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DISTILLATION OF WATER FROM AN AQUEOUS SOLUTION USING A DISPOSABLE APPARATUS

* PURPOSE


Using readily available materials, students separate a colorless liquid from a common colored solution by distillation.

* DESCRIPTION

This experiment is particularly appropriate for middle school science classes or for a general or first-year course where scientific glassware is unavailable. A simple distillation is performed using a soda can and aluminum foil in place of traditional glassware. The experiment works sufficiently well to enable students to obtain a colorless liquid from a colored solution. Not only is the equipment inexpensive and readily available, but the entire apparatus is disposable.

* TIME REQUIRED

One lab period.

* MATERIALS

Chemicals:
crushed ice solution to be distilled--cranberry or apple juice, coke, orange soda, or colored aqueous solution
Equipment:
empty soda can--Pepsi, 7-Up, etc.
4 to 8-oz clear glass jar with narrow opening at top larger jar or other container to hold jar above 4-In x 12-in piece of aluminum foil
Bunsen or alcohol burner
ring stand
iron rings wire screen
*See Modifications / Substitutions

* HAZARDS

If alcohol burners are used, they should be filled when cold, only by the teacher. Adding common salt to the burner fuel makes it easier for students to see the flame and thus avoid possible burns. The aluminum foil condenser becomes quite hot during the distillation. Care should be taken to avoid touching it during collection of the distillate. Goggles must be worn throughout the experiment.

* MODIFICATIONS/SUBSTITUTIONS

  1. A wide variety of common household solutions can be distilled in this experiment, including fruit juices and strongly colored sodas.
  2. Highly colored inorganic chemical solutions (KMnO4, K2Cr2O7, CuSO4, etc.) should be avoided because they will react with the aluminum in the cans.

* PROCEDURE

  1. Rinse the soda can clean.
  2. Add the solution to be distilled until the can is l/3 to l/2 full. Boiling chips may be added if available, but are by no means necessary.
  3. Mount the soda can above the burner on a wire screen supported by an iron ring (attached to the ring stand). Mount the second iron ring around and near the top of the can to prevent it from tipping over.
  4. Insert the smaller glass jar into the larger one and surround liberally with an Ice-rich slush bath.
  5. Prepare an air-cooled condenser made of aluminum foil. This is best done by wrapping the foil lengthwise around a dowel rod or broom handle, taking care to seal the seam that runs the length of the foil tube by making several folds of foil neatly pressed back on itself. (Failure to do this will result in. poor efficiency during distillation.)
  6. Fit one end of the condenser into the opening at the top of the soda can. Gently bend the other end down and Insert it into the smaller glass jar which serves as a receiver flask for the distillation.
  7. Heat the soda can and its contents with a steady flame. As the solution boils, some vapor can be seen escaping from around the mouth of the can. Still, enough vapor makes its way through the air-cooled condenser so that condensation soon occurs In the chilled receiver flask.

* DISPOSAL

After pouring the mother liquor down the drain, the entire distillation apparatus may be disposed of with the solid waste. If desired, the jars may be saved for re-use. The aluminum cans could be recycled.

* DISCUSSION

Review the processes of evaporation and condensation with students. Emphasize the principles which allow distillation to be used as an effective purification tool (i.e., contaminants must be non-volatile). Be sure to compare the color of the starting material with that of the distillate.

* TIP

For better sealing of the condenser tube, use one of the following procedures. The aluminum foil at the mouth of the can may be sealed with masking tape. Alternately, the condenser tube can be fitted carefully Into corks or stoppers at the mouths of the can and the collection bottle; however, the system should not be completely sealed.

* REFERENCES

Holtzclaw, H.F., Jr., Robinson, W.R., and Nebergall, W.R., College Chemistry with Qualitative Analysis, D.C. Heath and Company, Lexington, MA, 1984, p. 285.
This work describes the theory of distillation. A similar discussion could be found in any college-level chemistry text.

Submitted by Stephen Cotton, Jean Crowley, Joan D'Agostino, Dan Holmquist, and John Hnatow

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