Botanical Balloons
Different extracts placed in balloons make scientific inquiry fun.

Concepts
diffusion, particulate nature of matter, volatility

Materials
  • dropper
  • marking pen
  • rubber balloons
  • different flavoring extracts such as vanilla, peppermint, orange, etc.

Getting Ready
Put different numbers on each of the extract containers.

Procedure
1. Give each group a rubber balloon, a dropper, and a flavoring extract
2. Have the students write the number of their extract on their balloon.
3. Instruct each group to put 2 drops of extract into their balloon by inserting a dropper as far as possible in to the balloon. This way the extract does not get on the neck of the balloon.
4. Have each group blow up the balloon, tie it off, and shake it a few times.
5. Have groups pass the balloons around, smell them and record the odors they detect.
6. After all the groups are finished making observations, have each grouptell what was actually used in their balloon.

Explanation
To understand why we can smell an extract through a balloon three important factors must be considered: the volatility of the particles responsible for odors, the permeability of balloons to gaseous particles, and the solubility of one chemical in another. Flavoring extracts are usually a mixture of substances extracted from a plant using alcohol or water. The molecules that are responsible for the odor of the extract are usually fairly volatile, which means they easily evaporate from the liquid to the gaseous state.

The rate at which gas particles diffuse is related to molecular mass. The molecules of extract are considerably larger and more massive than oxygen or nitrogen. Looking simply at this principle, normal air should diffuse much quicker than the extracts. Since air in a normal balloon does not diffuse quickly, one can assume that diffusion for the extracts should take an extremely long time. This is not the case, however, as vanilla extract is detectable almost immediately. There must be another factor involved in the movement of the odor molecules through the balloon walls. Perhaps the molecules of extract actually interact with or dissolve in the latex layer of the balloon (like dissolves like). Molecules of the extract could dissolve through the latex to the outside of the balloon and then diffuse through the air to reach our noses.


figure12.jpg
Figure 12: Vanilla extract placed in a balloon can be smelled outside the balloon.


*Adapted from “Smelly Balloons”, Teaching Chemistry with TOYS, pp. 183-188

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