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本文用电位pH法测定了在20.0±0.1℃温度下以NaNO_3为支持电解质,在乙醇—水混合溶剂中Tiron的酸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,溶液的离子强度变化范围为I=0.1-4.0mol dm~(-3)。混合溶剂中乙醇的重量百分数分别为0,5,15,25,35和50wt％。用基于Pitzer方程式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。该常数的对数值logK_0与混合溶剂中有机组分摩尔分数X以及混合溶剂介电常数D遵从下列经验关系: logK_0=k_x X+C_1 logK_0=k_D 1/D+C_2式中k_x,k_D,C_1和C_2皆为经验常数。
In this paper, the acid dissociation constant of Tiron with NaNO_3 as the supporting electrolyte at 20.0 ± 0.1 ℃ was measured by potentiometric pH method and the change law of the constant with ionic strength and solvent composition of the solution was investigated. The ionic strength of the solution varies in the range of I = 0.1-4.0 mol dm ~ (-3). The weight percentage of ethanol in the mixed solvent was 0, 5, 15, 25, 35 and 50 wt%, respectively. The thermodynamic dissociation constants of acids in mixed solvents with different compositions were determined by the least square polynomial approximation based on the Pitzer equation. The logarithm value of this constant logK_0 and the molar fraction of organic components X in the mixed solvent and the dielectric constant D of the mixed solvent follow the empirical relationship: logK_0 = k_x X + C_1 logK_0 = k_D 1 / D + C_2 where k_x, k_D, C_1 and C_2 are all empirical constants.