Transference Number Data Research Articles

Ion‐Solvent Interactions of Silver (I) Salts in Water‐DMSO Mixtures from Conductance Measurements

AbstractThe conductances of silver (I) perchlorate, nitrate and bromate have been determined in water‐dimethylsulfoxide (DMSO) mixtures at 30°C over the complete range of solvent compositions. The data were analyzed by the 1980 Fuoss equation and the limiting molar conductances (<Λ0) and association constants (KA) of the salts were evaluated at all compositions. The Λ0 values have been split into their ionic values and the ionic Walden products of all the ions were calculated using the transference number data derived from a concentration cell with transference. The initial increase of the Walden product of silver ion up to 20 wt% DMSO and its subsequent decrease beyond this composition with addition of DMSO, indicates that it is preferentially solvated by water at high compositions of water and subsequently by DMSO. For anions, the Walden products vary in a complex manner and seem to be strongly influenced by solvent‐solvent interactions.

Transport mechanisms in iontophoresis. I. A theoretical model for the effect of electroosmotic flow on flux enhancement in transdermal iontophoresis.

Bulk fluid flow or volume flow in the direction of counterion flow is a probable mechanism for enhanced flux of uncharged species by iontophoresis. Both the electrical volume force effect, resulting from the interaction of the "ion atmosphere" and the electric field, and an induced osmotic pressure effect produce volume flow in the same direction as counterion flow through the membrane. Since each of these effects is proportional to the membrane charge and the imposed electric field, we classify both as electroosmotic flow. This research develops a detailed theoretical model which allows the effect of volume flow on flux enhancement to be evaluated. A detailed theoretical result for the electroosmotic flow coefficient also results from the analysis. The model assumes that transport occurs in three types of aqueous pores: positively charged, neutral, and negatively charged. For hairless mouse skin (HMS), pore size, charge, and number are evaluated from transference number, volume flow, and electrical resistance data. The flux enhancement ratio is J1/J1D = sigma Ai alpha i/[1-exp(-alpha i)], where i = pore type, and the summation runs over the three pore types. Ai is the area fraction of pore type i effective for transport; J1 and J1D are flux of species 1 with and without the electric field, respectively; and alpha i is given by alpha i = F(-delta phi/RT)[zeta 1 + (-zeta mi)Bari2Cmi(Gi + F)].(ABSTRACT TRUNCATED AT 250 WORDS)

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

Mutual diffusion coefficients were measured at 298.15 K for aqueous mixtures of with at concentrations of 0.5, 1.25, 2.0, and 4.0 mol‐dm−3, using Rayleigh interferometry. These systems correspond to a fully charged zinc‐chlorine storage battery at various supporting electrolyte concentrations. The main term diffusion coefficient is nearly independent of concentration, whereas the main term varies by one‐third. The cross term is small and positive. The cross term varies from moderately large and positive to quite large and negative as the concentration increases. The experimental values cannot be reliably approximated by Nernst‐Hartley type equations, even with speciation assumptions. Mutual diffusion data, together with transference number and conductivity data (when available), can be used to calculate ion transport in systems with combined electrical and diffusive transport.

Technique for measurement of transference numbers in membranes involving minimal concentration changes : Application to cellophane in potassium hydroxide solutions

True transference numbers may be determined by measuring the quantities of ions and solvent transported across a membrane on passing an electric current. In most previous work concentrations on one or both sides of the membrane have been allowed to change during the run. Ideally, the concentrations should be maintained invariant during the electrolysis to minimise transfer of solvent and solute by osmosis and diffusion, respectively. The maintenance of constant concentrations may also be important if the membrane characteristics show irreversibility on changing concentrations as is found with Cellophane in alkaline solutions. In the present paper a technique is described for holding solution compositions constant requiring only relatively simple equipment. Reversible electrodes are not essential and the method allows determination of both ionic and solvent transference numbers simultaneously. The cell described is rapid to assemble and an excellent membrane-cell seal is obtained eliminating solution leakage. Transference number data for Cellophane in potassium hydroxide solutions covering a wide concentration range, determined using the technique described, are presented.

Isothermal transport properties in solutions of symmetrical tetra-alkylammonium bromides

Density, molar conductance, transference number, tracer diffusion (cation, anion, water) and mutual diffusion data are reported for aqueous solutions of the following symmetrical tetra-alkylammonium halides at 25 °C up to 2 mol kg–1 concentration: Me4NBr, Et4NBr, n-Pr4NBr and n-Bu4NBr. These data were used to obtain information on the interactions between pairs of species c, a, w (cation, anion, water) using Hertz's velocity-correlation formalism. Within this formalism the transport coefficients are related to time integrals over velocity cross-correlation functions between the various interaction partners. Results obtained for solutions of tetra-alkylammonium salts differ characteristically from those reported for alkali halides and reflect structural features such as hydrophobic hydration, cation–cation and anion–anion interactions.

Single-ion and molar conductances. Application to transference number data analysis

Several of the present molar conductance equations have been examined in detail in order to obtain equations for the concentration dependence of the single-ion conductances which, when combined with existing conductance and transference data, permit three independent evaluations of the conductance parameters, in particular the association constant and the distance of closest approach of two ions of opposite charge. In order to make use of existing transference data it was necessary to develop a suitable extrapolation equation. It is shown that the procedures outlined constitute a useful test of the concentration dependence of transference numbers found experimentally.

Density, conductance, transference numbers, and diffusion measurements in concentrated solutions of nickel chloride at 25�C

The Hittorf technique for measuring transference numbers has been modified to produce precise data in concentrated aqueous electrolyte solutions. Density, molar conductance, transference number, tracer-diffusion, and mutual diffusion data are reported for aqueous NiCl2 solutions up to 4M concentration at 25°C.

Spherical lipid bilayer membranes: Electrical and isotopic studies of ion permeability

The permeability of spherical lipid bilayer membranes (Pagano &, Thompson, 1967 a,b) to sodium and chloride has been determined by direct measurement of isotopic fluxes and by calculation from the electrical parameters of this system. These membranes were generated in an aqueous sucrose density-gradient which was 0.2 m in NaCl, and were formed from a solution of egg phosphatidyl choline and n-tetradecane in chloroform-methanol. Using 22Na and 36Cl, the unidirectional fluxes M Na and M Cl were found to be respectively 0.39 ± 0.02 and 90.2 ± 0.8 μμmoles/cm 2/sec at 30°C °C, giving a value of M Na M Cl = 0.0043 . A plot of ln M Cl versus T −1 was linear over the temperature range 10 to 30 °C, and yielded a value of 10.7 ± 0.4 kcal./mole for the activation energy for chloride permeation. The corresponding activation energy for sodium was not determined. Following the treatment of Hodgkin (Hodgkin, 1951), values of less than 2.0 μμmoles/cm 2/sec for these fluxes were calculated from the electrical conductance and transference number data for this system. On the basis of the electrical transference data, the ratio M Na M Cl was expected to be about 4.9. The isotopic chloride flux was examined in detail and shown to exhibit saturation kinetics. The difference between this flux and the value calculated from the electrical parameters may thus be accounted for by assuming the existence of an auxiliary carrier-mediated diffusion mechanism for chloride permeation.

Origin of the Electric Potential Observed in Wells

Abstract The mechanism by which an electrical potential difference is developed between two salt solutions separated by shale is shown to be a consequence of the electrical double layer of the shale surfaces. A mathematical derivation is presented to show the dependence of the potential on the shale characteristics and on the concentration of the salt solutions. The equations developed describe adequately the potential-concentration behavior of a long shale core. The equations also describe the variation of potential of sand-shale mixtures with variation of clay content. Ion adsorption is an important factor in the development of the surface charge on the shale, and electrical resistivity and ion transference number data are employed to estimate the increase of surface charge with concentration. Since the potential is shown to be dependent on the characteristics of the particular system, water salinities estimated from the potential log by previously proposed methods may be low in some cases. Introduction That the electric well log exists today may be attributed to the ingenuity of the Schlumberger brothers, who adapted to the logging of wells techniques which were originally developed as surface prospecting methods for the location of ore bodies. Empirically, it was found that the potential curve of the electric log usually gave values for clean sands which were negative with respect to the values for shales. It was suggested that the potential was responsive to porosity. It was postulated, in explanation, that the potential was the sum of a streaming potential, which differed for sands and shales, and of an "electro-chemical" potential of undetermined origin. Mounce and Rust in 1943 showed that the streaming potential is small in most cases and that the potential is generated by a process in which shale and a salinity difference play essential parts. Dickey, in the same year, concluded that the potential is dependent upon adsorptive properties of reservoir rock.