On the Use of the Molar Ratio Method for Determining Association Stoichiometry

In the molar ratio method, a property of a solution is plotted against the molar ratio of the two reactants, the concentration of one being kept constant. The stoichiometry of the complex or complexes formed is deduced from the position of breaks in the curve. The method is examined critically, and is shown to be inapplicable to most problems, owing to the nonrealization of the required assumptions of linear dependence of the property on the partial molar properties of the interacting species and constancy of activity coefficients, in addition to the mathematical difficulties involved in relating the breaks in the curves to the stoichiometric ratio in the complex.