An ultra - violet spectrophotometric study of the ion association of cupric sulphate in methanol - water mixtures

Abstract

The ions of an electrolyte solution are subject both to long range coulombic forces and short range local inter-actions. In the 1920's Debye, Hűckel & Onsager suggested formulae to account for the long range coulombic interactions. These formulae, in spite of their approximations, gave a good account of the behaviour of many dilute aqueous electrolyte solutions. However, they were less successful with non-aqueous solutions and solutions involving ions of charge greater than unity. When ions approach one another closely, the coulombic interaction between them is high and the approximations of simple theory can no longer hold. It is possible to avoid these difficulties by employing a method developed by N. Bjerrum, C.W. Davies, Kraus, Fuoss and others. This involves treating those pairs of oppositely charged ions which are within a certain distance of one another as a separate species in thermodynamic equilibrium with the free ions.