Pressure Effect on Proton Jumps in t-Butyl Alcohol–Water Mixtures at 25°C

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Abstract
The limiting molar conductances, Λ°, of hydrochloric acid and potassium chloride in 2,3,5,7,10, and 25 mol% t-butyl alcohol (TBA)–water mixtures were determined at 25°C as a function of the pressure up to 2000 kgf cm−2 (1 kgf cm−2=0.9807×105 Pa) from the conductances measured within a dilute concentration range. In each solvent mixture the value of Λ° (HCl) was about three- to five-times larger than that of Λ° (KCl) The anomalous excess proton conductance, λ°E, as estimated by the equation [λ°E=Λ° (HCl)−Λ°(KCl)], was found to increase with increasing pressure in 2,3,5,and 7 mol% TBA–water mixtures, but to decrease in 10 and 25 mol% TBA-water mixtures. The rate of increase with pressure of the excess proton conductance normalized to the molar concentration of water in the mixture was largest in a 2 mol% TBA mixture, and its magnitude decreased in the order: 2>3>0>5>>7>>10>>25 mol% of TBA. These results are compared with those obtained in ethanol–water mixtures and are discussed in relation to the effect of alcohol molecules on the water structure in the mixtures: the three-dimensional network of water in TBA–water mixtures is more stable at a lower mol% of alcohol, and collapses more rapidly with increasing alcohol content than in ethanol–water mixtures.

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