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Chemistry 112 Copper in a Penny

Chemistry 112 Copper in a Penny - Drew Rasmussen Partner...

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Drew Rasmussen Partner: Jay Instructor: Katri Truhler Chemistry 112 Lab March 24, 2011 Colorimetric Determination of Copper in a Penny A. Research Question: a. What is the percentage of copper in the assigned penny? B. Theoretical Approach: a. From Beer’s Law we know that concentration and absorbance are directly related, thus as concentration increases absorbance will increase, and as concentration decreases, so will absorbance. With CuSO 4 * 5H 2 O a standard curve can be created by generating different stock solutions, varying only by concentration. By graphing the Absorbance vs. Concentration of our 6 standard solutions we should get a relatively linear line (and an equation for the line) that can be used to determine the percentage of copper in our penny by simple calculations, and plugging in the absorbance reading of our penny at a maximum wavelength. C. Observations and Results: a. The penny used was a 1986 penny, that was relatively clean for its age. It wasn’t too tarnished, and it was in good shape. It weighed 2.540g (+ or – 0.001g). b. Our group was assigned a stock solution of 0.100g of Copper per 250 mL. Through calculations and knowing the molecular weight of CuSO 4 * 5H 2 O, we calculated that 0.392g of the solid would have to be added to produce our
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assigned concentration. CuSO 4 * 5H 2 O is a blue crystal that looks a lot like sugar or salt. It has a very faint sweet aroma, and dissolves easily in water. When added to water it has a light opaque blue color. Ammonium hydroxide is a very potent chemical, it burned my nostrils upon wafting it (must be very concentrated). After the addition of 4.9mL of Ammonium hydroxide to our Copper and Water solution, the entire solution became a very deep royal blue color. Once diluted to the 250mL mark on the volumetric flask it was a bit lighter in appearance, but had the same general color. Our standard solution produced an absorbance of 0.369. When the nitric acid was poured on the penny, bubbles began forming rapidly shifting the penny throughout the liquid. This was a very violent reaction causing a Turquoise liquid to form as the concentrated acid dissolved the penny. As the penny was dissolving copper colored smoke was coming out of the beaker. As the reaction is coming to an end, the smoke
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Chemistry 112 Copper in a Penny - Drew Rasmussen Partner...

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