Experiment 3 - Formal Lab

Experiment 3 - Formal Lab - Experiment 3 Determining...

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Experiment 3 – Determining Sunscreen Effectiveness using Spectroscopy Chemistry 1A GSI: Jennifer Yen Purpose : Observe the correlation between the effectiveness of a sunscreen and its extinction coefficient. Compare two different brands of sunscreen in their ability to absorb UV rays and efficiency in protecting the surface of which they cover. Methods : Six dilutions of stock solution with different concentrations were prepared using 2- propanol (Table 1). Each dilution was ran at 310nm through the UV spectrometer, which recorded the absorbance of UV light versus the concentration of each dilution (Table 1). According to Beer’s Law (A = ε l C), the extinction coefficient ( ε ) of the stock solution could be calculated since the absorbencies for the corresponding concentrations (C) were already known. A Beer’s law plot (absorption vs. concentration) (Graph 1) was made, and the slope (extinction coefficient) of the plot was found by using linear regression on a calculator. Extinction coefficients of other groups with different SPF stock solutions were obtained and compared (Table 2, Graph 2). 5 UV sensitive disks of assorted colors were placed on a white sheet of paper. The UV lamp was placed 6 inches above UV disks and turned on for 2 minutes. Orders of intensity, appearance of color, and disappearance of color were recorded (Table 3). 5 UV sensitive disks of the same color (blue) were placed on a white sheet of paper. One disk was used as a control; the other disks were divided into 2 groups: Walgreens and Coppertone. Three trials were run for each of the three SPFs; new sunscreen was used for all the trials, and disks were washed after each trial. After 2 minutes under the UV lamp, the brand with
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Experiment 3 - Formal Lab - Experiment 3 Determining...

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