Diffusion and Osmosis
Just as a gas can diffuse into vacant space or another gas, a solute can diffuse from a solution into the pure solvent.
If you pour a saturated aqueous solution of potassium permanganate with the help of thistle funnel into a breaker containing water.it forms a separate layer at the bottom. After some time, you will see the permanganate actually diffusing up into water. This continues until a homogeneous solution is obtained.
The diffusion of solute into solvent is, in fact, a bilateral process. It consists of: (1) the solute molecules moving up into solvent; and (2). The solvent molecules moving down into solution.
This intermingling of solute and solvent molecules goes on so that ultimately a solution of uniform concentration results.
It is the tendency to equalize concentration in all parts of the solution which is responsible for the diffusion of the solute.
This diffusion of solute will also take place when two solutions of unequal concentration are in contact. Solvent and solute molecules will pass from the dilute to the concentration solution and solute molecules will pass from the concentrated to the dilute solution until equality of concentration is achieved.
What is Osmosis?
Let us consider a pure solvent and solution separated by a membrane which permits the passage to solvent molecules but not to solute molecules. Only the solvent will diffuse through the membrane into solution. A membrane which is permeable to solvent and solvent and not to solute, is called a semipermeable membrane.
The flow of the solvent through a semipermeable membreane from pure solvent to solution or from dilute solution to concentrated solution, is termed Osmosis (Freak Osmos=to puch).
It must be clearly understood the diffusion of solvent molecules through a semipermeable membreane is taking place in both directions. That is, solvent molecules are passing from solvent to solution, and also from solution to solvent, But since the diffusion from solvent to solution or from dilute to concentrated solution, is more rapid, the net flow of the solvent is from low to high concentration.
The phenomenon of osmosis can be demonstrated by fastening ba piece of animal bladder or cellophane over a funnel . An aqueous Salt 🧂 solution is place through the semipermeable membrane from water 💦 to the salt solution. The flow of water into the funnel shows up as the solution is seen rising in the tube remarkably.
Some interesting experiments demonstrating osmosis
Many natural membranes are semipermeable e.g., pug's bladder, skin around white of an egg 🥚, membrane around the red blood corpuscle, and the membrane in the cell of the plant ☘️. Some interesting experiments demonstrating osmosis.
(1). Silica Garden
Crystals of many salts e.g., ferrous sulfate, nickel choroide, cobalt nitrate and ferric chloride are placed in a solution of glass material (sodium silicate). The layers of matalic silicatals formed on the surface of crystals by double decomposition are semipermeable. The water from outside enters through these membrane which burst and form what we call a Silica Garden.
(2). The Egg Experiment
The outer hard shell of two eggs of the same size is removed by dissolving in dilute hydrochloric acid. One of these is placed in distilled water 💦 and the other in saturated salt 🧂 solution shrinks. In the first case, water diffuse through the skin (a semipermeable membrane) into the egg material which swells. In the second case, the concentration of the salt solution being higher than the egg material, the egg strinks.
