Applications of the solubility product relation

In spite of its limitations (as outlined in the previous section) the solubility product relation is of great value in qualitative analysis, since with its aid it is possible not only to explain but also to predict precipitation reactions. The solubility product is in reality an ultimate value which is attained by the ionic product when equilibrium has been established between the solid phase of the slightly soluble salt and the solution. If conditions are such that the ionic product is different from the solubility product, the system will seek to adjust itself in such a manner that the ionic product attains the value of the solubility product. Thus, if the ionic product is arbitrarily made greater than the solubility product, for example by the addition of another salt with a common ion, the adjustment of the system results in the precipitation of the solid salt. Conversely, if the ionic product is made smaller than the solubility product, as, for instance, by diminishing the concentration of one of the ions, equilibrium in the system is attained by some of the solid salt passing into solution. 

As an example of the formation of a precipitate, let us consider the case of silver chloride. The solubility product is 

Let us suppose that to a solution which is 0-1 molar in silver ions we add enough potassium chloride to produce momentarily a chloride concentration 0 01 molar. The ionic product in such a case would be 01 xO Ol = 10 3. As 10 3 1-5 x 10 10, equilibrium will not exist and precipitation of silver chloride will take place 

Attention must also be drawn to the fact that complete precipitation of a 

On the basis of this general discussion, we can now consider some direct applications of the solubility product principle to quantitative inorganic analysis. 

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