Effect of Foreign Complexing Agents

If a slightly soluble salt MA is treated with a complexing agent L, the following equilibria are involved  

The fraction a i of the metal ion in the uncomplexed form M may be calculated. The total metal ion concentration Cm is given by 

The effect of complex formation is to increase the solubility in proportion to the square root of the decreasing fraction of metal ion in the uncomplexed form. Similar considerations may be applied to more involved types of precipitates. 

EXAMPLE 7-6 Calculate the solubility of silver iodide in 0.01 M ammonia, if the solubility product of silver iodide is 9 x 10 and the logarithms of the successive formation constants of the silver-ammonia complexes are 3.2 and 3.8. 

Note that the concentration of AgCNKj) is small compared with that of Ag(NH3)2 . 

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