Separating Cherry Cola
A Simulation

As we have seen in the stories of development of many cancer drugs, many compounds used in medicine come from plant or animal extracts. For example, paclitaxel (Taxol®), an anticancer drug, was extracted from the bark of the Pacific yew tree. The drugs vincristine and vinblastine, both used in treating lymphatic cancer, were first extracted from the Madagascar periwinkle. Living systems, including plants, are complex mixtures containing many substances. The extraction of just one of those substances may require many steps and produce very small quantities of material.

Menu General Safety Guidelines Materials and Apparatus Procedure Extraction Questions Conclusions Observation Sheet

In your classroom you can get an idea of just how these kinds of chemical "extractions" are performed. This lab simulates the extraction of specific compounds from a mixture. The original mixture is a very familiar product—a cherry cola. See how many different components of the cherry cola you can identify in this experiment.

Materials cherry cola lime water ice water

Apparatus 250-ml Erlenmeyer flask* one-hole rubber stopper* right angle bend of glass tubing* 2 ft. rubber tubing (or Tygon®) 100-ml graduated cylinder 125-ml Erlenmeyer flask ("receiving flask") or 150-ml beaker 2 100-ml (or 150-ml) beakers 600-ml or 1000-ml beaker or other container

*A 250-ml sidearm flask can be substituted for the Erlenmeyer flask. If this is the case, you will need a solid rubber stopper to seal the top opening of the flask, and you will not need the bent glass tube.

Procedure

Apparatus set-up (see diagram below.)

1. Assemble the extraction apparatus by carefully placing the bent glass tube into the rubber stopper. Your teacher will show you how to do this safely.

2. Attach the rubber tube to the angle bend.

3. Attach the flask on the ring stand and attach firmly around the neck using the test tube clamp.

4. Place the ring and gauze pad on the ring stand below the flask to help support the flask.

5. Measure out 80 ml of cherry cola and pour it into the flask.

6. Now place the rubber stopper, with its glass tube and rubber tubing, into the Erlenmeyer flask.

7. Obtain ice and prepare an ice bath using the large beaker.

8. Place the small (receiving) flask into the ice bath and insert the open end of the tubing into this flask.

9. Pour about 25 ml of lime water into the remaining small beaker.

Diagram of apparatus set-up.

Extraction

(Note: words/phrases listed in italic print in this section denote observations that need to be recorded on the printable observation sheet.)

1. Light the Bunsen burner and place it under the apparatus.

2. Record your first observations on the data/observations sheet.

3. Observe and record the first “reaction” the cherry cola has to the heat.

4. As the frothing begins, place the tubing into the beaker of lime water and observe the result.

5. Rinse off the outside of the tubing and return the tubing to the small flask in the ice water.

6. Discard the lime water, rinse the beaker thoroughly, and pour in 25 ml of fresh lime water.

7. Continue heating and observe the cherry cola as the fine froth changes into larger bubbles. Observe the changes happening throughout the system—large flask, tube and tubing, and the smaller flask or beaker. Record your observations, especially color and odor.

8. Test the liquid once more by placing the tubing into the lime water briefly. Record your observations; then rinse and return the tubing to the small flask in the ice water.

9. Continue heating vigorously until only about half of the original volume remains in the large flask. This should take from 15–20 minutes. Make final observations of the system.

10. Turn off the burner and allow the apparatus to cool down.

11. Pour the liquid remaining in the large flask into a small beaker. Then pour the liquid from the small receiving flask into the other small beaker.
    1. Compare the beaker of liquid from the receiving flask to the beaker of liquid from the boiling flask. Record your observations.

    2. Now compare the beaker of liquid from the boiling flask to the beaker of original cherry cola that the teacher has kept for you. Record all observations.

12. Wash all your glassware, and clean up all your materials.

Questions

1. What can you infer from the lime water test?

2. Why was the collecting flask placed in an ice bath?

3. Why did the size of the bubbles change so dramatically part way through the extraction?

4. Explain the differences in your observations of the liquid in the boiling flask and the liquid in the receiving flask.

5. Explain the differences in your observations of the liquid in the boiling flask and the beaker of original cherry cola.

6. What do the properties of the distillate (the liquid in the small flask) signify?

7. List the ingredients of the cherry cola. Explain how you know each one is/was present.

Conclusions

1. How does this experiment compare/relate to the work done by chemists in trying to prepare compounds for use in chemotherapy?

For more information, at other Web sites...

The anticancer Agent Collection — color photomicrographs of anticancer drugs, from Florida State University.

Semisynthetic Taxol® (paclitaxel) injection — drug information and history from the Bristol-Myers Squibb Company.

Taxol — scientific overview from the University of Bristol.

Taxol: A Brief Insight — from chemistry student Victoria Farmer, Imperial College of Science, Technology and Medicine.

 

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