J. Phys. II France
Volume 6, Numéro 11, November 1996
Page(s) 1571 - 1583
DOI: 10.1051/jp2:1996148
J. Phys. II France 6 (1996) 1571-1583

Tracer Diffusion of 65Zn 2+ in Binary Isobutyric Acid + Water Mixtures Near the Critical Point

Moncef Bouanz

Laboratoire de Diffusion, Département de Physique, Faculté des Sciences de Tunis, 1060 Tunis, Tunisia

(Received 20 November 1995, revised 20 May 1996, accepted 1 August 1996)

Tracer diffusion coefficients of 65Zn 2+ in mixtures of isobutyric acid water and 10-4 M ZnCl 2 have been measured over the composition range $0 < X < 95\%$ in acid; at $\theta_1 = T_1 -T_{\rm c} = 0.547$ K and $\theta_2 = T_2 - T_{\rm c} = 7.547$ K using the open-ended capillary method. The critical temperature was found to be: $T_{\rm c} = 27.453~^\circ$C. An important anomaly was detected in the neighbourhood of the critical point $X_{\rm c} = 0.38$, X being the weight percentage of the acid. The concentration dependence as the shear viscosity coefficients were evaluated at each X value for the same temperatures. The results are discussed in terms of Einstein-Stokes law. Our analysis suggests three different behaviours of the diffusing entity in the mixtures and it is based on the preferential solvation phenomenon.

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