Lab Project on Topic of the Relationship Between Light Absorbance and Color

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So far for the lab project our goals have been to figure out how to use the piece of equipment called the spec 20 to figure out the relationship between light absorbance and color. In this case we used red and blue food coloring, and then mixed the two which gave us purple. We also were required to use the spec 20 to find the amount of phosphoric acid in cola beverages.

After gathering data we placed our conclusions on scatterplots to see the relationships between absorbance and wavelengths with the different mixtures as well as the percent transmittance and wavelength relationship. After making our mixture by adding one drop of red food coloring to 100mL of water. The red food coloring had an analytical wavelength of 523 nm and shows the maximum absorbance at. 70 according to Figure 2. In Figure 1 however, the percent transmittance has an analytical wavelength of 522 nm and showed a minimum percent transmittance of 20. 25%. After mixing one drop of blue food coloring with 100 mL of water we concluded after using the spec 20 that the analytical wavelength was shown to 628 nm and had a maximum absorbance of 1. 82 as shown on Figure 4. Figure 3 shows the minimum percent of transmittance at 1. 55% for the relationship between transmittance percent and blue food coloring regarding wavelength. We then mixed another solution containing one drop of red and one drop of blue food coloring into 100mL of water which was a purple solution.

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The analytical wavelength was 627 nm and it had a maximum absorbance of 2. 50 according to Figure 6 and a minimum percent transmittance of 1. 53 according to Figure 5. Lastly we made a dilution containing KMnO4 which we diluted with water. The analytical wavelength stayed constant at 550nm. Figure 8 shows the percent transmittance of the five concentrations whereas Figure 7 shows the percent transmittance of the five concentrations. Scientific ExplanationAccording to Dr. Anne Marie Helmentsine “Beer's Law is an equation that relates the attenuation of light to properties of a material. The law states the concentration of a chemical is directly proportional to the absorbance of a solution. The relation may be used to determine the concentration of a chemical species in a solution using a colorimeter or spectrometer The relation is most often used in UV-visible absorption spectroscopy. ”

After going over data and studying the charts and the pictures we took after finding absorbance and transmittance using the spec 20 I concluded that a scientific error was made regarding the graphs. The graphs look to have shifted during some point during the experiment or possibly it was human error while making them in excel. Fortunately we took pictures of the spec screen after each trial so I used those numbers from the pictures I took to clarify some confusion. A lot of the numbers look accurate but a couple on the graphs were questionable which is why I wanted to clarify.

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