Spectra of Conjugated Dyes & 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		Applets Spectral Colors This applet allows you to manipulate the absorbance or transmission vs. wavelength plot of a visible absorption or transmission spectrum and observe the color of a solution with the spectrum that you create. Electrons-in-a-box This applet provides an interactive energy level diagram for a one-dimensional particle-in-a-box. You can change the length of the box, the mass of the particle, and the number of electrons confined to the potential "box" to model the ground and excited state of different conjugated dye molecules. You can also plot the one dimensional wavefunctions for each energy level. Technique Links Spectrometer: Analog Spectrometer: Digital Spectrometer: Scanning Pipet Volumetric Flask 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. Key questions What makes a red solution, like cherry Koolaid, appear red to your eye? What colors of light are absorbed and what colors are transmitted? How are absorbance and transmission spectra related? What is the scanning spectrometer doing, when it measures the spectrum of a solution? What steps must it automate from the procedure you used to measure a "point-by-point" spectrum with a Spec 20? What are the approximations made in applying the particle-in-a-box model to the electron energy levels of conjugated dyes? How well do these approximations work?
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