Percent Copper In Brass Lab Report

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Percent Copper In Brass Lab Conclusion
Emily Oleisky
The purpose of this lab was to observe the amount of light a solution absorbs, and use the relationships in the Beer-Lambert Law to determine the quantity of a certain compound within a complex sample. First, the relationships between wavelength, concentration, and absorbance were determined. This lab focused on identifying the absorption of copper in various brass samples, and finding the percent copper in brass. In the first activity of the lab, the scientist was trying to determine the difference in molar absorptivity across various wavelengths of multiple salt solutions. For this portion of the lab, relying on her knowledge of the visible light spectrum and color absorption, the scientist
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Nitric acid and brass pellets (copper) were set to react under a fume hood. The scientist observed the once liquid acid turning a green color, and the release of an orange gas due to violent fizzing/bubbling on the surface of the copper pellets: a chemical reaction. Because nitric acid is a very strong acid that is weakly bonded, it violently reacts with the metal. After about 30 minutes, the scientist noted the once clear liquid was now a dark, rich, blue aqueous Copper (II) Nitrate solution. While the solution at first appeared homogenous, the scientist noted the presence of 4 - 1mm small dark lumps, unreacted brass. From here, the scientist utilized the colorimeter to find the absorbance of this solution in collusion with the absorbance plot for Copper (II) Nitrate solutions of various molarities. From the linear fit of the Beer’s Law plot, calculations for the determination of the molarity and percent mass of copper were executed. Because the absorbance and concentration variables have a direct relationship in the Beer’s Law Equation, the linear fit was an accurate method for calculating the unknown. From the graph, it was observed that as the concentration (or molarity) of the Copper (II) Nitrate solution increased, the absorbance of the solution increased. The scientist was able to relate this finding back to her conclusions from the previous activity to realize that the dark the shade of blue, the less color variance that was reflected and the higher the absorbance. This idea is supported upon recalling that a clear solution reflects all colors: the lighter the solution color, the more light is reflected, the lower the

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