Vapor pressure osmometry
Encyclopedia
Vapor pressure osmometry is a technique to measure the number average molecular weight of a polymer. It is based upon Raoult's law that governs change in vapor pressure
of a solution based on the mole fraction of the solute.
The vapor pressure osmometer is composed of two chambers: one for pure solvent and the other to contain solution, where the solute is the polymer whose molecular weight is unknown. Thermistors in each chamber provide an electrical signal (the actual measurement) of differential heating to achieve a vapor equilibrium in each chamber.
By measuring solutions of different concentrations of solute with a known molecular weight standard, a plot of concentration versus electrical differential can be prepared. Similarly, the unknown is then prepared and measured with the number average molecular weight derived from the standard plot.
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
of a solution based on the mole fraction of the solute.
The vapor pressure osmometer is composed of two chambers: one for pure solvent and the other to contain solution, where the solute is the polymer whose molecular weight is unknown. Thermistors in each chamber provide an electrical signal (the actual measurement) of differential heating to achieve a vapor equilibrium in each chamber.
By measuring solutions of different concentrations of solute with a known molecular weight standard, a plot of concentration versus electrical differential can be prepared. Similarly, the unknown is then prepared and measured with the number average molecular weight derived from the standard plot.