The new Vernier Spectrometer allows students to do a wide variety of new lab investigations. To highlight some of its many capabilities, we walked down to the nearest grocery store and picked up a few products to test. We analyzed the visible light absorbance spectrum of various food colorings to see if we could identify the FD&C dyes used in a popular brand of mouthwash. By comparing the “fingerprint” of the food colorings with the absorbance spectrum of mouthwash, it was easy to determine that the color of the mouthwash was a mixture of blue and yellow dyes, which was confirmed by the information on the label.
To complete our experiment, we mixed a bit of the blue and yellow food coloring solutions to try to mimic the green color of the mouthwash. We matched the color pretty closely, and the activity gave us a theme for this investigation—green liquids.
Download Visible Spectra of Commercial Dyes Revisited (60.3 KB PDF)