Determination of Sugar Content in Commercial Beverages by Density A Novel Experiment for General Chemistry Courses
Susan K. Henderson, Carol A. Fenn, and John D. Domijan Department of Chemistry, Quinnipiac College, Hamden, CT 06518
A typical experiment performed early in the general chemistry laboratory sequence involves the determination of density. A number ofexperiments based on density determination of rubber stoppers, plastic chips, pennies, and antifreeze–water mixtures have been described (1–6 ). Experiments have also been published in which the density of salt solutions of known concentrations is determined to illustrate the linear relationship between salt concentration and density (7, 8). An alternative to these classical approaches is to use thislinear relationship to ascertain the concentration of a major solute in a liquid sample. In the experiment described in this article, the density of solutions of known sugar concentration is measured and the data are used to determine the sugar content in commercial beverage samples. Students have an avid interest in laboratory investigations of the properties of products they routinely purchase. Theyare often surprised at the results they obtain in this experiment, which indicate the relatively high levels of sugar contained in the beverages they consume on a regular basis. Background The goal of introductory laboratory sessions is to focus on the experimental application of the principles of the topics discussed in lecture and to provide an opportunity for the development of specificlaboratory skills. Introductory experiments that utilize chemicals that are inexpensive and readily available, pose no physical or health hazards, and produce no hazardous wastes are desirable. The experiment described in this article takes into consideration the above factors and has been successfully performed in our general chemistry laboratory courses by approximately 1500 students during the pastfive years. Experimental Details
software, Vernier Software, Portland, OR) or are constructed manually.
Materials This experiment uses granulated 100% cane sugar purchased at a local supermarket and water for the preparation of standard solutions. Commercial beverages with high sugar content, such as fruit juices, iced tea, lemonade, thirstquencher drinks, or carbonated beverages, are used forsample materials. These items are readily available and inexpensive. They pose no chemical exposure hazards and no hazardous wastes are produced. All excess reagents, samples, and wastes from this experiment can be disposed down the drain. Common laboratory glassware, including 10-mL volumetric pipets, and balances with an accuracy of 0.01 g or greater are needed. Graphs are constructed using arelatively simple graphing software package (e.g., Graphical Analysis
Procedure Students prepare about 50 mL each of at least four standard aqueous sugar solutions in the range of 0 to 17 percent by mass sugar. The percent by mass sugar concentration of typical beverage samples will fall within this concentration range. Instructors can have students pool their results if additional data pointsare desired. Specific instructions for standard solution preparation may be provided, or students can be required to independently determine the amounts of sugar and water needed. The actual concentrations of the prepared sugar solutions are calculated on the basis of the weight of sugar and water used to prepare each solution. Care must be taken to ensure that all the sugar is dissolved and thatthe solutions are homogeneous prior to making any density determinations. All solutions and samples should be at room temperature. Three determinations are made of the density of each standard solution. Density values are calculated based on the measurement of the mass of 10.00 mL of each solution delivered by a volumetric pipet. Students are encouraged to practice their pipetting technique until...