Constant solubility-product

The solubility product constant is a usefnl parameter for calculating the aqueous solubility of sparingly solnble compounds under various conditions. It may be determined by direct measnrement or calculated from the standard Gibbs energies of formation AfG° of the species involved at their standard states. Thus if = [M+] x [A ] is the equilibrium constant for the reaction 

The solubility product constant is calculated from the equation 

We can develop a totally general expression by using an exact analogy to the approach taken for metal complexes (Chapter 5) to deal with side reactions involving either or both the cation and/or the anion. In the solubility product equilibrium expression for M X, simply substitute the equivalent aC expressions for the concentrations of each ioa Then 

When the precipitating anion is a Bronsted base, then its concentration is pH dependent and, therefore, so is the solubility of the precipitate. Let us consider a few examples. 

So far we have discussed mainly compounds that are quite soluble in water. Although most compounds dissolve in water to some extent, many are so shghdy soluble that they are called insoluble compounds. We shall now consider those that are only very shghdy soluble. As a rule of thumb, compounds that dissolve in water to the extent of 0.020 mole/ liter or more are classified as soluble. Refer to the solubihty guidelines (see Table 6-4) as necessary. 

The calcium carbonate, CaCOs, in an eggshell has the same crystal structure as In the mineral calcite. 

In equilibria that involve slightly soluble compounds in water, the equilibrium constant is called the solubility product constant, The activity of the pure solid BaS04 is one 

The concentration of the soUd is never included in the equilibrium constant expression. 

For a saturated solution of BaS04 in contact with solid BaS04, we write 

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ELECTROLYTES, EME, AND CHEMICAL EQUILIBRIUM TABLE 8.6 Solubility Product Constants Continued)... 

Solubility Product — The solubility product constant commonly referred to as the solubility product provides a convenient method of predicting the solubility of a material in water at equilibrium. Copper hydroxide, for example, dissolves according to the following equilibrium ... 

Note that the brackets, [ ], refer to the concentration of the species. K,p is the solubility product constant hence [Cu " ] and [OH] are equal to the molar concentrations of copper and hydroxyl ions, respectively. The K p is commonly used in determining suitable precipitation reactions for removal of ionic species from solution. In the same example, the pH for removal of copper to any specified concentration can be determined by substituting the molar concentration into the following equation ... 

Click Coached Problems for a self-study module on solubility product constant expressions. 

Precipitate Formation Solubility Product Constant (ffsp)... 

One way to establish equilibrium between a slightly soluble solid and its ions in solution is to stir the solid with water to form a saturated solution. As you might expect, the solubility of the solid, s, in moles per liter, is related to the solubility product constant, Ksp. In the case of barium sulfate dissolving in water we have... 

Using AG tables in Appendix 1, calculate the solubility product constant, Rsp, for PbCl2 at 25°C. 

The general approach illustrated by Example 18.7 is widely used to determine equilibrium constants for solution reactions. The pH meter in particular can be used to determine acid or base equilibrium constants by measuring the pH of solutions containing known concentrations of weak acids or bases. Specific ion electrodes are readily adapted to the determination of solubility product constants. For example, a chloride ion electrode can be used to find [Cl-] in equilibrium with AgCl(s) and a known [Ag+]. From that information, Ksp of AgCl can be calculated. 

K. See Equilibrium constant Ka. See Acid equilibrium constant See Base equilibrium constant Kc. See Equilibrium constant Kf. See Formation equilibrium constant Kr See Equilibrium constant K,p. See Solubility product constant K . See Water ion product constant K-electron capture The natural radioactive process in which an inner electron (n = 1) enters the nucleus, converting a proton to a neutron, 514 Kelvin, Lord, 8... 

It is important to note that the solubility product relation applies with sufficient accuracy for purposes of quantitative analysis only to saturated solutions of slightly soluble electrolytes and with small additions of other salts. In the presence of moderate concentrations of salts, the ionic concentration, and therefore the ionic strength of the solution, will increase. This will, in general, lower the activity coefficients of both ions, and consequently the ionic concentrations (and therefore the solubility) must increase in order to maintain the solubility product constant. This effect, which is most marked when the added electrolyte does not possess an ion in common with the sparingly soluble salt, is termed the salt effect. 

K,p is also called the solubility product constant and, most simply, the solubility constant. 

Use the table below to answer question 4. Solubility Product Constants at 298K... 

If S moles of CaCC>3 dissolve in a liter of water, then S moles each of calcium ion and carbonate ion form. With these ion concentrations equal to S, the solubility of CaCC>3 is calculated as 9.3 x 10 5 M. The higher solubility of magnesium carbonate in water, 6.3 x 10 3 M, results from the larger solubility product constant. Nevertheless, both of these carbonate salts are rather insoluble, and the excess carbonate anions provided by the sodium carbonate effectively precipitate the calcium and magnesium ions from solution. 

Table 3.9. Solubility product constants of common compounds and minerals of selected major and trace elements at 25 °Ca...

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