Question

A key clever aspect of the Job plot method is keeping the total number of moles of both reagents constant- increasing one while decreasing the other. Another approach to determining stoichiometry more closely resembles a titration. In this method, you keep constant the moles of metal (or cation) and add increasing amounts of ligand (or anion) while monitoring abso rbance of the product (MLn) being formed. The concentration of the ligand solution you are adding is often quite concentrated so the total volume of your sample remains relatively constant. Draw a plot of [MLn] (concentration of product) vs. moles addedduring such a titration.

Provide a short explanation of how you would determine the stoichiometry.

Answer 1

Initially, with increase in no.of moles of ligand, the concentration of product [ML_n] increases. After some time when all the metal ions are consumed in making complex further addition of ligand will not affect the absorbance and concentration of product becomes constant. This is called equivalence point. Using the value of no. of moles of ligand at equivalence point and metal ion concentration stoichiometry can be determined.