- Osmosis - 10 pts.
Diffusion is the movement of molecules from a region in which they are highly concentrated to a region in which they are less concentrated. It depends on the motion of the molecules and continues until the system in which the molecules are found reaches a state of equilibrium, which means that the molecules are randomly distributed throughout the system.

Molecules are in a constant state of motion. If, for example, NaCl (Table salt) is dissolved in water so that the concentration is initially higher in one part of the water than another (order), diffusion will occur so that there is a net movement of NaCl from the area of high concentration to an area of lower concentration (movement toward disorder). If however, the NaCl molecules have a completely even and random distribution throughout the water, then there will be no net movement of NaCl in any direction.

In the experiment on the left, we will examine the effects of concentration on the rate of diffusion. Four holes have been cut into the agar contained in a Petri dish. Into each hole we have placed a dye.

Methylene Blue is a blue dye, KMnO4 Potassium permanganate) is a purple dye. The methylene Blue molecules are about twice as big as the KMnO4 molecules. Move your mouse over the image to see what the petri dish might look like after 20 minutes. The dye molecules have moved from an area where they were highly concentrated (the hole) to an area of lower concentration. They have diffused. The rate of diffusion (size of the "Halo") is different for each hole. Diffusion rates are dependent on the size and concentration of the molecules that are diffusing. It is also dependent on Temperature.

Osmosis