SIZE OF A GAS MOLECULE
*USING BALLOONS TO COMPARE THE SIZE OF GAS MOLECULES
(Based on a procedure available on the web-- Hyperchemistry on the Web)
Materials: 2 balloons helium
Procedure:
1. Fill an ordinary balloon with helium.
2. Fill a second balloon with air. Keep the circumferences as close as possible.
3. Leave the balloons for 2 days.
Observations:
Anecdotally, record changes in the balloons as 2 days pass (and as more days continue to pass at the discretion of the teacher).
Discussion:
Balloons are solids, but the surface of the balloon ahs irregularly shaped pores and irregular intervals. Helium atoms are less than 1 Angstrom in diameter, where as nitrogen and oxygen, the 2 main gaseous components of air, are approximately 10 Angstroms (1 nanometer) in diameter. Since the pores are not all the same size and since some pores are large enough to let air molecules escape, the balloon cannot be used to quantitatively ascertain the diameters of the atoms (or molecules), but due to the smaller size, helium would be expected to diffuse faster.
Advanced discussion:
Nitrogen (79%) and oxygen (nearly 21%) are the major atoms found in air. They are not , though, found as individual atoms, but rather as diatomic molecules, occurring naturally as paired atoms. Since, diatomic moecules are even larger in diameter than helium atoms, this further explains a difference in diffusion rate through the balloon pores.