Dissociation constant of benzoic acid in H2O + D2O mixtures

Abstract

The dissociation constant of benzoic acid has been determined at 25°C in ordinary water and in H₂O + D₂O mixtures by conductance measurements and by precise e.m.f. measurements with glass and silver–silver chloride electrodes in a cell without liquid junctions. The isotope effects Δ_pK_n(=_pK_n–_pK_H) obtained by the two methods are in agreement and are shown to support the simple equilibrium theory of solvent isotope effects. The values of _pK_H and _pK_D obtained from the e.m.f. measurements are 4.201±0.004 and 4.693±0.004 respectively.