<原報>Titroprocessor を用いた含水溶媒中における有機酸の酸塩基滴定

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100μmol of acetic, benzoic or salicylic acid in the mixture of water and methanol, ethanol or acetone is titrated potentiometrically by 0.1M NaOH using Metrohm titroprocessor with the glass indicator and silver-silver chloride reference electrodes, and a salt bridge of 3M LiCl aqueous ethanol solution. (Figs. 1 and 2,Table I) For the determination of monobasic organic acids, soluble in water, the titration in water is preferable to that in aqueous organic solvents, because the dielectric constant of the solvents is lower than that of water, and the strength of the acid is weaker in the mixture of solvents than in water. 100μmol of some dibasic acids of neutral molecule can be differentially titrated in aqueous organic solvents if the difference of pK_1 and pK_2 of the acid is larger than 1.4 using the titroprocessor. (Figs. 3-5,Table II) According to increase of the portion of organic solvent, the difference of emf between half-neutralization point and three-second point (⊿E[3/2-1/2]) increases, but the difference between three-second and five-second point (⊿E[5/2-3/2]) decreases. [chemical formula] The effect of the dielectric constant and the acidity of solvents on emf of the half-neutralization point is discussed. (Figs. 7 and 8)
1980-03-25