Lab Report

Topics: Chemistry, Spectroscopy, Ammonia Pages: 2 (511 words) Published: September 24, 2012
This lab report will be detailing the steps taken and the results discovered when using spectrophotometry to determine the percentage of copper in a copper-clad penny and the thicknes of the copper layer on the copper-clad penny. After 1982, copper coating has been used in the creation of the penny because the cost of pure copper has increase to the point that the amount needed t omake a penny cost far more than the actual value of the penny. This lab allowed us to see just how much copper coating was used in a particular penny. Not knowing the about information, my original hypothesis was that the penny would contain a great deal of pure copper. The following report will walk you through my actual findings.

Our lab consisted of three parts: determining the proper wavelength for the spectrophotometer, constructing a calibration curve for Cu(NH3)42+, and finally determining the actual content of copper in a penny. IN the first step of the lab, we used water to calibrate our spectrophotometer, and then measured the absorbance of Cu(NH3)42+ at different wavelengths, in order to determine the optimal one. In our group, we determined 600nm was the optimat wavelength with an absorption of 1.32. The chart below shows our absorption rates:

We then went on to part two, where we used the optimal wavelength to determine a calibration curve for the absorbance of Cu(NH3)42+. We took varying levels of a Cu2+ solution and added it to ammonia an looked at the absorbance amounts, which are seen in the below graph:

With parts one and two of our lab complete, we now know the optimal wavelength to measure absorption at and we have determined absorption levels of Cu(NH3)42+. Being that we followed the Beer-Lambert Law that concentration and absorbtion are related, we were able to look at the absorbance levels of light through Cu(NH3)42+, and now in part three determine the amount of copper a given penny may contain. We collected data from a 2005 penny in our group. IN...
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