was added. The pennies were dissolved by this solution in a reaction that lasted roughly ten minutes. The contents of these beakers were then added to 100 mL volumetric flasks by the method of quantitative transfer. 14mL of concentrated ammonia solution was then added to each flask. 1mL of ammonia was again added until no solid remained. The volumetric flask was then diluted to volume. Absorbance Measurements-Cuvettes were then filled ¾ full with the six standard solutions and the three penny solutions. Using the spectrometer a calibration curve was created using five standard solutions. The 0.00mL Cu2+ solution was not used for the curve but was used to find the wavelength needed in the curve. This tells the spectrometer what wavelength of light to pass through the solution.Calculations- Concentration of Cu2+ solution in each standard solution was the first thing calculated. To do this, the volume of Cu2+ solution is multiplied by the density of Cu2+ solution and then divide by the total volume of standard solution. The next calculation was done to find the equation of the calibration curve; this was completed using the linear regression in loggerpro. Using this equation and the found absorbance of each penny solution, the concentration of copper in each penny solution could be 2
Condition Penny Mass (g) Concentration Cu in Penny Absorption (AU) Grams Cu in Percent Cu in
Standard Deviation Standard deviation of mean T-test result Government regulated % Cu 2.29% .461 .266 Not significantly different 2.50% Table (8-2)
DiscussionThe three pennies studied contained less copper than the government mandated 2.5%. However a T-test shows that there is no significant difference when comparing the percent copper found in the three pennies and the government mandated percent copper in a penny. This T-test was performed at the 95% confidence level. Copper is located on the outside of the penny. The lower amount of copper in each penny can be attributed to the wear and tear of the outer parts of the penny. The older the pennies are the more scratches and dents they accumulate and this results in a lower amount of copper in the penny. This is shown as each penny studied has a higher amount of copper as the year minted increases. One source of potential error is in the calibration curve. If this curve is
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- Fall '08