Determination of Dissociation Constant of Hydrogen Cupferrate in Water, Dioxane-Water, and Ethanol-Water Solution

[摘要] The glass electrode was empirically calibrated in dioxane-and ethanol-water mixed solvents, by means of which the pH-meter reading could be converted to stoichiometric hydrogen ion concentration. By the potentiometric titration method, the thermodynamic dissociation constants of hydrogen cupferrate (HCup) with variations of ionic concentration in aqueous solution were determined, and by the extrapolation of the constants the new thermodynamic pKavalue, 3.980¡¾0.006, at zero ional concentration was obtained. The thermodynamic dissociation constants of HCup in dioxane-and ethanol-water solution were also potentiometrically determined with the changes in composition of organic solvents at 0.01 and 0.05 of the ionic strength(¥ì) and 25 ¡É. The empirical formula of the constants with mole fraction(n) of the organic solvent are as follow: Dioxane-water solution. pKa= 12.96n + 4.10 at ¥ì = 0.01, n = 0.0228¡­0.171 pKa= 12.05n + 4.23 at ¥ì = 0.05, n= 0.0228¡­0.171 Ethanol-water solution, pKa= 4.0ln + 4.26 at ¥ì= 0.01, n= 0.0395¡­0.262 pKa= 3.83n + 4.34 at ¥ì = 0.05, n= 0.0395¡­0.262

[学科分类] 化学（综合）