活度系数法测定A2B型难溶盐的溶度积——以Ag2SO4为例

实验假设水溶液中Ag+和SO42－的浓度非常低时，其活度无论处于同一体系还是在不同体系均相同。依此设计原电池，使该原电池的电池反应为Ag2SO4(s)→2Ag+(aq)+SO42－(aq)，采用补偿法测量一定温度下此原电池中AgNO3溶液浓度和K2SO4溶液浓度发生变化时的电池电动势E。依据能斯特方程和Debye-Huckel极限公式，推导出原电池标准电动势E?与电解质的平均活度系数γ±及溶液浓度的关系，用外推法作图得到此电池反应的标准电动势E?。由平衡常数与原电池标准电动势的关系，得到Ag2SO4的溶度积Ksp(Ag2SO4)。

Solubility Product Determination of A2B Type Insoluble Salts by the Activity Coefficient Method:Taking Ag2SO4 as an Example

Taking the assumption that activity of silver ion and sulfate ion of very low concentration is constant in any aqueous solution,the primary cell was designed for the cell reaction of Ag₂SO₄(s)→2Ag⁺(aq)+SO₄^2-(aq).The compensation method was used to obtain the electromotive force of the primary cell when the concentrations of AgNO₃ and K₂SO₄ changed.The relationship between electromotive force and the mean activity coefficients of electrolytes as well as the solution concentration was deduced according to the Nernst equation and the limit Debye-Huckel formula.Standard electromotive force E ^⊖ was obtained by extrapolation.Finally,the solubility product of silver sulfate was calculated through the relationship between equilibrium constant and electromotive force of the primary cell.