Week 4: The Spectra of Conjugated Dyes and Investigation of Beer's Law Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Goals This experiment illustrates the molecular basis for color and the complementary relationship between the perceived color of a solution and the color of light absorbed. In the first part of this week's lab, you will measure the absorption spectra of two conjugated dyes and compare the results to the theoretical predictions of a particle-in-a-box model. In the second part of the experiment, you will identify the food dyes present in a sample of Koolaid or Gatorade from the absorption spectrum and paper chromatography. Finally, you will use Beer's Law to determine the concentration of food dyes in your sample of drink mix. To Learn or Review Light, waves, frequency, and energy Zumdahl, pp. 503-511 Particle in a Box Zumdahl, pp. 524-530 Beer's Law and Spectrometers Zumdahl, pp. A18-A20 Introduction This week's lab explores the origin of color in dye molecules. The first experiment relates the visible absorption spectrum of a dye to the particle-in-a-box model. The second experiment investigates the identity and quantity of food dye(s) that make Gatorade green or grape Koolaid purple. The introduction in your lab manual contains a great deal of background material, outlined below: 1. Origins of color, in materials like dyes 2. Particle-in-a-box model 3. Structure of the conjugated dyes in the first experiment 4. Beer's Law, which relates concentration of a dye and absorbance of light 5. Description of paper chromatography
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