5] Membrane and vapor pressure osmometry

Abstract

Osmotic pressure, along with freezing point depression (cryoscopy), boiling point elevation (ebulliometry), vapor pressure lowering, dew point depression, and elasto-osmometry, is one of the colligative properties of solutions. This chapter is concerned with two of these colligative properties: membrane osmometry and vapor pressure osmometry. These techniques are useful for evaluating molecular weights or number average molecular weights and activity coefficients or osmotic pressure second virial coefficients for nonassociating solutes. For associating solutes, these techniques can be used to establish the type of association present, if that is not known beforehand, as well as nonideal terms. Vapor pressure osmometry is most useful for studying lower molecular weight solutes: solutes having molecular weights between 0 and 20,000 (grams/mole). Membrane osmometry, on the other hand, is more useful for the study of larger molecular weight solutes: macromolecules having molecular weights between 10,000 and 1,000,000.