The thermodynamic functions of complex formation of benzo-15-crown-5 ether (B15C5) and sodium cation (Na+) in acetone–water mixtures at 298.15 K have been calculated. The equilibrium constants of B15C5/Na+ complex formation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured
by the calorimetric method. The complexes are enthalpy-stabilized but entropy-destabilized in acetone–water mixtures. The
effects of hydrophobic hydration, preferential solvation of B15C5 by a molecule of water and acetone, respectively and the
solvation of Na+ on the complex formation processes have been discussed. The calculated thermodynamic functions of B15C5/Na+ complex formation and the effect of benzene ring on the complex formation have been compared with analogous data obtained
in dimethylsulfoxide–water mixtures. The effect of carbonyl atom replacement in acetone molecule by sulphur atom (DMSO molecule)
on the thermodynamic functions of complex formation has been analysed.