The effect of complexing on solubility equilibria

Ion pair formation, or complex formation, is indicated when the solubility of a sparingly soluble salt increases in the presence of an ion which could form an ion pair, or with a ligand which could form a complex with one of the ions of the salt. In these cases there are at least two equilibria, and all must be satisfied simultaneously. 

Calcite was added to a solution of edta laq) until no more solid would dissolve. The concentration of the complex was found to be 0.042 mol dm . Find the concentrations of edta (aq) remaining and of the free Ca (aq) in solution. 

Addition of the chemical equations for the first two equilibria gives the third. This is the reaction for which the equilibrium constant is required. Addition of the chemical equations corresponds to multiplication of the equilibrium constant relations  

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