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experimentally using the colorimeterTable 2: Calculated attributes of pennies 1 through 4Table 2 shows the calculated grams of copper found in each penny using the concentration and the percentage of copper found in each penny, which was found using the equation:gramsof copper∈pennymassof penny(grams)=copper∈pennyTable 2 also shows the average percentage of copper found in the pennies found by calculating the mean of the four values.Figure 1: Calibration Curve from diluted stock solutions with penny concentrations markedGrams of Copper in Penny% CopperAverage %CopperStandardDeviationPenny 10.06232.57%2.80%.608%Penny 20.06182.49%Penny 30.06962.79%Penny 40.08423.36%
Thompson 126.96.36.199.188.8.131.52.80.9184.108.40.206.220.127.116.11.70.80.9f(x) = 0.79x + 0R² = 1Calibration CurveabsorbanceLinear (absorbance)Penny 1Penny 2Penny 3Penny 4Concentration (g/L)AbsorbanceFigure 1 shows the calibration curve obtained from the known concentrations and experimentally determined absorbance of the diluted stock solutions. It also shows where each of the pennies concentration falls on the graph when calculated using the linear equation obtained from the curve.Discussion
Thompson 6The currently mandated amount of copper in a penny is 2.5% by mass. In this lab, the pennies had a calculated average of 2.80% copper by mass, which is a difference of .3% from the mandated amount. However, using the T-test at the 95% confidence level, it was determined that the difference between the mean and the mandated amount was not significant statistically because .3 is not greater than .966. Surprisingly, the older pennies did not have a higher percentage of copper compared to the newer pennies; in fact one of the newest pennies from 2006 had the highest percentage of copper at 3.36% (Table 1 & Table 2). This is likely because the government mandated amount hadn’t changed since 1982 and all the pennies were from after that time. The more worn pennies that were a deeper brown or had oxidized spots did tend to have lower percentages of copper (Table 1 & Table 2). It is possible that this penny had such a high percentage of copper because the penny was so new and not nearly as worn as the other pennies therefore retained more of the copper that originally coated the penny.There could have been possible error when the penny was dissolved if all of the solidin the solution was not dissolved using the ammonia, which would have resulted in a lower percentage than there should have been. Additionally, if the solution was not properly transferred from the beaker to the volumetric flask and some of the solution was lost, more of the copper would have been lost, which also would have resulted in lowered readings. Another possible source of error was the different amounts of wear on each penny. Becausepennies are zinc with an outer shell of copper, if the outside of one penny was worn to a great degree or was partially oxidized, the experimentally determined amount of copper on the penny would be lower because the penny would likely have already lost some of its copper content.