THE INVESTIGATION OF COMPLEX-FORMATION EQUILIBRIA AT CONSTANT IONIC-STRENGTH

The inert salts used for the investigations of complex formation are briefly discussed in relation to the effects of their ions on the equilibria studied. In general, some association with the inert salt ions cannot be completely avoided. In case of very stable complexes measured at low ionic strength, their effects can be quantified even though they are not caused by the anion if NO3- or ClO4- are used. In the case of weak complexes, when ionic strengths I greater-than-or-equal-to 1 are used, the concentration of the complex of interest ran be 1000 times lower than that of the associates of the same cation with the anion of the inert salt causing difficulties with the investigation of the latter systems. If the experimental results for K1 of the alkaline-earth metal ions with fluoride in sodium perchlorate and sodium nitrate are correct, as their equilibrium constants have very similar values, it follows that the behavior of two anions is very similar. However, if NO3- associates with the above cations, as found, the same behavior is expected for ClO4-. A more accurate analysis can only be done if activity coefficients in these solutions are known.