osmosis

Osmosis: Spontaneous flow of solvent molecules through a semipermeable membrane from a pure solvent to the solution (or from a dilute solution to a concentrated solution) is termed as osmosis. Osmotic Pressure (): The hydrostatic pressure built up on the solution which just stops osmosis. Alternatively, it may be defined as the pressure which must be applied to the concentrated solution in order to stop osmosis. For dilute solutions  = CRT = hg Where C is the total molar concentration of all the free species present in the solution, h is the height developed by the column of the concentrated solution and  is the density of the solution in the column. On the basis of osmotic pressure, the solutions can be classified in three classes. Isotonic solutions: Two solutions having same osmotic pressures at same temperature. (This implies C1 = C2). Hypertonic and Hypotonic Solution: When two solutions are being compared, then the solution with higher osmotic pressure is termed as hypertonic. The solution with lower osmotic pressure is termed as hypotonic. Important: Osmotic pressures can be determined quite accurately, hence it is used in the determination molecular weights of large proteins and similar substances. Reverse Osmosis: If a pressure greater than the osmotic pressure is applied on the concentrated solution, the solvent starts to flow from concentrated solution to dilute solution (or pure solvent). This is reverse osmosis. One of its chief uses is desalination of sea water to get pure drinking water.