CALCULATIONS OF SPECIATION OF ASSOCIATED SOLUTIONS FROM VAPOR-PRESSURE COMPOSITION DATA

A new method is described for calculating the equilibrium speciation of a binary mixture (A + B) in which the two components interact to form a 1:1 complex (AB). As experimental input, the method requires total solution vapour pressures (P(T)) at known stoichiometric compositions (x(i)). This is in contrast to the method that is currently in common use (here called the old method) which requires equilibrium vapour phase compositions (y(i)). By eliminating the need for values of y(i) which are notoriously difficult to determine precisely, the new method is able to produce results that have smaller uncertainties than those obtained from the old method. The new method is also simpler to use than the old method. The advantages of the new method are illustrated by applying both methods to a set of experimental data. The importance of having the best possible values for the equilibrium speciation is discussed.