Percent Copper in Brass—Advanced Inquiry Laboratory Kit

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Big Idea 1, Investigation 2, Primary Learning Objective 1.16. The relative proportions of copper, zinc, and iron in brass influence its properties and uses. How can the percent composition of brass be determined to verify these properties? The purpose of this advanced inquiry lab is to design a procedure to analyze the amount of copper in brass using visible spectroscopy. The lab begins with an introductory activity, in which students measure the absorbance of various metal ion solutions at regular wavelength intervals from 400 nm to 700 nm and investigate the influence of the anion on the absorption spectra. Students identify the correlation among wavelength, absorbance, and concentration for each of three possible ions that may be obtained from brass: copper, zinc, and iron. Once the introductory activity is completed, students design and carry out an experiment to construct a calibration curve and determine the concentration of copper ions in a solution prepared by dissolving brass in nitric acid. Students must investigate the concentration range over which Beer's law is valid and identify the optimum wavelength for analysis. The mass percent of copper in brass is determined from the results of the analysis. Complete for 24 students working in pairs. Perform this experiment in a fume hood or well-ventilated lab.