Separating Cherry Cola
A Simulation

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General Safety Guidelines Teacher Notes Conducting the Activity Advanced Preparation Completed Observations Sheet Questions Conclusions

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In many of the biographical readings in Pharmaceutical Achievers the story relates the discovery of a new cancer drug. Often, the chemical that is the active ingredient in the new drug existed in a plant or other naturally occuring organism. Taxol^® in the Pacific yew tree and vinblastine in the Madagascar periwinkle are just two examples. In many cases, the natural product is later modified in the laboratory, but before that can happen, the natural substance must be isolated from its plant source. This lab is included to acquaint students with often-used methods of separation in chemistry.

In the lab, a sample of cherry-flavored cola is tested for the presence of carbon dioxide and then heated. As a result of the heating, the compound that gives the cola its distinctive odor is evaporated off. Water, which makes up most of the mixture, is also boiled off, but this component is condensed and recovered. Four components--carbon dioxide, water, coloring agent and the substance responsible for the cherry odor--can be identified.

Teacher Notes

1. This experiment is offered as a simulation of the process of extracting specific compounds from plant or animal resources. Although it is actually a distillation experiment the students are doing, the focus in this lab is on the variety of substances separated from the original mixture, rather than the purification of those substances. Mention can be made, however, that this process not only separates the components, but also purifies them, although several repetitions of the process would be necessary for actual purification.

2. For further information on extraction methods, consult SourceBook Version 2.1 (Orna, Mary Virginia, Schreck, James O., and Heikkinen, Henry, editors. New Rochelle, NY: ChemSource, 1998. See chapter "Separations," Volume 4.)

3. The lab activity can be completed in one 45-minute period.

4. The actual amount of soda in the original flask is unimportant. The volume of 80 ml was chosen simply because a 12-oz. can holds 355 ml, so that four student lab groups can be satisfied with one can of soda, leaving enough for a 35-ml sample for comparisons at the end of the experiment.

5. A sidearm flask simplifies the apparatus, but availability may be a problem.

6. The procedure denotes in bold print the specific items that need to be recorded on the observation sheet. The bold notes correspond to the appropriate place to put observations on the data sheet.