Comparison of temperature, pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

Abstract

The limiting molar conductances Λ° of potassium deuteroxide KOD in D2O and potassium hydroxide KOH in H2O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD− (OH−) and a D3O+ (H3O+) ion. The excess conductances of the OD− ion in D2O and the OH− ion in H2O, λ E 0 (OD-) and λ E 0 (OH-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, λ E 0 (D+) and λ E 0 (H+). However, the temperature effect on the excess conductance is larger for the OD−(OH−) ion than for the D3O+ (H3O+) ion but the pressure effect is much smaller for the OD− (OH−) ion than for the D3O+ (H3O+) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD− (OH−) ion than for the D3O+ (H3O+) ion. Concerning the isotope effect, the value of λ E 0 (OH-)/λ E 0 (OD-) deviates considerably from\(\surd 2\) at each temperature and pressure in contrast with that of λ E 0 (H+)/λ E 0 (D+), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD− (OH−) or the D3O+ (H3O+) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D2O and H2O, and their variations with temperature, pressure, and isotope.