Determination of Dissociation Constant of Hydrogen Cupferrate in Methanol-Water and 2-Propanol-Water Solution

[摘要] The glass electrode was empirically calibrated in methanol-and 2-propanol-water mixed solvents, by means of which the pH-meter reading could be converted to stoichiometric hydrogen ion concentration. The thermodynamic dissociation constants of hydrogen cupferrate in methanol-and 2-propanol-water solution were potentiometrically determined with the changes in composition of organic solvents at 0.01 and 0.05 of the ionic strength and 25¡É. The empirical formula of the constants with mole fraction (n) of the organic solvent are as follow: methanol-water solution pKa= 2.24n + 4.29 at ¥ì = 0.01 n = 0.0476¡­0.642pKa = 2.35n + 4.38 at ¥ì = 0.05 n= 0.0446~0.642 2-propanol-water solution pKa= 5.50n + 4.48 at ¥ì = 0.05 n = 0.0253~0.259 The relationships between pKa of acetic acid, propionic acid and HCup and dielectric constant of some mixed solvents were discussed. It would be considered that the factors effecting pKa value of weak acid in mixed-solvent are not only dielectric constants but acid-base character and solvation effect of the solvent, etc.

[学科分类] 化学（综合）