Apparatus

One 1 dm beaker
One 5 dm beaker (optional)



Chemicals

The quantities given are for one demonstration

Up to 10 dm of expanded polystyrene packing beads of the type in which glassware is often packed for delivery. A disposable expanded polystyrene coffee cup is also useful.

50 cm of propanone (acetone).

The Demonstration

Pour about 50 cm of propanone into a 1 dm beaker.

Fill the 5 dm beaker with expanded polystyrene packing beads. Add the beads a handful at a time to the propanone. They will shrink and fizz, eventually forming a layer of sticky gel below the propanone.

If the 1 dm beaker is filled with beads, the level will gradually drop as the bottom layer dissolves. The beaker can be refilled at intervals. Over 5 dm of beads will dissolve although this may depend on the type of beads used.

Afterwards the beaker can be passed around the class; but take care as the contents could be difficult to clean off clothes if spilled. The empty 5 dm beaker gives a striking reminder of the volume of beads that has been absorbed.