The metachors of polyvalent and associated electrolytes in aqueous solutions

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.

Modeling Surface Tension of Concentrated and Mixed-Solvent Electrolyte Systems

“…Surface tension of aqueous phosphoric acid solutions as a function of x H 3 PO 4 at various temperatures. The experimental data were taken from Abramzon and Gaukhberg − and Celeda et al …”

“…Surface tension of the H 2 SO 4 + water system as a function of x H 2 SO 4 at various temperatures. The experimental data were taken from Livingston et al, Sabinina and Terpugov, Celeda et al, Pozin and Tumakina, and Myhre et al …”

“…In particular, a significant amount of neutral acid molecules appears as the acid concentration approaches a mole fraction of 1 and association becomes nearly complete in a pure acid. 41 The interaction parameters that are used in the model for this type of systems include the Γ ik σ,0 and K ik parameters between ionic species in eq 17a and the τ ji , τ ij , and k ji parameters between 38 Sabinina and Terpugov, 39 Celeda et al, 55 Pozin and Tumakina, 56 and Myhre et al 40 Here, it should be noted that neutral acid molecules take on the meaning of solvent species when they are present in high concentrations and, simultaneously, water is depleted in the solution. For example, the best fit for the HNO 3 þ H 2 O system was obtained when the parameters These parameters are listed in Table 3.…”