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Experiment3 - Kimberly Roberts March 4 2009 Chemistry 1A...

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Kimberly Roberts March 4, 2009 Chemistry 1A Section: #410 Son Nguyen Experiment #3: Molecules and Light Purpose Investigation 1: Molecular Spectroscopy The goal of this half of the experiment is to determine the effectiveness of a sunscreen product by measuring extinction coefficient of its active ingredient through the use of a molecular spectroscopy machine. Investigation 2: Putting Sunscreens to the Test The goal of the second half of the experiment is to determine the effectiveness of sunscreens using UV sensitive disks and UV light. This is to determine if one SPF is more effective absorbing UV light. Method Investigation 1: Molecular Spectroscopy First, begin by gathering two burettes, one designated to the stock solution and the other to the 95% 2-propanol. Rinse each of the burettes with their respective solutions twice, assuring that is the only solution present, and afterwards fill each of them with the solution making sure to clear any air bubbles (this may skew results). Next, gather six small test tubes and clean them with 95% 2-propanal and dry them with a Kim- Wipe. This step is to help ensure that debris or fingerprints do not interfere with the reading from the mass spectroscopy system. The next step is to create the six different dilutions of the stock solution with the 95% 2-propanol. The goal is to make solutions that cover a range of concentrations. For example one test tube of 3.00mL of the stock solution only, another of 2.50mL of the stock solution with 0.50mL of 95% 2-propanol, etc. After preparing your solutions, run each through the spectroscopy unit, and record the absorbency of each.
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Spectroscopy passes light at the solution and counts the return of photons on the other end. Depending on the concentration of the active ingredient, 95% 2-propanol, the absorbency intensity will change.
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