Physico-chemical studies on acidity functions in mixed solvents VI Studies on the acidity function H of solutions of KOH in ethanol water mixtures

ABSTRACT

The values of H[-] are computed for solutions of different concentrations of KOH in ethanol-water mixtures, from the spectrophotometric measurements of ultraviolet absorption of p-nitroaniline, o-nitroaniline, phenol and thioacetamide which arc structurally different indicators. The mean values H[-] and their standard deviations are given together with these deviations expressed in percent. The values of S mean fall between +/- 0.12 percent and +/- 2.05 percent, depending on alkali hydroxide concentration and solvent composition. These reasonable values of S mean denote that H[-] is more or less independent of the indicator used, which may be taken as an evidence in support of the validity of HEI as a measure of acidity in the investigated solutions. Such a validity is also emphasized by the linear plots of unit slope, relating the logarithm of the indicator ratio I and H[-] for the four indicators in solutions of different concentrations of KOH in ethanol water mixtures. The parameters of the linear relationship between H[-] and the reciprocal of the KOH concentrations are also computed by the use of the least-squares method. These parameters facilitate the calculation of the value of H[-] for any other concentration of KOH in the same mixtures. The plots of H[-] against alcohol content in mole percent disclose several peaks and minima the location of which depend on the base concentration and indicator used for the determination of H[-]. This is explained in terms of solvent-solvent and solute-solvent interactions. The values which are computed for K['],K degree, [OH[-]], [r-p-I], and log f[f/m] reflect the effects of these interactions in defining the basicity of the different solutions examined