How to Determine Osmotic Pressure ?
Osmotic pressure of a given solution can be determined experimentally by several methods. Berkeley and Hartley method is most common method for osmotic pressure determination. The apparatus used for the purpose is often referred to as osmometer.
Berkeley and Hartley Method
Pfeffer's Method
Modern Osmometer
A modern apparatus for the determination of osmotic pressure is shown below in figure.
It consists of a stainless steel cell with a rigid fixed semipermeable membrane. The membrane divides the cell into solute and solvent compartments. A flexible diaphragm is fixed in the solvent compartment. When the solution and the solvent compartments are filled and the taps closed, osmosis occurs. The solvent flows into the solution across the semipermeable membrane. This reduces the pressure in the solvent compartment, causing the diaphragm to distort. Eventually the pressure becomes low enough to stop the occurrence of osmosis. The degree of diaphragm distortion is related to the osmotic pressure of the solution. The diaphragm distortion is measured by a device called strain gauge. The strain gauge provides an electric current that is proportional to the extent of distortion. The gauge is calibrated to give osmotic pressure directly.
Source: Essentials of Physical Chemistry By B.S.Bahl
