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Investigation 3 – PostLab









  • Complete the Analysis Questions in your SDR then discuss them as a class.
  • How does the absorbance and transmittance of each wavelength of light determine the color of a transparent object? 
  • Graph: Create a separate absorption spectrum for each colored solution (red, green, and blue) to show the relationship between the wavelength of light and the amount of light each solution absorbed. Sample graphs provided.
    • Indicate the wavelengths you measured along the x-axis.
    • Create a scale of absorbance values along the y-axis.
    • Connect the data points.

  • What pattern do you see between the absorption spectra and the color of the solution? 
  • Why do you think the blue and green spectra both have peaks in the 550-700 nm range while the red spectrum peaks in the 400 to 550 nm range?
  • Why do you think the absorption spectra graph for the green solution has two peaks?

Note: Questions marked with a triangle (∆) are included to enrich your understanding. These questions do not appear in your SDR but might be used as additional discussion points during the PostLab.

  •  What do you think the transmittance graphs would look like for each solution? 

Think back to the first Investigation when you used the spectrophotometer. Remember that you set the spectrophotometer at 630 nm in order to determine the concentration of the green-colored water.

  •  Why do you think the spectrophotometer was set at 630 nm? 
  •  If you take a close look at the graph for the green food coloring you’ll notice that it contains two absorption peaks. What conclusions can you draw? 
  • What conclusions can you draw about the colors of opaque objects? Explain your answer. 

  • Why does mouthwash appear blue or green? Why does orange juice appear orange?



Complete the Focus Question in your SDR then discuss it as a class. Use the suggested response below to guide students’ answers.

  • How does wavelength affect the perception of light?