Conductance of the hydroxide ion in tert-butyl alcohol-water and 1,4-dioxane-water mixtures

Limiting molar conductances Lambda(o), of potassium hydroxide in 2 to 25 mol% tert-butyl alcohol (TBA)-water mixtures were determined at 25 degrees C as a function of pressure up to 196 MPa. Lambda(o)'s of KOH in (2.5 to 15 mol%) 1,4-dioxane-water mixtures at 25 degrees C and 1 atm were also determined. The excess conductance lambda(o)(E) of the OH- ion estimated as [lambda(o)(E)(OH-) = Lambda(o)(KOH) - Lambda(o)(KCl)] decreased with an increase in the TEA or dioxane content, as did the excess proton conductance lambda(o)(E)(H+)[lambda(o)(E)(H+) = Lambda(o)(HCl) - Lambda(o)(KCl)]. Although lambda(o)(E)(OH-) is smaller than lambda(o)(E)(H+) at all solvent compositions studied, the rate of decrease in lambda(o)(E) with organic content is larger for the OH- ion than for the H3O+ ion in both solvent mixtures except in the water-rich region of TBA-water mixtures. lambda(o)(E)(OH-) increases with pressure more strongly in TEA-water mixtures than in pure water, and the rate of increase in lambda(o)(E)(OH-) with pressure has a maximum at 5 mol% of TEA. These results are discussed in terms of the difference in stability of hydrogen bonds between the OH- or the H3O+ ion and water molecules and the increase in repulsive forces due to the orientation [H-O O-H] of water molecules in the mixtures.