ION-PAIRING AND RELATED TOPICS

The Bjerrum theory of ion pairing may be regarded as an approximation method for calculating the thermodynamic properties of the restricted primitive model (essentially charged hard spheres in a dielectric medium for an electrolyte solution. For this model, with parameters appropriate to a 2–2 electrolyte in water or a 1–1 electrolyte in ethanol, the structural implications of Bjerrum's theory are compared with the structural information in the ion-ion pair correlation functions g+_(r) and g++(r) obtained in a new series of hypernetted chain equation (HNC) calculations for the same model. The degree of ion pairing implied by Bjerrum's theory is rather similar to the comparable functional of 9+->rl, although there are percentage differences even at concentrations as low as lmM. The 9++(r) results are interpreted as showing that triple ions make a streng contribution to the solution properties even at conoentrations as low as lOmM. The implications of these results for the interpretation of data for the electrical oonductivity of electrolyte solutions and of data for the concentration dependence of electron exchange reactions such as Fe2+ + Fe3+ = exchange are briefly discussed. © IUPAC