, lead, calcium).

    Flame Emission Spectrophotometry (FES)

    • Measures emitted light from excited atoms post-atomization by flame.
    • Emission color correlates to specific metal ions (e.g., red for lithium, yellow for sodium).
    • Primarily measures electrolytes (Na, K, Li).

    Infrared Spectrophotometry

    • Measures vibrational spectra of samples using infrared radiation.
    • Records absorbed frequencies and their extent.

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    Description

    Explore the band of visible light from 350 to 700 nm with this quiz. Test your knowledge on the colors associated with specific wavelengths and the basic components of a spectrophotometer. Enhance your understanding of light absorbance in various substances.

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