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In-class Questions: General Background on Molecular Spectroscopy

  • Page ID
    96075
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    Electromagnetic Radiation

    1. What is the relationship between the energy (E) and frequency (\(\nu\)) of electromagnetic radiation?
    2. What is the relationship between the energy and wavelength (\(\lambda\)) of electromagnetic radiation?
    3. Write the types of radiation observed in the electromagnetic spectrum going from high to low energy. Also include what types of processes occur in atoms or molecules for each type of radiation.

    Beer’s Law

    1. What factors influence the absorbance that you would measure for a sample? Is each factor directly or inversely proportional to the absorbance?
    2. If you wanted to measure the concentration of a particular species in a sample, describe the procedure you would use to do so.
    3. Suppose a small amount of stray radiation (PS) always leaked into your instrument and made it to your detector. This stray radiation would add to your measurements of Po and P. Would this cause any deviations to Beer's law? Explain.
    4. The derivation of Beer's Law assumes that the molecules absorbing radiation don't interact with each other (remember that these molecules are dissolved in a solvent). If the analyte molecules interact with each other, they can alter their ability to absorb the radiation. Where would this assumption break down? Guess what this does to Beer's law?
    5. Beer's law also assumes purely monochromatic radiation. Describe an instrumental set up that would allow you to shine monochromatic radiation on your sample. Is it possible to get purely monochromatic radiation using your set up? Guess what this does to Beer's law.
    6. Is there a disadvantage to reducing the slit width?
    7. Consider the relative error that would be observed for a sample as a function of the transmittance or absorbance. Is there a preferable region in which to measure the absorbance? What do you think about measuring absorbance values above 1?
    8. What are some examples of matrix effects and what undesirable effect could each have that would compromise the absorbance measurement for a sample with an unknown concentration?

    This page titled In-class Questions: General Background on Molecular Spectroscopy is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Thomas Wenzel.