This paper presents the experimentally determined precise transport data - (tracer) diffusion coefficients in both water and heavy-water environments, together with molar conductivity and viscosity of (ortho)phosphoric acid in water over an extended concentration range at [Formula: see text]. The concentration (c) dependence of the diffusion coefficients (D), viscosity [Formula: see text] and molar conductivity [Formula: see text] have been analysed. An anomalous depression in the D - [Formula: see text] curve for both [Formula: see text] - [Formula: see text] and [Formula: see text] - [Formula: see text] systems in the neighbourhood of 0.8 M is observed, which is complementary to the sudden sharp rise observed in the [Formula: see text] curve in the neighbourhood of 0.8 M. Although the occurrence of such an anomaly could be inferred from the earlier conductance, e.m.f. and diffusion data, it was never conclusively inferred earlier. This new set of diffusion and viscosity data clearly delineates anomalies in the ion transport of phosphoric acid.

The existence of isotope effect in liquid diffusion is thoroughly investigated in aqueous solutions of NaCl and CsCl. The tracer difFusion coefFicients with difFerent isotopes of the same species are measured by the sliding-cell technique. The experimental data shower strong evidence of the existence of an isotope efFect in the difFusion of a NaCl and CsCl solution.The phenomenon of diffusion, a fundamental rate process occurring in every physicochemical reaction, is a subject of great topical interest. There is a well-known controversy about the existence of the isotope effect in liquid diffusion and still today it is not known whether this effect can be neglected or not. Many experimental investigations were carried out in this field, but none of them could provide conclusive evidence in favor of the isotope effect. The radioactive tracer technique is one of the sensitive tools which involves the use of isotopically labeled radioactive species for the measurement of the diffusion coeKcients in liquids. If the isotope effect has any contribution, the mass change due to the labeling of the molecules with suitable radioactive isotopes will cause the measured tracer diffusion coefFicient to differ from the true self-diffusion coefFicient. This aspect needs a thorough investigation with different liquid systems. We chose the aqueous solution of the two most interesting binary electrolytes, NaCl and CsCl, in one of which the cations (Na) has a structure-forming capacity and other (Cs) has a structure-breaking capacity. This enables us to study the isotope effect in binary electrolytes of opposite cationic properties. An appreciable difference in the tracer diffusion coefFicients of different isotopes for the same system at the same concentration is found which provides strong evidence for the existence of the isotope effect in the diffusion of aqueous NaCl and CsCl.A critical survey through the literature about previous studies on the isotope effect reveals that Miller's work of isotopic separation of lithium isotopes by diffusion in an aqueous solution leads to the conclusion that the lighter isotope ( Li) diffuses more rapidly than the heavier isotope ( Li). The observation is congruent with the findings of some other groups from their work on liquid Li and Li. The ratios of the self-diffusivities of Li and Li are found to be significantly greater than the square root of the inverse mass ratio. Feinauer et Ol. have parametrized the isotope effect from diffusivity studies on Li and Li. Their values are compatible with the ratio of self-diffusivities of Li and "Li as obtained from a quantum mechanical calculation by Omini based on the pseudopotential method. Pikal studied the diffusion coefficient ratio of the ions Na and Na in a 0.1M NaCl solution and found that the lighter isotope diffused slightly more rapidly than the heavier one, the ratio of the diffusion coefFicient of Na to Na being 1.002. He also found that the ratio to be 1.004 for sodium diffusion in 10M LiBr solution. These works show (Dt -Dh) Conc.

A realistic model to study the properties of an aqueous electrolyte surface has been developed. The complex liquid surface consisting of a large number of interacting particles, ions and dipoles, is modelled using a Monte Carlo technique considering grand canonical sampling. The possible interactions existing in the system are charge-charge, charge-dipole, chargequadrupole and dipole-dipole. The concentration dependence of the diffusion coefficient suggests a first order phase transition (structural transition), while its temperature dependence indicates the existence of a second order phase transition. A critical analysis of the effect of decreasing temperature on the samples with added cations to limit motion of the particles in the surface reveals an interesting feature-a signature of glass transition.

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