Hydrolysis of Cations in Water and Ionic Potential

Two interesting conclusions derive from Eqs. (3.42) to (3,46). First, the fraction of Cd present as each species is independent of the total Cd concentration. (This is true when only mononuclear Cd complexes are present, but would not be true in the presence of polynuclear Cd complexes, that is, Cd complexes that contained more than one atom of Cd). The second noteworthy conclusion is that higher chloride complexes increase rapidly in relative importance with increasing total chloride. This is because the concentration of each complex is proportional to (Cl ) , where n is the number of Cl groups in the complex. 

In preceding expressions (Cl ) denotes the concentration of free or uncomplexed chloride. Total chloride is given by the mass-balance equation 

The answer to Example 3.2 can be read directly from Fig. 3.3 or found by substitution into Eqs. (3.42) to (3.46). First, given that (Cl ) - 1.00 M (pCI = 0), we solve for the fractional values. These are then multiplied times XCd = 0.010 M, the total analytical Cd concentration to obtain amounts of the individual species. 

They equal the same values determined in Example 3.2. Usually fractional species curves such as are shown in Fig. 3.3 are plotted together in one figure to save space and for more direct comparison of the relative importances of the species. 

The dipolar nature of the water molecule (see Fig. 3.1) is an important property of water that influences its interactions with cations. Because of its dipolar character, charge is unevenly distributed at the surface of each water molecule, and the protons of one molecule attract the oxygens of adjacent water molecules. This attractive force is called hydrogen bonding and relates to e, the dielectric constant of water. The dielectric constant is a measure of a. solvent s ability to dissolve ionic solids and 

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