General chemistry students at the University of North Georgia perform an experiment in which copper is precipitated from copper (II) chloride dihydrate solutions, through the addition of magnesium turnings, in order to calculate the percent composition of copper in the compound. Students allow the reaction to continue until it is apparent, based on the color of solution, that all of the copper was precipitated from solution. When the solution is colorless, students assume no more copper is left in solution. Afterwards, excess magnesium is reacted with hydrochloric acid and the solution is filtered to separate the copper. From previous studies on this experiment, it has been shown that a colorless solution is not necessarily indicative of full precipitation. In this study, a spectronic 20 was utilized to determine the concentration of copper (II) chloride left in student filtrates after the removal of copper. Samples were collected from multiple lab sections. The amount of magnesium added by the students varied across different lab sections. A calibration curve was used to calculate the concentration of copper remaining in the filtrates from the measured absorbance values. The average concentration of copper left in the student solutions was .00789 M.

Analysis of general chemistry student samples for concentration of copper in a percent composition laboratory experiment

2019 Spring National Meeting

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