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用电位滴定法测定了在２９３±０．Ｋ时以ＮａＣｌＯ＿４为支持电解质、在乙醇－水混合溶剂中变色酸（ＣＴＳ：３，６－二磺酸钠－１，８－二羟基萘酚）的解离常数，并考察了该常数随溶液离子强度和溶剂组成的变化规律。溶液离子强度的变化范围为Ｉ＝０．１～４．０ｍｏＬｄｍ－３，溶剂中乙醇的重量百分数为０－５０％。用基于Ｐｉｔｚｅｒ方程的最小二乘多项式逼近法确定了各种不同组成的混合溶剂中酸的热力学解离常数发现该常数的对数值ｌｇＫ＿０与混合溶剂中有机组分的摩尔分数（ｘ）及混合溶剂的介电常数（Ｄ）遵守下列经验公式：式中Ｋ＿ｘ、Ｋ＿Ｄ、Ｃ＿１和Ｃ＿２皆为经验常数。
Potentiometric titration was performed at 293 ± 0. K as NaClO_4 as a supporting electrolyte, in a mixed solvent of ethanol and water, the dissociation constant of chromotropic acid (CTS: sodium 3,6-disulfonate-1,8-dihydroxynaphthol), and investigated the constants with the solution Ionic strength and solvent composition changes. The ionic strength of the solution varied in the range of I = 0.1 ~ 4.0moLdm-3, and the weight percentage of ethanol in the solvent was 0-50%. The thermodynamic dissociation constants of acids in mixed solvents with different compositions were determined by the least square polynomial approximation method based on the Pitzer equation. It was found that the logarithm of this constant, lgK_0, and the mole fraction of organic components in the mixed solvent (x) and the mixed solvent The dielectric constant (D) obeys the following empirical formula: where K_x, K_D, C_1 and C_2 are empirical constants.