Complex Equilibria Involving Several Complexing Agents

METAL COMPLEX EQUILIBRIA INVOLVING SEVERAL COMPLEXING AGENTS 

In general, the values ofaj in mixtures of ligands can be obtained from the combination of values for the individual ligands. After all, is 

Examining Equation 5-8, we notice that the nominator has only one [M] term rather than N such terms needed when N ligands are present. This may be rectified by adding (N-1) [M] terms and subtracting an equal number. Then Equation 5-8 becomes 

The second term in Equation 5-9 may be neglected in most problems, since when complexation is significant 1/aj (N-1). In practice, one ligand is usually stronger than the rest so that calculated for this ligand alone remains essentially the same after the other ligands are considered. This can easily be inferred from Equation 5-9. 

Calculate the for a solution in which the equilibrium concentration of EDTA, [Y ] = 10. Recalculate a when ammonia is also present at 

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