Mutual Diffusion Coefficients of ZnCl₂-H₂O at 298.15 K by Rayleigh Interferometry

Abstract

Zinc chloride / Aqueous solutions / Diffusion coefficientsVolume fixed mutual diffusion coefficients have been measured for aqueous ZnCl2 solutions from 0.005 to 5.652 mol • dm"3 at 298.15 K using free-diffusion Rayleigh interferometry. Most experiments were for stoichiometric high purity solutions, but solutions with either a 0.14% excess or several hundredths of a percent deficiency of HC1 were also investigated. These minor deviations from stoichiometry had no detectable effect on the diffusion coefficients; thus hydrolysis does not affect the results. The ZnCl2 diffusion coefficients exhibit a shoulder around 0.2 mol • dm"3 that may be due to selfcomplexing. Other workers have reported related anomalies in tracer diffusion coefficients of the H20, in viscosities, and in activity coefficient derivatives of ZnCl2 solutions.These anomalies appear to be characteristic of and limited to zinc halide solutions. Two commercial sources of ZnCl2 were found to contain large amounts of alkali metal and alkaline earth metal impurities; these impurities raise the diffusion coefficients but have little effect on the anomaly. Thermodynamic diffusion coefficients were calculated for ZnCl2 solutions and compared to similar data for other 2-1 chlorides; of the salts studied so far, ZnCl2 is unique with its double maxima. Wir haben mit Hilfe der Rayleigh-Interferometrie den Diffusionskoeffizienten fiir wiiBrige Zinklosungen (0,005 -5,652 mol • dm"3) bei 298,15 K gemessen. Die Mehrzahl der Experimente wurde mit reinen, stochiometrischen Losungen durchgefuhrt; in einigen Experimenten haben wir aber auch Losungen benutzt, in denen der Gehalt an HC1 entweder 0,14% oberhalb oder einige Hundertstel Prozent unterhalb der Stochiometrie lag. Diese kleinen Abweichungen von der Stochiometrie hatten keinen meBbaren EinfluB auf die Diffusionskoeffizienten, woraus zu schlieBen ist, daB die Hydrolyse die Ergebnisse nicht beeinfluBt. Die Diffusionskoeffizienten zeigen eine Schulter bei etwa 0,2 mol dm "3, die eine Folge von Komplexbildung sein mag. Andere Forscher haben verwandte Anomalien in Tracerdiffusionskoeffizienten, in Viskositiiten und in GroBen, die sich vom Aktivitatskoeffizienten ableiten, bei ZnCl2-L6sungen gefunden. Diese Anomalien scheinen charakteristisch fiir uns begrenzt auf Zinkhalid-Losungen zu sein. ZnCl2 von zwei kommerziellen Lieferanten enthielt groBe Mengen von Alkali-Metall-und AlkaliErdmetall-Unreinheiten. Diese Unreinheiten erhohen den Diffusionskoeffizienten, aber haben kaum einen EinfluB auf die oben genannte Anomalie. Wir haben die thermodynamischen Diffusionskoeffizienten fiir ZnCl2-L6sungen berechnet und sie mit ahnlichen Brought to you by | New York University Bobst Library Technical Servi Authenticated Download Date | 6/12/15 6:43 AM142 J. A. Rard and D. G. MillerDaten fur andere 2-1-Chloride verglichen; unter alien Salzen die bisher studiert wurden ist ZnCl2 mit seinem Doppel-maximum einmalig.

Isothermal transport coefficients in concentrated aqueous solutions of unsymmetrical electrolytes: lanthanum trichloride at 25.degree.C

“…Curves for sulfates28,53 and associating transition-metal salts54•55 show a different behavior, although in some cases the typical form for unassociated electrolytes is qualitatively retained. 55 Clearly, there is a very subtle dependence of Z)v on the extent and type of ion association. As is seen from Figure 3, Z)v in aqueous LaCl3 follows the general pattern, the results being very similar to those obtained for MgCl252 and CaCl248 which are also displayed in Figure 3.…”

Osmotic and Activity Coefficients of the {xZnCl2+(1−x)ZnSO4}(aq) System at 298.15 K

“…The rather large variation in the values of that were attributed to the sudden onset of complex formation [7,[37][38][39], and that the Hittorf transport numbers for Zn(II) becoming negative above 2.0 mol·kg -1 was attributed to the formation of negatively changed zinc-chloro complexes [17,19]. There is more direct evidence for the nature of these complexes that will now be described.…”

Mutual Diffusion Coefficients of Various ZnCl2 ( 0.5M ) ‐ KCl ‐ H 2 O Mixtures at 298.15 K by Rayleigh Interferometry

“…Because this stock was used only with the 2M KCI concentration, the effect of these impurities on diffusion is not large. Indeed the effect is about 0.5% in the binary solution (10). However, impurities do reduce the densities.…”

“…These expectations were generally borne out by experiment.There are existing literature diffusion data at 25~ for KC1-H20 (5-8) and ZnCI~-H20 (9). We previously extended the data for KC1-H20 (8), and recently reinvestigated ZnC12-H20 with higher precision and to lower and higher concentrations (10).In this paper we present the multicomponent diffusion coefficients, determined optically, for ZnC12-KC1-H20 with ZnC12 at 0.5M and KC1 at 0.5, 1.25, 2.0 and 4.0M, where M refers to the molarity in mol-dm -3. This ZnC12 eoncentra-…”

“…There are existing literature diffusion data at 25~ for KC1-H20 (5-8) and ZnCI~-H20 (9). We previously extended the data for KC1-H20 (8), and recently reinvestigated ZnC12-H20 with higher precision and to lower and higher concentrations (10).…”