Chapter 7 Solutions of Electrolytes. 7.1 transference of ion 7.2 conductance of electrolyte solution 7.3 Application of conductance 7.4 Strong Electrolytes. New Words and Expressions. galvanic cell 原电池 electrolytic cell 电解池 Cathode 阴极
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Consider an electrolyte of formula AaBb, which ionizes as follows:
AaBb == aAz+ + bBz-
a-b type of electrolyte
7.1 transference of ion
The speed with which the ion moves under a unit potential gradient.
The SI unit of it is m2·V-1· S-1.
Together with: az+=bz-
1. Hittorf Method
2. Moving Boundary Method
cell constantK cell =l/A (7.6) SI unit:m-1,
m = m - Ac1/2 (7.8)
(dilute solution of strong electrolytes)
AB === A+ + B-
EXAMPLE 7.1 The value of HAc solution at 25oC is 5.20110-4 S·m2·mol-1, what is the degree of dissociation and the equilibrium constant Kc of HAc.
Because of the limit concentration, so
(Salt) = (Solution) - (Water)
EXAMPLE 7.2 The values of AgCl solution and solvent H2O at 25oC is 3.1410-4 and 1.6010-4 S·m-1respectively. what is the solubility and solubility products of AgCl.
Ironic mean activity and ironic activity factor
离子平均活度（mean activity of ions）
离子平均活度系数（mean activity coefficient of ions
离子平均质量摩尔浓度（mean molality of ions）
Where ci is the molar concentration of the ions of type i, zi is the valence of the ions.
EXAMPLE 7.3 Calculate the ionic strength of: (1) The solution of 1.0mol·kg-1KCl and 1.0mol·kg-1K2SO4respectively at 25oC; (2) The solution containing both of 0.001mol·kg-1CaCl2 and 0.002 mol·kg-1Na2SO4 at 25oC.
1. The decrease in the molar conductivity of a strong electrolyte was attributed to the mutual interference of the ions, which becomes more pronounced as the concentration increases.
2. Because of the strong attractive forces between ions of opposite sighs, the arrangement of ions in solution is not completely random.
This is known as the Debye-Huckel limiting law
EXAMPLE 7.4 Applying the Debye-Huckel limiting law, (1) Calculate the activity coefficient of Zinc ion in the solution containing both of 0.002mol·kg-1CaCl2 and 0.002 mol·kg-1 ZnSO4 at 25oC (2) Calculate the mean activity coefficient of The solution of 0.001mol·kg-1 K3Fe(CN)6 at 25oC;.