RESUMO
Potentiometric measurements have been applied to the determination of ionization constants for water in binary ethanol-water mixtures. The effects of solvent composition and temperature were studied. The pK value showed an increase with increasing of ethanol content and decreasing with increasing temperature. The variation of pK with the ethanol content was attributed to the effect of the variation of the dielectric constant of the medium. The values of delta G and delta S for 20.8 wt% ethanol-water mixture were calculated [82.5 k J. mole[-1]and 90.2 J. deg[-1]mole[-1]respectively] and compared to that in pure water [81.2 k J. mole[-1]and 81.0 J. deg[-1mole[-1respectively]. The difference was due to the decrease in the dielectric constant and the increase in the basicity by the presence of ethanol