In Chemical Mystery #12, curious floating and sinking behavior is exhibited by three different balloons. To pull off this experimental trick, a tank is filled with sulfur hexafluoride (SF6), and three balloons are filled with three different gases: helium, exhaled breath, and SF6. The balloon filled with SF6 sinks when placed in the tank. The balloon filled with exhaled breath floats in the tank, and the helium filled balloon floats up out of the tank and through the air.
Bob Worley and Amiee Modic commented on this experiment, noting that many teachers do not have access to SF6 and therefore would likely be unable to conduct this experiment in their classrooms. This gave me the idea of trying to figure out how to pull off the trick using easily obtained items. I have experimented a little bit and found that it is easy to pull off this experimental effect using baking soda, vinegar, a large deep plastic bin, balloons, and a tank of helium (which can be purchased in the party section of stores such as Wal Mart). It is important to note that this experiment works best when using balloons with very thin plastic skins when inflated. Water balloons work well.
First, baking soda and vinegar are mixed in the plastic bin to fill the container with CO2 gas:
NaHCO3 + HC2H3O2 --> NaC2H3O2 + H2O + CO2
One balloon is filled with helium, a second balloon with exhaled breath, and a third balloon with half exhaled breath and half helium. Some experimenting may be required to get the right density of the balloon filled with helium/exhaled breath. The balloons display different floating and sinking behavior when placed into the tub filled with CO2 - quite similar to the experiment done with SF6:
Amiee and Bob, thank you for commenting on Chemical Mystery #12 and noting that many teachers do not have access to SF6. Your comments provided me with inspiration to get into the lab to try some further experimentation, which I always enjoy having the chance to do!
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Extension to baffling balloons
A nice extension to this would be to have the students blow soap bubbles into the tank filled with CO2. They can then more easily observe the rainbow effect on the skin of the bubbles leading to a discussion of electromagnetic spectrum, reflectance and diffraction, etc. Often the bubbles will stick together and start to form linear, trigonal planar, etc arrangements that can compliment discussions of structures.
VSEPR and bubbles. Who would have thought?
Great ideas, David. I am familiar with the experiment wherein bubbles are blown into a container of CO2. However, when doing this experiment it never occurred to me to observe the rainbow patterns on the bubbles. I'll soon be heating into the lab to blow bubbles into a tank of CO2 to look for the various VSEPR shapes! Thank you for sharing these ideas!
Very interesting experiment
Very interesting experiment. I showed your video in my university and we also conducted this experiment. Unfortunately, I did not shoot it on video, but it turned out almost the same as on your video. It was very informative and interesting for all students. After the experiment, all students were given the task to write an argumentative essay about this experiment.