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A laboratory demonstration experiment comparing the behavior of starch-based and polystyrene packing peanuts when exposed to water and acetone. Students are asked to predict the outcomes and observe the results. Safety precautions and clean-up procedures are also provided.
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Recommended for Chapter(s): 21
Demo #
Materials NOT in box
Procedure
Safety
Clean Up
Stockroom Notes
Discussion
The molecular structure of polystyrene is seen below.
Since polystyrene only contains carbon hydrogen bonds, it is nonpolar and will only dissolve in nonpolar solvents, because like dissolves like.
The general structure of starches is seen below.
Starch contains oxygen carbon and oxygen hydrogen bonds, making it a polar molecule. This will only dissolve in polar solvents.
The two solvent used in this demo are water and acetone (seen below).
Water Acetone
While both water and acetone are polar molecules, acetone is only slightly polar (only contains dipole-dipole forces and London forces while water contains H-bonding, dipole- dipole forces, and London forces) and can dissolve non polar substances. This is why the non-polar polystyrene dissolves in acetone but not water and the polar starch molecules dissolve in water but not acetone.
After the demo is done the polystyrene will be in the bottom of the beaker. This can be used to point out that the packing peanuts are made mostly air with only a little polymer which is seen in the bottom of the flask.