Measurement of solvent isotope effects with the glass electrode. Part I. The ionic product of D2O and D2O–H2O mixtures

Abstract

The ionic product of D₂O and D₂O–H₂O mixtures has been determined by means of a cell with glass and silver–silver chloride electrodes and without liquid junctions. The experimental data were obtained from a study of the stepwise addition of barium hydroxide solution to hydrochloric acid which was initially in the cell. A computer program was used to evaluate the data and to assist in the minimisation of uncertainties associated with the glass electrode and the electrolyte composition. The isotope effect, ΔpK_n= pK_n– pK_H is given by the equation ΔpK_n= 0·7282n+ 0·0512n²+ 0·0826n³. Interpretations based on a monosolvated proton are superior to those in which the solvation is unspecified. There is some evidence for fractionation processes associated with water molecules in the solvent shells of H₃O⁺ and OH^– ions or for some other form of medium effect.