Physical and chemical properties!

What we can do!

Substances tend to dissolve in things that are similar to them. By ‘similar’ in this case we mean in terms of their polarity. Some stains dissolve better in a polar substance like water and some stains require a more non-polar substance to dissolve them away.

Place two large glass beakers side-by-side. Pour water into the first beaker until it’s about half full. Place a Styrofoam cup in the water beaker. Nothing will happen. Styrofoam is non-polar, water is polar and, since “like dissolves like”, they will not dissolve in each other.

The goo you retrieve from the beaker is actually polystyrene plastic (#6 in recycling code) and is the same plastic used to make plastic table ware, etc. You can shape it any way you wish while it is wet and it will harden over time as all the acetone completely evaporates away. In order to completely dissolve the plastic, you’d need a stronger and more non-polar solvent.

Now pour some acetone into the other beaker and place another Styrofoam cup into that beaker. You’ll see the cup slowly break down until it is just a glob of goo. Acetone can get in between the components of the polymer of plastic and allow the air in the cup to escape (don’t worry, they don’t use CFC’s in Styrofoam anymore so there is no harm to the environment when doing this demo).

Place starch packing peanuts (the environmentally friendly packing option commonly used today) in a beaker of acetone. Since the starch packing peanuts are polar, they will not dissolve in acetone. Put the starch packing peanuts in a beaker of water, mix around a bit and you’ll see they dissolve readily.

Old-fashioned Styrofoam packing peanuts are fun to play with too. You’ll need a large beaker filled about half full with acetone. Have someone ready with a large wooden spoon and start loading the Styrofoam packing peanuts into the beaker as your helper stirs like crazy. You’ll be amazed at how many peanuts will fit into the beaker.