11.1: Instructor Guidelines
- Page ID
- 118018
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Students are introduced to spectrophotometry during this lab. Students will learn how to use the spectrophotometer to determine the specific dyes present in different colored candies (Skittles). The purpose of this introductory lab is to prepare students for more advanced use of the spectrophotometer in future labs.
Tasks
Students will complete the following during this lab:
- Extract federally approved food dye from each color of Skittles candy (original flavors, red packaging).
- Blank and use the spectrophotometer to measure absorbance for each dye.
- Use the derived absorbance values to determine which dye(s) are present in each of the colored candies.
Lab instructors should provide students with an introduction to spectrophotometry and the absorbance spectrum (x-axis vs. y-axis). Review the relationship between absorbance and transmittance, as well as the range of wavelengths found in the visible spectrum. Students may not know that red light has a longer wavelength (lower energy) than violet light (higher energy). Provide students with examples of how to calculate absorbance if given percentage transmittance, and vice versa.
We will be using newer spectrophotometers compared to the image found in the student introduction (Chapter 11.1, Figure 2). The spectrophotometers students will be working with are the ThermoFisher Spectronic 200 models. Please introduce students to this instrument and show students where to place cuvettes, how to blank the spectrophotometer, and how to measure absorbance for each sample.
Remind students to make sure the light from the spectrophotometer does not pass through the frosted side of the cuvettes. Students can use Kimwipes wipe the clear side of each cuvette before each reading.