Diffusion and osmosis

The diffusion phenomenon can occur in liquids or gases due to the displacement of molecules from an area with high concentration to an area with low concentration. The movement of a solute through a selective membrane is called dialysis. This kit includes a dialysis tube to show the selective diffusion of molecules. The size of membrane pores determines which substances can cross the membrane. In this case, students can observe the passage (inside the tube) of the small iodine molecules which form a complex of deep colour binding to starch. The big size of starch macromolecules prevents them from crossing the membrane. Through this kit, it is possible to observe diffusion through selective membranes and visualize the effects of osmotic pressure.