Winter Fun in a Bottle

Introduction:
Students generate a "snowstorm" scene in a jar while learning about principles of solubility.

Chemical Concepts:

• Solubility
• Saturated solution
• Supersaturated solution

Advanced Preparation:

1. Thoroughly clean and dry a baby food jar
2. Hot glue a toy figurine inside the baby food jar bottom. Use the tongs to hold the figurine by the top. Put some hot glue on the bottom of the figurine and immediately press the figurine on the bottom of the baby food jar. Hold it in place for a few seconds. Allow several minutes for the glue to cool.

Procedure:

1. Carefully heat about 75 mL of tap water in a 250 mL beaker using a hot plate. Do not allow the water to boil.
2. While the water is heating, add approximately 1 gram of solid benzoic acid. Continue to heat and stir the mixture until the benzoic acid is completely dissolved. It will not be necessary to boil the mixture.
3. Carefully remove the beaker from the hotplate and allow the solution to begin cooling.
4. Observe the benzoic acid solution as it begins to cool. Snowy-looking crystals will begin to appear.
5. After the solution is completely cooled to room temperature and the toy figurine is securely glued in the bottom of the jar, stir the snow mixture, and then quickly pour it into the baby food jar.
6. Carefully fill the jar to the brim. If there is not enough of the solution then use tap water. Try to leave as little air as possible in the jar.
7. Cap the jar tightly. You should now be able to turn the winter scene upside down and watch a snowy blizzard fall on your toy figurine.
8. Some electrical tape around the jar lid will seal it more completely and give an added level of security against spilling. If the toy figurine comes loose, it can be repaired by opening the jar, pouring the solution into a disposable cup, regluing the toy figurine, and then replacing the solution. If any solution is lost during the process, replace it with tap water.

Discussion:
A saturated solution contains as much solute as possible at a given temperature and pressure. When the temperature is increased, the solubility increases and more solute dissolves. If the solution is then cooled, the "extra" solute that dissolved with heat will precipitate out. This is occurring when the benzoic acid precipitates out as "snow" in this activity.

Tips:

1. You may use either a 4- or 6-oz baby food jar. Since the seal on baby food jars is not dependably secure, you may wish to purchase 4-oz jars from a local store.
2. It is important to fill the jars to the brim with liquid. Air bubbles tend to cause the benzoic acid to clump at the top.
3. 3. It is more exciting if students bring their own figurines (whatever they find interesting). Solid plastic figurines work the best. You may wish to purchase inexpensive toy figurines at a local store.
4. Allow appropriate time for cooling. Do not try to speed up the cooling process by using cold water or ice. The most beautiful crystals form when the solution is allowed to cool slowly.
5. If the solution is still hot when added to the jar, the figurine will have a greater chance of coming unglued. Don't be impatient with the cooling.

Safety Precautions:
Benzoic acid is slightly toxic by ingestion. Avoid contact with the skin, eyes, clothing, and respiratory track, as it is a severe irritant. Wear chemical splash goggles, chemical resistant gloves, and a chemical resistant apron. Be sure to warn the students not to allow younger family members to take the jar apart or to ingest the solution.

Disposal:
The benzoic acid solution should be neutralized, than flushed down the drain with an excess of tap water. Consult a dependable manual for detailed instructions.

More Teaching Tips from Quantum coming soon!