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In this General Chemistry laboratory experiment, students perform a simple procedure that is designed to introduce them to basic laboratory techniques, statistical analysis and the concept of green chemistry. It is typically performed during the first or second week of the school year when students have minimal chemical knowledge. The goal is not so much to have them do an analysis of the chemical reaction but rather to provide them with early hands-on laboratory experience and increase their awareness of chemical waste. If done later in the term, instructors might wish to supplement the post-lab analysis by incorporating redox and stoichiometry concepts.
The procedure for this experiment is straightforward. Galvanized nails are placed into 6M hydrochloric acid to dissolve the zinc galvanization. By weighing before and after, students determine the mass of zinc used to coat the nail and determine if it complies with industry standards for galvanization. This process is repeated with four more nails and students perform a basic spreadsheet analysis of their results. In addition, they add their data to a class data set to determine how their confidence in the results changes when more data are available to analyze. When finished with the procedure, students are asked to consider the waste that they produced and process it by adding sodium hydroxide to neutralize the excess acid and precipitate zinc hydroxide. In so doing, the total volume of waste is reduced. Waste is collected in glass “sedimentation stations” and at the end of the week, the aqueous layer is considered to be safe enough to go down the drain.
While waste processing is not an inherent component of the green chemistry movement, consideration of the waste that is produced is the first step in assessment of a procedure for waste prevention and less hazardous design. Because this experiment comes so early in the year, it serves as a stepping-stone for later conversations on greener processes that are implemented in the curriculum. As a post-lab activity, students are asked to research alternative uses of zinc hydroxide that could be employed to utilize the laboratory waste.
Summary prepared March 2012 by Dr. Deborah Exton, University of Oregon.
Exton, D. General Chemistry in the Laboratory, 2/e, McGraw-Hill Learning Solutions, ISBN 0-07-804433-5., Print