This lab shows the students how small molecules are. Molecules of water are so small, that they are able to fit in spaces within the isopropyl alcohol molecules. It also can be used to relate to density. Because the isopropyl alcohol is less dense than the water, it will stack. The volume of the stacked liquids are measured. Then after they are mixed, the volume is measured again. Because the water molecules fill in empty spaces within the alcohol molecules, the volume will decrease.