Question

I did two wavelength vs absorbance graphs. one for copper and one for brass in my chem lab. I plotted them. The copper had a lambda max of about 680 nm. The brass at 380 nm. At middle wavelengths the two were about the same. The copper started to increase in absorbance over the brass at about 580 nm. By looking at this info why can I say that brass has other elements besides copper in it?

Answer 1

When studying absobance, an important law to be kept in mind is the Beer Lambert's law. It states that the absorbance of any sample of a substance is directly proportional to the concentration of the substance in the sample and epsilon value of the sample. Brass is an alloy of copper and zinc and the lambda max obtained for brass will depend on the concentration of copper in brass as well as concentration of zinc and their epsilon values. It brass were just copper, then lambda max would had been 680 nm. However, due to presence of zinc, the lambda max changes its value and depending on the exact concentration and epsilon. Therefore, it can be inferred that brass has other elements than copper.