Solvation of ions. XXV. Partial molal volumes of single ions in protic and dipolar aprotic solvents

Partial molal volumes at 25° are reported for some 1 : 1 electrolytes, and for triphenylmethane, in dimethyl sulphoxide, N,N- dimethylformamide, acetonitrile, propylene carbonate, formamide and hexamethylphosphoramide. The assumption that ?V°tr(Ph4As+) = ?V°tr(BPh4-) was used to obtain ionic partial molal volumes of transfer from water to the non-aqueous solvents. Solvent compressibility appears to determine the partial molal volumes of non-electrolytes and large hydrophobic ions in solution. Values of ?V°tr for cations and anions are discussed in terms of ion-solvent interactions, solvent-solvent interactions and steric crowding of large solvent molecules around the ions.