Comparison of activity of hydroxide and alkoxide ions based on acidity functions

Abstract

Comparison of acidity functions H_–, H_M, J_–, J_M corrected for the change in ionic product or protolytic constant indicates that up to a concentration of ca. 3.0 mol dm^–3 in sodium hydroxide or alkoxide these functions are virtually identical. Specific solvent–solute interactions result in the differences at higher base concentrations. To estimate values of H_x in mixtures of water with alcohol X values of H_– in aqueous solutions are combined with values of log_my_i(transfer activity coefficients or medium effects). Acidity functions J_– are a linear function of a_OH^–. The deviation of the slope of this line (1.233) from unity can be either due to the fact that y_OH^– is larger than y_±NaOH and that this difference varies with the concentration of the hydroxide or that the value of the ratio y_SH/y_SHOH^– for the indicator used only approximates unity. Deviation of the values of this ratio from unity can be explained on the basis of the Debye–Hückel theory. Water and lower straight-chain alcohols show acid–base properties which are strongly analogous both qualitatively and quantitatively.