For my Chemistry lab, we were asked to determine the amount of copper and zinc in coins older than 1983 and newer than 1984. Since starting in 1983, some U.S. mints started to change the composition of the one-cent coin. This change was completed by 1984, hence, the amount of copper in a penny was modified during that period (which was actually because of a change in the price of copper)..
Anyway, we developed a method for dtermining the concentration of a copper(II) ion solution. We put about 50mL of 6 M HNO3 and dropped a post-1983 penny in. We did the same thing for a pre-1983 penny. While waiting for the penny to be completely dissolved, 10 mL cuvettes of 0.0 M (blank DI water), 0.4 M, 0.8 M, 0.12 M, 0.16 M and 0.2 M were made from copper using a Mohr pipet and a volumetric flask. Cuvettes of each of the copper along with cuvettes of both pre- and post-1982 penny solution were made. A computer program was then used to measure the absorbance and transmittance of each solution.
Which brings me to my question, I have the values of all the concentrations and their transmittance and absorbance for each. I have calculated the molarity of the pre-1983 and post-1983 pennies..But I'm not sure how to determine out the mass percentage of copper and zinc in each of the pennies. Anyone know what to do?