In the Classroom edited by
Erica K. Jacobsen Journal of Chemical Education
JCE Classroom Activity #105. A Sticky Situation: Chewing Gum and Solubility lez,* Jose A. Cintron-Maldonado, Ilia E. Pe rez-Medina, Ingrid Montes-Gonza nica Montes-Berríos, and Saurie N. Roma n-Lo pez Vero Department of Chemistry, University of Puerto Rico-Río Piedras Campus, San Juan, Puerto Rico 00931 *
[email protected] Instructor Information Solubility is an important process, and educators are always seeking new ways to help their students understand it (1-4). In this Activity, students investigate the solubility of a chewing gum first when it mixes with saliva and then when they add chocolate to the blend. Based on their observations of several solubility tests, students explain what dissolves the sugar, the artificial flavorings, and the gum base present in the chewing gum using terms such as solubility, “like dissolves like,” and polar and nonpolar. Background Intermolecular forces are one of the factors responsible for the solubility of one substance (the solute) in another substance (the solvent). When the solute and solvent have similar types of intermolecular forces, the solute dissolves in the solvent and a homogeneous mixture is formed. For example, sugar (sucrose, C12H22O11) and water are polar compounds. Sugar will dissolve in water because both molecules have permanent dipole moments that interact strongly when the substances are mixed. A nonpolar molecule does not have a permanent dipole moment, and the intermolecular interactions are typically weak (London dispersion forces). When oil, a predominantly nonpolar compound, is mixed with water the substances are not miscible. To help students understand this concept, instructors often use the phrase “like dissolves like”. Chewing gums are typically composed of sugar, flavorings, softeners, and a gum base (e.g., polyethylene, a nonpolar polymer). Saliva is a polar mixture composed of about 98% water, electrolytes, mucus, antibacterial compounds, and enzymes. When a person chews a piece of sugar-coated gum, the saliva dissolves any hard-shell sugar coating and artificial flavorings present in the gum, but not the gum base itself (5-7). A nonpolar solvent would be capable of dissolving a nonpolar polymer gum base. Chocolate is a natural food that contains cocoa butter, a fat, as the main ingredient (8, 9). Although fat molecules have a polar region, their long hydrocarbon chains make the nonpolar intermolecular forces (London dispersions) prevail. For this reason, the cocoa butter present in chocolate and the gum-base polymer of chewing gum are soluble in each other. Integrating the Activity into Your Curriculum Several chemical concepts related to solubility can be reviewed or taught through this Activity: “like dissolves like”, intermolecular forces, solute, solvent, polar compound, nonpolar 396
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compound, solubility, and even aqueous phase and organic phase when explaining the process of dissolving the sugar coating and the artificial flavorings from the gum as an extraction. In addition, the Activity provides the opportunity to introduce organic compounds and their chemical structures (10, 11). Previous JCE Featured Molecules columns have included structures of substances found in candy and chocolate (12). About the Activity Students first perform several solubility tests: sugar in water, oil in water, and sugar in oil. They relate observations from these tests to solubility tests performed with Chiclets, a gum with a hard-shell candy coating: gum in water, gum base in oil. To finish, they chew a piece of gum, then observe what happens when they chew the gum together with chocolate. For safety concerns, perform this Activity in a nonlaboratory environment. Students should not swallow the mixture of chocolate and chewing gum. Alternatively, students can do the procedure without chewing the gum. A spoon in a dish or mortar and pestle could be used to “chew” the gum. This eliminates any risk of students swallowing the gum-chocolate mixture and concerns about disposing of chewed material in a sanitary manner. All the materials used for this Activity should be properly disposed of according to local regulations. Typically, the watersoluble solutions may be washed down the drain with large amounts of water; oil can possibly be collected in sealed containers and placed in the trash. Students should wash their hands before and after completing the Activity. Literature Cited Kjonaas, R. A. J. Chem. Educ. 1984, 61, 765. Blake, B. J. Chem. Educ. 2003, 80, 1348–1350. Tomkins, R. P. T. J. Chem. Educ. 2008, 85, 310–316. Alger, D. B. J. Chem. Educ. 1994, 71, 281. What Is in Chewing Gum from About.com: Chemistry. http:// chemistry.about.com/od/chemistryfaqs/f/chewinggum.htm (accessed Jan 2010). 6. Gum Base from Gum Base, Co. http://www.gumbase.com/ on-line/Home/Confectionery/Products/GUMBASE.html (accessed Jan 2010). 7. M. Hebrank. How Much Sugar Is in Bubble Gum? http://www. ciblearning.org/pdf/Exercise.HowMuchSugarIsInBubbleGum.pdf (accessed Jan 2010). 8. What's That Stuff?: Chocolate. http://pubs.acs.org/cen/whatstuff/ stuff/7849sci5.html (accessed Jan 2010).
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Vol. 87 No. 4 April 2010 pubs.acs.org/jchemeduc r 2010 American Chemical Society and Division of Chemical Education, Inc. 10.1021/ed800135j Published on Web 03/09/2010
In the Classroom
9. Flexible Chocolate. http://www.rsc.org/delivery/_ArticleLinking/ DisplayHTMLArticleforfree.cfm?JournalCode=SM&Year=2006& ManuscriptID=b518021j&Iss=4 (accessed Jan 2010). 10. Theobromine Chemistry from About.com: Chemistry. http:// chemistry.about.com/library/weekly/aa090301a.htm (accessed Jan 2010).
r 2010 American Chemical Society and Division of Chemical Education, Inc.
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11. Tannenbaum, G. J. Chem. Educ. 2004, 81, 1131–1135. 12. Coleman, W. F. J. Chem. Educ. 2007, 84, 621; 2004, 81, 1232.
Supporting Information Available Student activity worksheet; answers to student questions; student data table. This material is available via the Internet at http://pubs.acs.org.
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