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Abstract

The quantity metachor introduced in the preceding paper was evaluated from the experimental data on surface tension of the aqueous solutions for a set of polyvalent and weak electrolytes. The almost complete concentration independence of the metachor and its direct proportionality to the number of the free charges in a dissociated molecule (observed and theoretically substantiated in the above cited paper for strong 1,1-, 1,2- and 2,1-valent electrolytes) has been verified in the present paper also for electrolytes of the higher valency types. The metachor values of fully dissociated 1,1-, 1,2-, 1,3- and 1,4-valent electrolytes follow a ratio (5 ± 1) : (10 ± 1.5) : 15 : 22 cm³ mol^-1. Association of the electrolytes decreases correspondingly the metachor value as one can see on the case of electrolytes with bulky ions (NH₄SCN, KCH₃COO, Na₂S₂O₃, hexacyanoferrates(II) or with the free acids H₂SO₄, H₂CrO₄, H₃PO₄ etc. A weak, in the investigated concentration range neglibility dissociated oxalic acid, consisting of small hydrated hydrophilic molecules, exhibits metachor values close to zero. Dibasic organic acids with a larger number of hydrophobic CH₂ groups reach very high negative metachor values, however, their salts again possess metachor values close to 10 cm³ mol^-1 - in accordance with the values found for strong 1,2-valent electrolytes. The metachors of ZnCl₂ and CdCl₂ decrease sharply from the last mentioned value, with increasing concentration while the metachor value of zinc perchlorate remains unchanged at the level corresponding to the fully dissociated salt. This is in agreement with the well known sequence of tendency of the d¹⁰-cations to form complexes with the Cl^- and ClO^-₄ anions. All these facts have verified that the metachor can be, in principle, applied for a diagnostic states of the electrolytes in aqueous solutions.