Comparative Studies between Different Aqueous Electrolytes

Isopiestic Method.— The isopiestic method can be used to determine provided only one of the components is volatile. The unknown solution and reference solution containing the same volatile component but different involatile components are placed in dishes on a metal block in an airtight enclosure. The volatile component distils between the two solutions until their compositions are such that they have the same chemical potential of volatile component. After equilibration the two solutions are analysed. As the isopiestic method is a comparative method it is necessary to know the variation of vapour pressure with composition for the reference solution. The technique has the advantage that no pressure measurements are required. The method has been frequently used in the study of electrolytes and involatile non-electrolytes in aqueous solutions. Corneliussen et a/. have used the method to study polymer solutions. An apparatus suitable for measurements with organic mixtures has been described by Harris and Dunlop. The method is suitable only when there is no possibility of distillation between the involatile component in the reference solution and the involatile component in the unknown solution. 

---