Partial molal volumes of ions

Abstract

Partial molal ionic volumes have been calculated using the equation V_i=Ar³–Bz²/r by means of linear regression analyses, assuming (i) only that all cations or anions obey the equation, (ii) the value of A is the same for cations and anions and the value of B is the same for cations and anions. Pauling, Goldschmidt, and Gourary and Adrian ionic radii were used in the analyses. The values of V(Cl^–) obtained using the two former radii are in good agreement with the best literature values. An analysis of the effect of temperature on A and B shows that A increases to a maximum at about 100° and B reaches a minimum at about 50°; the combined result is that V_i reaches a maximum, the position of which depends mainly on the charge of the ion but also on the radius. It is proposed that an extra structural term should be included in the equation to account for the partial molal volumes of ions at temperatures below 100°C.