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MethodsSolution PreparationThe first step of this lab was to create six dilutions of copper from a stock solution of copper II. In order to do so, six 50 mL volumetric flasks were each filled with 0.00 mL, 2.00 mL, 4.00 mL, 6.00 mL, 8.00 mL, and 10.00 mL of stock Cu2+solution using a pipet. Then to
Thompson 3each flask 3 mL of ammonia was added to dissolve all the solid and then each flask was subsequently filled to the 50.0 mL mark with distilled water. For the copper solution from the penny, first the penny was massed and observed for date and wear. Then the penny was placed in a 150 mL beaker along with 25 mL of 6 M nitric acid. Once the entire penny was dissolved, the contents of the beaker were transferred to a 100 mL volumetric flask quantitatively. Subsequently, 14 mL of ammonia were added to the volumetric flak and thenmore was added 1 mL at a time until the solution became transparent. Finally, the flask was filled to the 100 mL mark with distilled water.Absorbance MeasurementOnce the MeasureNet system was ready, the colorimeter was set to the red wavelength because the maximum wavelength of absorbance was about 630 nm, and the 0.00 mL dilution of copper II was placed in the reference slot and the sample slot to calibrate the colorimeter. Then each of the stock dilutions was placed in a cuvette and the absorbance of each of those was recorded compared to the 0.00 mL (clear) dilution. Finally, the solutions from each penny were placed in a cuvette and the absorbance of each of those was recorded.CalculationsA calibration curve was created using the known concentrations of the stock dilutions and the absorbances recorded for each. Then, a trend line was added to the graph with the equation:y=0.790x+0.0046Where y is the absorbance and x is the concentration of the solution. From the equation of the trend line and using the recorded absorbance of each penny the concentration of the penny solutions was extrapolated in grams per liter. Then, using the total volume of the MintYearConditionAbsorbanceConcentration(g/L)Mass of Penny(grams)Penny 12005Worn, blue spots0.4920.6232.4196Penny 21986Dark brown0.4930.6182.4772Penny 32007Good condition0.5550.6962.4930Penny 42006Shiny, somescratches0.670.8422.5057
Thompson 4volumetric flask used to create the solutions, 100 mL, the total mass of copper in a penny was calculated using the equation:C oncentration(¿gL)×litersof measured solution∈flask=gCuResultsIn this lab it was determined that the average percentage of copper in a penny is 2.80%. There was no trend found between the percentage of copper and the mint year of the penny or between the percentage of copper and the condition of the penny. The T-test results showed that there was no statistical difference between the accepted value for the amount of copper in a penny and the experimental value found.Table 1: Physical and experimentally determined attributes of pennies 1 through 4Table 1 shows the year that each penny was produced as well as the physical condition of the penny as far as wear and oxidation. The mass of the penny was found before the experiment was carried out and the absorbance and concentration were found