Osmotic phenomena, applications

One can also recognize that application of sufficient pressure (above the equilibrium osmotic pressure n) to the right-hand chamber in (7.67) must cause the solvent flow to reverse, resulting in extrusion of pure solvent from solution. This is the phenomenon of reverse osmosis, an important industrial process for water desalination. Reverse osmosis is also used for other purification processes, such as removal of H20 from ethanol beyond the azeotropic limit of distillation (Section 7.3.4). Reverse osmosis also finds numerous applications in wastewater treatment, solvent recovery, and pollution control processes. 

The general conclusion which has been come to, however, is that the Neinst method of treatment of e m f in cells represents a great advance m our knowledge of this important phenomenon One or two simple cases of the application of the osmotic theory will now be given... 

The osmotic pressure phenomenon manifests itself in many interesting applications. To study the contents of red blood cells, which are protected from the external environment by a semipermeable membrane, biochemists use a technique called hemolysis. The red blood cells are placed in a hypotonic solution. Because the hypotonic solution is less concentrated than the interior of the cell, water moves into the cells, as shown in Figure 12.14(b). The cells swell and eventually burst, releasing hemoglobin and other molecules. 

Osmosis is a phenomenon of great importance in many applications and particularly so in polymer science. It is a very accurate and sensitive method of determining M and provides a useful application of the theories of solution thermodynamics developed in Section 3.1. The apparatus used for measuring osmotic pressure is shown schematically in Fig. 3.9. It consists essentially of a chamber with two compartments separated by a semi-permeable membrane. In one compartment there is pure solvent and in the other there is a polymer solution and both are at the same temperature. The membrane is permeable only to solvent molecules and is not permeable to polymer molecules. If both of the compartments are at the same pressure initially it is found that solvent molecules tend to diffuse from the pure solvent through the membrane and the diffusion stops only when the pressure in the solution compartment is increased by either applying an external pressure or allowing a pressure head to develop. The pressure which is required to stop solvent diffusion across the membrane is called the osmotic pressure. 

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