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1.
The activation energy for the diffusion of ZnSO4 as a function of electrolyte concentration is computed by least squares fitting of the diffusion coefficient data obtained at various temperatures in the Arrhenius equation. It is observed that the activation energy decreases with increasing concentration of the electrolyte. This observation is accounted for on the basis of Wang's model. Further, the obstruction effect caused by the agar macromolecules in the diffusion path of ZnSO4 uis also determined at these concentrations by varying the gel concentration at 25°C., The obstruction effect expressed in terms of a found to decrease with ZnSO4 concentration and explained on the basis of competitive hydration of diffusing ions and agar molecules.  相似文献   

2.
The obstruction effect and activation enerqy for the self-diffusion of Co2+ ions in CoSO4 have been computed using the zone-diffusion technique in agar gel medium at five different concentrations of the electrolyte. Both parameters are found to decrease with an increase in electrolyte concentration. The decrease in obstruction effect expressed in terms of is attributed to the competitive hydration between ions and agar molecules in a diffusion system while the decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level.  相似文献   

3.
The obstruction effect for tracer-diffusion of Mn2+ ions in the presence of different supporting electrolytes (LiCl, NaCl, KCl, CsCl) at various concentrations has been studied at 25 °C using the zone diffusion technique. It has been observed that the obstruction effect determined in terms of increases with concentration of the electrolyte. Further, for a given concentration it is found to decrease with increasing charge density of the cation. We also report here on the effect of temperature on obstruction and found that is constant over the temperature range studied (25–45 °C). These observations are explained on the basis of competitive hydration between ions and agar macromolecules.  相似文献   

4.
The activation energy for the tracer diffusion of Co2+ ions in multielectrolyte systems containing alkali bromides has been determined in agar gel medium over the temperature range of 25–45°C. The decrease in the value of the Arrhenius parameters, E and Do, with gel percentage is explained on the basis of the transition state theory. Further, studies of the influence of electrolyte concentration on activation energy and obstruction effect reveal that both parameters decrease with the former. The decrease in activation energy is explained by considering the changes in physical properties of the solution with concentration at microscopic level, while the decrease in the extent of obstruction effect is attributed to competitive hydration between ions and agar molecules in a diffusion system.  相似文献   

5.
Tracer-diffusion of Zn2+ ions in the presence of CoSO4 is studied at 25°C in 1% agar gel over a concentration range of 10–5 to 0.25M using a zone-diffusion technique. The deviations observed between experimental and theoretical values of diffusion coefficients are explained by considering different types of interactions occurring in the ion-gel-water system. Further, study of the obstruction, effect in the diffusion of Zn2+ ions at different concentrations of CoSO4 reveals that the -value decreases with increasing concentration of the electrolyte. This observation is accounted on the basis of competitive hydration between ions and agar molecules.  相似文献   

6.
Tracer diffusion of131I ions is studied at different temperatures /20°C–50°C/ in 2.5% agar gel containing sodium and potassium sulphate solutions over a wide range of concentrations. The results are in qualitative agreement with the theoretical values in the concentration range 10–6–10–1M. Agar gel shows an obstruction effect to diffusional flow. The activation energy for tracer diffusion was found to be of the order of 16.3 kJ mol–1.  相似文献   

7.
Multitracer technique and -ray energy spectrum analysis was used to study the effect of Ag+ on the uptake of some tracer metal ions in the somatic embryogenesis of Lycium barbarum L. The results show that in the case of some metal ions the uptake changes are selective, cooperative and interactive in somatic embryogenesis due to Ag+ influence. To 50 mg/l Ag+ concentration, the uptake and the frequency of somatic embryogenesis increases along with increasing concentration. Ag+ could speed up cell differentiation and somatic embryogenesis. Above 50 mg/l Ag+ concentration, Ag+ has a poisonous effect, influences tracer element absorption and inhibit the frequency of somatic embryogenesis.  相似文献   

8.
The present paper gives an account of different aspects of the tracer diffusion of Cs+ ions in alkali metal bromides. We have measured the diffusion coefficients, D, of cesium ions in 1% agar gel medium at 25 C using a zone-diffusion technique over a concentration range of 5 × 10−5 to 0.1 mol,dm−3. The values of the diffusion coefficients were found to deviate from theory, which are explained on the basis of different types of interactions occurring in the ion-gel-water system. The study is also focused on the effect of alkali metal bromides on the obstruction effect and activation energy for the tracer-diffusion of cesium ions in agar gel medium. It is observed that both parameters, extent of obstruction, ∝, and activation energy, E, decrease with increasing charge density of the cation of the supporting electrolyte. The influence of these trends is explained on the basis of competitive hydration between the ions and agar molecules, and the relative distortion in the water structure that is brought about by these different ions and agar molecules.  相似文献   

9.
A simple and absolute closed capillary method is introduced for measuring tracer diffusion coefficients in liquids with both - and -active tracers. In this method a narrow capillary is partially filled with a labelled solution and an unlabelled solution is used to fill the rest of the capillary. The diffusion coefficient is obtained from the time dependence of the monitored activity when the length of the capillary is known. The method has been tested by remeasuring the tracer diffusion coefficients of22NaCl and Na36Cl for solutions covering a wide range of total NaCl concentration. The average precision of the measurements was about 0.3%. The results obtained for Na36Cl tracer diffusion are in good agreement with the data found in literature. The22NaCl tracer diffusion coefficients that were measured in dilute solutions agree well with those obtained using the continuous open-ended capillary method but differ from results for solutions between 0.1 and 1M obtained with the diaphragm cell method.  相似文献   

10.
Variation of activation energy for tracer-diffusion of Co2+ ions in Ni(NO3)2, Co(NO3)2 and Mn(NO3)2 is investigated using 1% agar gel over the temperature range of 25 to 45 °C. The activation energies are obtained by the least square fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots. Further, the extent of obstruction effect by gel macromolecules for Co2+ ions in Ni(NO3)2, Co(NO3)2 and Mn(NO3)2 systems at various concentrations of the electrolyte have been determined. The decrease in activation energy is explained by considering the changes in the physical properties of the solution with concentration at microscopic level, while the decrease in obstruction effect expressed in terms of a is accounted for on the basis of competitive hydration between ions and agar molecule.  相似文献   

11.
The effect of some alkali metal chlorides on obstruction effect // and activation energy /E/ for the tracer-diffusion of cobalt ions is studied in agar gel medium using the zone-diffusion technique. It is observed that both the parameters, and E, decrease with increasing charge density of cation of the supporting electrolyte. This trend is explained on the basis of competitive hydration between ions and agar molecules and the relative distortion in the water structure brought about by these different ions and agar molecules, respectively.  相似文献   

12.
Nernst—Planck equations and ionic conductivities are used to calculate accurate limiting interdiffusion coefficients D ik o for mixed electrolyte solutions. The electrostatic mechanism for coupled electrolyte diffusion is investigated by calculating the electrostatic contribution to each D ik o coefficient to give the flux of each electrolyte driven by the electric field, which is generated by the migration of ions of different mobilities. Ternary diffusion coefficients are measured for dilute aqueous K2SO4 + KOH and Li2SO4 + LiOH solutions. Because of the different mobilities of K+ and Li+ ions relative to SO 4 2– ions, diffusing K2SO4 drives cocurrent flows of KOH, but diffusing Li2SO4 drives counterflows of LiOH. To describe coupled diffusion in concentrated mixed electrolyte solutions, the Hartley–Crank theory is used to correct the limiting D ik o coefficients for nonideal solution behavior, viscosity changes, ionic hydration, and the zero-volume flow constraint. Diffusion coefficients predicted for concentrated aqueous CaCl2 + HCl solutions are compared with recently reported data. The large amount of HCl cotransported by the diffusing CaCl2 is attributed to the salting out of HCl by CaCl2 and to the migration of H+ ions in the diffusion-induced electric field, which slows down the Cl ions and speeds up the less-mobile Ca2+ ions to maintain electroneutrality along the CaCl2 gradient.  相似文献   

13.
The features of formation of hydration spheres around electrolyte ions in aqueous solutions of sodium nitrate and thiosulfate in a wide concentration range (from 2 to 42 wt %) at temperatures from 278.15 to 318.15 K were determined from the isoentropy compressibility data. The structural characteristics of the solute hydration complexes were determined. The hydration numbers decrease with increasing concentration and are independent of temperature. Na2S2O3 has the highest hydration number at infinite dilution (h 0) and is characterized by the lowest molar isoentropy compressibility of water in the hydration spheres of the ions (S,1hV1h). Sodium thiosulfate, compared to sodium nitrate, interacts with water stronger, and its aqueous solutions show a greater degree of ordering.  相似文献   

14.
Formation of Liesegang rings on the growth of BaMoO4 crystals in silica gel by single diffusion is discussed. The rhythmic precipitation is found to be influenced profoundly by (a) the molarity of inner and outerelectrolytes (b) the age of gel and (c) the pH of the gel medium. The time law, spacing law and the law relating diffusion depth and width are verified. A method to estimate the diffusion coefficient of the outer electrolyte in the gel medium is developed and calculated for Ba++ions.  相似文献   

15.
Tracer and self-diffusion coefficients for Rosebengal labelled with131I are determined in agar gel medium at different temperatures and the activation energies for the two processes are determined by zone diffusion technique. The slight difference in tracer and self-diffusion values observed is small enough to be consistent with Hertz's recent theory of linear response of tracer diffusion coefficients in electrolyte and non-electrolyte systems.  相似文献   

16.
The values of activation energy required for the diffusion of ZnCl2 and for Cd2+ ions in Cd/Ac/2 are reported in agar gel medium at 5×10–5 and 0.001M concentration, respectively. These values are compared with the previously reported values in the same systems at different concentrations. The decrease in activation energy with concentration of electrolyte is in agreement with the Wang's model.  相似文献   

17.
Heats of solution of 13 11 electrolytes in 1-propanol have been determined calorimetrically at various electrolyte concentrations, and extrapolated to zero concentration to give H s o values for these electrolytes. Together with literature data on three additional 11 electrolytes, these measurements yield a self-consistent set of single-ion enthalpies of transfer from water to 1-propanol. Values are tabulated for 10 univalent cations and five univalent anions. It is shown that the H t o (Ph 4 As+)=H t o (Ph 4 B) assumption yields chemically reasonable single-ion values. Using this assumption, it may be deduced that all the univalent ions studied have about the same enthalpy in 1-propanol as in methanol.  相似文献   

18.
Tracer-diffusion of Co2+ ions is studied in agar gel in the presence of sodium and potassium nitrates at 25°C. The diffusion coefficient values at various electrolyte concentrations are compared with the corresponding theoretical values computed on the basis of Onsager's theory. The deviations from the theory are attributed to the various co-occurring effects in the diffusion medium. The activation energy for the process of diffusion of Co2+ ions in presence of above electrolytes is also reported.  相似文献   

19.
Tracer diffusion coefficients of cobalt ions have been measured in the supporting medium containing multi-electrolyte systems of alkali bromides. The electrolyte concentration was varied between 10–6-0.1M at 25°C and the diffusion coefficients were determined by zone-diffusion technique using agar gel medium. The trend in the theoretical values of diffusion coefficients is accounted for by considering the relative contribution of mobility function, ionic strength as well as ion size parameter to the theoretical value in different systems. While the deviations between theoretical and experimental values of diffusion coefficients are explained on the basis of various co-occurring effects in ion-gel-water system.  相似文献   

20.
Organic–inorganic composite mono-valent cation selective membranes (MCSMs) were prepared by sol–gel under acidic conditions, in which sulfonic acid groups were introduced at the inorganic segment. Studies on physicochemical and electrochemical properties revealed their excellent mechanical, thermal, and oxidative stabilities, high conductivity, ion-exchange capacity, permselectivity for mono-valent cations, ionic diffusion and water transport number. These properties suggested the suitability of MCSMs, especially Si-65%, for electro-separation of Na+ from Ca2+, Mg2+, and Fe3+. The effect of electrolyte solution on the characteristics of the current–voltage (iv) curve in MCSM was studied based on the concentration polarization. Electro-transport of different ions in terms of plateau length and concentration profiles for different ions in the solution phase, diffusion boundary layer and membrane phase were presented. Information obtained from iv curve analysis were validated by electrodialysis (ED) experiments for individual or mixed electrolyte solutions. Electro-transport efficiency and separation factor of different ions for MCSM and Nafion117 (N117) membranes were compared, which suggested suitability of MCSMs for separating cations.  相似文献   

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