Conductivity and Association Constants of Symmetrical Weak Electrolytes

Molar Conductivity and Association Constants of Symmetrical Weak Electrolytes 

When ion association occurs in the solution of a (z, z)-type electrolyte, Eq. (7.3) holds  

This effect is called the relaxation effect. Second, in the presence of the ionic atmosphere, a viscous drag is enhanced than in its absence because the atmosphere moves in an opposite direction to the moving ion. This retarding effect is called the electrophoretic effect. In Eq. (7.1), the Ah°°-term corresponds to the relaxation effect, while the E-term corresponds to the electrophoretic effect. For details, see textbooks of physical chemistry or electrochemistry. 

c is the total concentration of MA, KA is the association constant, a is the degree of dissociation of the ion-pair M2+A2h and y is the average activity coefficient of free ions of concentration ca. Because the ion-pairs do not conduct electricity, the molar conductivity A in the presence of ion association is less than in its absence. In Fig. 7.1, the difference between the experimental molar conductivity (A) and the value calculated from Eq. (7.1), /lcai, are plotted against c1/2 for lithium halides in sulfolane [la]. For Lil, the difference between A and /lcai is small because ion association is not appreciable (KA=5.( mol-11). For LiBr (KA = 278 mol-11) and LiCl (KA= 13860 mol-11), however, A is much smaller than 

When ion association occurs, the relation A = aA holds between the molar conductivity for free ions (concentration ca), Ay, and that for total electrolyte concentration, A. Thus we get Eq. (7.4) from Eq. (7.3)  

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