Jobs Method of Continuous Variations

Another method for determining the composition of a complex in solution is that known as Job s method or the method of continuous variations. Suppose that the formation of a complex between metal A and m ligands B can be shown as 

A series of solutions can now be prepared such that the total concentration of metal and ligand is a constant, C, 

It is easy to verify that the curve representing the measured property will exhibit a maximum or minimum at the same ratio of concentrations as the constituents that are present in the complex. We can write the expression for the equilibrium constant as 

Since we want to find out if the change in concentration of the complex with the change in concentration of B goes through a maximum or minimum, we need to take the derivative and set it equal to 0  

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