copper-penny-report

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Washington State University *

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Jan 9, 2024

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Studocu is not sponsored or endorsed by any college or university Copper Penny report General Chemistry (Cornell University) Studocu is not sponsored or endorsed by any college or university Copper Penny report General Chemistry (Cornell University) Downloaded by Jeff Tricksy (jefftricksy@gmail.com) lOMoARcPSD|32735920

Copper Penny Report Natalia Jordan TA: Sewon Oh December 12th, 2020 Downloaded by Jeff Tricksy (jefftricksy@gmail.com) lOMoARcPSD|32735920

Ⅰ . Abstract This lab was designed to determine the amount of copper in a post-1982 U.S penny through the process of spectrophotometry. By using the same cuvette, absorbance is directly proportional to concentration, and the graph of those variables demonstrates Beer’s Law. The penny was first dissolved using nitric acid followed by ammonium hydroxide. This newly made copper (II) tetraamine complex is referred to as the “Penny solution” and its absorbance at 620 nm was measured. The absorbance was 0.639. The second part of the experiment was conducted to measure the absorbance of 5 different concentrations of Cu(NH3)4+. A standard curve for the concentration of Cu(NH3)4+ was generated from these values, and the concentration of Cu(NH3)4+ in the “penny solution” was determined to be 0.012978 M using the equation of the trendline from the standard curve graph. The mass of copper was then determined to be Cu from the known molarity and volume of the Cu(NH3)4+ . The percent of error was .08247 g 0 determined by comparing the measured mass of copper in the penny to the actual mass of copper in a post-1982 penny, 0.0625g Cu (found from usmint.gov). The percent error was found to be 31.95%. Ⅱ . Experimental Section Part One: First, a post-1982 penny was obtained and weighed to the nearest milligram. A 25 mL graduated cylinder was used to measure out 15 mL of concentrated nitric acid in the hood. The penny was then laid flat on the bottom of a 200 mL beaker and the 15 mL of nitric acid were slowly added, in the fume hood, on top of the penny. Because all of the copper solutions did not completely dissolve, the contents of the beaker were carefully swirled to ensure that all copper dissolved. The solution initially appeared to be a green/teal color, then became lighter, and then emitted an orange/brown gas. To the beaker, 15 mL of distilled water were added. The contents of the beaker turned from a green color to an aqua blue color. Another beaker was obtained and 25 mL of concentrated ammonium hydroxide was added to the nitric acid solution in portions. The beaker contents were then swiftly swirled after each addition of the ammonium hydroxide. After the first addition of ammonium hydroxide, the solution turned a dark blue and became cloudy after the contents were swirled. In the second addition, the beaker Downloaded by Jeff Tricksy (jefftricksy@gmail.com) lOMoARcPSD|32735920

contents became warm to the touch and a precipitate was visible in the beaker. In the third addition, the solution became a darker blue color. Lastly, in the final addition of ammonium hydroxide, a precipitate no longer remained and the beaker appeared a clear cobalt blue color. The solution was then left alone to cool to room temperature and 100 mL of copper (II) tetra ammonia complex were measured in a volumetric flask and diluted with distilled water to the mark. The solution in the volumetric flask was mixed by inversion several times to ensure it was properly mixed. This solution was labeled the “Penny Solution''. The absorbance of this solution was measured at 620 nm. Part two: Five beakers were thoroughly cleaned and dried. The beakers were labeled 1-5. The first beaker was used to obtain 15 mL of .040 M Cu(NH 3 ) 4 + . A series of 5 serial dilutions was conducted. A volumetric pipette was used to dispense exactly 10.00 mL of distilled water into each of the four beakers labeled 2,3,4, and 5. From beaker 1, a volumetric pipette was used to measure exactly 10.00 mL of the Cu(NH 3 ) 4 + stock solution and it was added into beaker 2. The solution in beaker 2 was swirled to ensure proper mixing. A volumetric pipette was then used to move 10.00 mL of the solution in beaker 2 into beaker 3. The solution in beaker 3 was swirled to ensure proper mixing. A volumetric pipette was then used to move 10.00 mL of the solution in beaker 3 into beaker 4. The solution in beaker 4 was swirled to ensure proper mixing. A volumetric pipette was then used to move 10.00 mL of the solution in beaker 4 into beaker 5. The solution in beaker 5 was swirled to ensure proper mixing. After the 5 serial dilutions were performed, the absorbance of the solution in each of the 5 beakers was determined and recorded at 620 nm. Ⅲ . Results and Discussion: Downloaded by Jeff Tricksy (jefftricksy@gmail.com) lOMoARcPSD|32735920

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