In the Laboratory
Determining the EDTA Content in a Consumer Shower Cleaner An Introductory Chemistry Laboratory Experiment
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Willis Weigand† Department of Chemistry, Pennsylvania State University Altoona College, Altoona, PA 16601-3760;
[email protected] Background Chemistry 11 is an introductory chemistry course offered at The Pennsylvania State University, Altoona College. The main purpose of this course is to provide a foundation for students who have not had chemistry or did not pass the placement exam for the University’s Chemical Principles course, Chem 12. The laboratory component in Chemistry 11 is used to develop the skills required in subsequent chemistry courses. I prefer to utilize experiments that involve consumer products with which students may be familiar to make the laboratories more relevant. One such experiment is a complexometric titration to determine the calcium content in calcium supplements (1). This article describes an experiment in which the student determines the ethylenediaminetetraacetate ion (EDTA) content of a shower cleaner. Chelating agents such as EDTA are an important class of chemical compounds. Not only are they interesting chemically, they are used on a commercial basis in the treatment of heavymetal poisoning and as food preservation ingredients and shampoo additives. Shower-cleaning products have been introduced that are sprayed onto the shower surface and are designed to eliminate the formation of buildup of material on the shower and bath walls. One such product, Tilex Fresh Shower, lists a chelating agent as an ingredient. The Web site for the cleaner confirmed that it contains EDTA along with isopropanol, surfactant, and fragrance (2). Several articles in this Journal and in textbooks provide additional information about chelating agents and complexometric titrations (3–7). Experimental Procedure The experiment is conducted as a guided-inquiry experiment over the course of two laboratory sessions. The students are asked to search various sources, such as textbooks and the Internet, for information about chelants to hand in as a prelaboratory exercise. During the first session, concepts are discussed related to the use of chelating agents along with structure and reactions. The discussions help the students connect the chemistry in the lecture, the laboratory, and the products they use as consumers. The laboratory procedure is developed during the first session with guidance from the instructor. The student’s written procedures are reviewed and †
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additional discussions occur at the start of the second session prior to the titration. For the experiment, the shower cleaner, containing the EDTA, is provided in the original containers. The indicator and buffer solutions are prepared before the experiment by laboratory personnel. The students prepare the standard calcium solution and titration apparatus. The students should conduct at least three titrations, as the wine-red to pale blue endpoint can be a challenge to detect. However, this challenge helps students understand that all chemistry is not as straightforward as the cookbook experiments with which they may be familiar. Results indicate that one cleaner contains about 0.02 M EDTA. No additional laboratory equipment is required beyond the standard titration glassware. Reagents are easily obtained, making the adoption of this experiment straightforward. Hazards The 6 M HCl used to prepare the calcium standard should be prepared and used following standard laboratory procedures. CAUTION: The ammonia buffer solution contains concentrated ammonia; therefore, preparation and addition of the buffer to the titration flask should be conducted in a laboratory hood. W
Supplemental Material
Supplemental material for this article is available in this issue of JCE Online. Literature Cited 1. Hall, J. F. Introductory Chemistry in the Laboratory, 2nd ed; Heath: Lexington, MA, 1996; pp 201–208. 2. Tilex Web site; http://www.tilex.com (accessed Jun 2000). 3. Yappert, M. C.; DuPre, D. B. J. Chem. Educ. 1997, 74, 1422. 4. Novick, S. G. J. Chem. Educ. 1997, 74, 1463. 5. Mossman, D. M.; Kooser, R. G.; Welch, L. J. Chem. Educ. 1996, 73, 82. 6. Wang, T.; Liu, F.; Feng, L. J. Chem. Educ. 1993, 70, 796. 7. Rubinson, J. F.; Rubinson, K. A. Contemporary Chemical Analysis, 1st ed.; Prentice-Hall: Upper Saddle River, NJ, 1998; pp 290–295.
Journal of Chemical Education • Vol. 77 No. 10 October 2000 • JChemEd.chem.wisc.edu
