The equation of the line was used to calculate the concentration of each penny solution by plugging the absorbance measurements in for “y”. In Microsoft Excel, the grams of copper that were originally in the penny were calculated. The percent Cu for each penny was found in Microsoft Excel using the mass of each penny. The mean percent Cu and the standard deviation were also calculated in Microsoft Excel. Results
Thomas 4 The concentration and absorbance of each stock solution is displayed in Table 1. Stock Solution (mL) Concentration (g/L) Absorbance Wavelength (nm) 0.000 0.00 - 608.00 0.020 2.00 0.256 0.040 4.00 0.431 0.060 6.00 0.564 0.080 8.00 0.711 0.100 10.00 0.989 Table 1: Standard Solution The calibration curve was found using the linear regression function on Logger Pro . Calibration Curve for the Standard Solutions Figure 1 The following table gives the absorbance of each penny that was calculated from the spectrophotometer. Penny 2, the penny that was minted most recently (in 2002) has the highest absorbance. Absorbance
Thomas 5 Penny 1 0.528 Penny 2 0.538 Penny 3 0.529 Table 2 Table 3 shows the data from the 3 pennies that was calculated using a spreadsheet on Microsoft Excel. Year Concentration (g/L) g Cu Mass (g) % Cu Mean % Cu Standard Deviation Penny 1: 1997 0.528 0.0528 2.486 2.12% 2.13% 0.0265 Penny 2: 2002 0.540 0.0538 2.488 2.16% Penny 3: 1997 0.5298 0.0529 2.507 2.11% Table 3 The following table shows that statistics test used to compare the currently mandated Cu content with the results of this experiment. Average Mass % Cu Accepted Value T-Test Value at 95% Confidence Level S m T-Test Right Side T-Test Left Side Significantly Different 2.13% 2.5 4.3 0.01527 0.0656 0.37 Yes Table 4 Discussion The T-Test at 95% confidence level indicated that the 2.13% Cu found in the sample pennies was significantly different than 2.5% Cu predicted in the hypothesis. While the % mass value determined by the tested pennies was somewhat close to the accepted value of 2.5%, the T-Test suggest that the copper content was not in agreement
Thomas 6 with the accepted value. This evidence does not support the hypothesis that all pennies minted after 1982 would contain 2.5% copper content.
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- Fall '08