Demonstrate Diffusion

If you are a science teacher and need to demonstrate diffusion this is a great activity for you. You will need a small bar of soap like from a hotel (not the kind that float), a 1 quart glass jar with a lid, glue paper, pencil, and water.

The tiny bars of soap from hotels or airplanes are excellent for this experiment, but if you don't have any, slice a piece of regular soap into several chunks that will cover the bottom of the glass jar.

Glue a strip of paper up the side of the jar. You will use this strip of paper to make marks on to collect your data. Drop the woap into the jar, covering the bottom, and fill the jar completely with water. Screw the lid onto the jar and set the experiment in a quiet plae where it will not be diesturbed. Check the experiment every week for several weeks. You will see two layers in the jar. The soap dissolves to form a heavy solution underneath the water. Mark the soap position on the paper each week. This layer slowly creeps upward. Do you know why?

What happens? At first, the soap dissolves in the water surrounding it. This is why you see the layer of soap solution at the bottom. However, the molecules of a asubstance are always in motion, even though the substance may appear to be sitting quietly. The soap and water molecules are in constant motion, always interacting. Eventually, the sop solution distributes itself throughout the entire jar of water. The scientific name for this process is diffusion.