Worksheet: The Beer–Lambert Law

In this worksheet, we will practice calculating concentrations from UV–vis spectra, using calibration curves or molar extinction coefficients.

Q1:

Which of the following is a false statement about molar absorptivity coefficients?

  • AMolar absorptivities will be the same for each peak, regardless of wavelength, for a given molecule’s UV–vis spectrum.
  • BMolar absorptivity coefficients for organic molecules are typically 10,000 M−1⋅cm−1.
  • CMolar absorptivity coefficients are calculated based on absorbance and concentration.
  • DMolar absorptivities can be used to compare the ability to absorb light at a given wavelength of different chromophores.

Q2:

The regression line from a plot of absorbance versus concentration yields 𝐴=2.31𝑐+0.002. If the absorbance of an unknown is measured to be 0.124, what is the concentration of the analyte?

Q3:

Fill in the blank. The relationship between the analyte concentration and the intensity of measured radiation from thermal excitation methods, such as a flame or plasma, is .

  • Aparabolic
  • Blinear
  • Casymptotic
  • Dpolynomial
  • Eexponential

Q4:

Fill in the blank: Background correction in flame atomic absorption spectroscopy can minimize the effect of .

  • Areactions between the analyte and matrix
  • Bscattering and absorption by the matrix of the analyte
  • Cnonvolatilization of the analyte
  • Dionization of the analyte

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