Diffusion in liquids – Osmosis

CB-IN-56/EV: This test enables to observe how particles move inside a liquid. These movements are due to the diffusion of molecules from a high concentration zone to a low concentration zone. After a certain time a condition of dynamic equilibrium is attained: the concentration of the migration solution has the same value in every zone of the solution. This condition is displayed by the homogeneous colour of the solution. Then sodium chloride is added to increase the density of the solution so that the colorant stratifies on the surface. CB-IN-57/EV: This kit enables to study the osmosis through a membrane. The various molecules cross the membrane with different rates, consequently its permeability is diversified. Small molecules, such as those of water, can cross this type of membrane quickly, whereas the bigger molecules encounter difficulties, for their size, and they are braked. Very big molecules cannot cross the membrane. Also the electric nature of molecules can affect the permeability because non polar molecules can cross more easily, for the nature of membranes. When a selective membrane separates two aqueous environments containing solutes of different concentrations being not able to cross the membrane, water will move to the environment of higher concentration, producing a characteristics osmotic pressure. This quantity is a function of the difference of concentration. The measuring instrument is called osmometer.