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A simple apparatus for the measurement of colligative properties in aqueous electrolyte systems: an educational approach

Pinho, Simão; Macedo, Eugénia A.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
722.1352%
The importance of systems with electrolytes is well known nowadays, and many examples can be given about their industrial applications. However, at undergraduate level the properties of electrolyte solutions are neither theoretically nor experimental]y focused in accordance to the role they play in chemical industry. In this work simple equipment for the measurement of freezing point depression due to the presence of strong electrolytes in water is introduced. A study with the salts NaCI and XCI in the molality range up to 4 molal is suggested. In this way, the students may gain some insight on the physical-chemistry of aqueous electrolyte solutions. The experimental data are compared with the values obtained from available models to calculate the activity coefficients of the salts and water activities, mainly those concerned with the Debye-Hückel equation and its empirical extensions. It is also suggested to use those equations and the data to model the freezing point depression at high electrolyte concentrations.

Partial molar volumes of amino acids in aqueous MgSO4 solutions between 278.15 and 308.15 K

Mota, Ana Carolina Costa
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Dissertação de Mestrado
ENG
Relevância na Pesquisa
511.434%
The main objective of this work is to contribute to the understanding of the molecular interactions between ions and protein groups in aqueous solutions, using amino acids as model compounds, by determining the partial molar volumes of glycine, L-alanine, DL-2-aminobutyric acid and L-valine in aqueous magnesium sulphate solutions. The densities of aqueous solutions of magnesium sulphate (0.1, 0.3, 0.7 and 1.0) mol·kg-1 containing the selected amino acids were measured at (278.15, 288.15, 298.15 and 308.15) K, using a digital density meter. After, the partial molar volumes at infinite di-lution of the amino acids were calculated, and then used to obtain the corresponding transfer volumes and hydration numbers. The dehydration effect on the studied amino acids was observed, increasing temperature or salt molality. The positive values of ∆trVmA suggest that the interactions ion/hydrophilic group (zwitterionic centers) are predominant, and applying the method-ology proposed by Friedman and Krishnan (1973), it was concluded that they are main-ly pairwise. Regarding the alkyl chain effect, the increase of the hydrophobic part of amino acids (glycine > L-alanine > DL-2-aminobutyric > L-valine) does not result in a decreasing trend of the partial molar volumes of transfer. To further analyse the alkyl chain effect of the amino acids...

The electrochemical behaviour of Ti-13Nb-13Zr alloy in various solutions

ASSIS, S. L.; WOLYNEC, S.; COSTA, I.
Fonte: WILEY-V C H VERLAG GMBH Publicador: WILEY-V C H VERLAG GMBH
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
511.62312%
The electrochemical behaviour of a near-beta Ti-13Nb-13Zr alloy for the application as implants was investigated in various solutions. The electrolytes used were 0.9 wt% NaCl solution, Hanks` solution and a culture medium known as minimum essential medium (MEM) composed of salts, vitamins and amino acids, all at 37 degrees C. The electrochemical behaviour was investigated by the following electrochemical techniques: open circuit potential measurements as a function of time, electrochemical impedance spectroscopy (EIS) and determination of polarisation curves. The obtained results showed that the Ti alloy was passive in all electrolytes. The EIS results were analysed using an equivalent electrical circuit representing a duplex structure oxide layer, composed of an inner barrier layer, mainly responsible for the alloy corrosion resistance, and an outer and porous layer that has been associated to osteointegration ability. The properties of both layers were dependent on the electrolyte used. The results suggested that the thickest porous layer is formed in the MEM solution whereas the impedance of the barrier layer formed in this solution was the lowest among the electrolytes used. The polarisation curves showed a current increase at potentials around 1300 mV versus saturated calomel electrode (SCE)...

An extension of the Pitzer equation for the excess Gibbs energy of aqueous electrolyte systems to aqueous polyelectrolyte solutions

PESSOA FILHO, Pedro de Alcantara; MAURER, Gerd
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
516.42008%
Pitzer`s equation for the excess Gibbs energy of aqueous solutions of low-molecular electrolytes is extended to aqueous solutions of polyelectrolytes. The model retains the original form of Pitzer`s model (combining a long-range term, based on the Debye-Huckel equation, with a short-range term similar to the virial equation where the second osmotic virial coefficient depends on the ionic strength). The extension consists of two parts: at first, it is assumed that a constant fraction of the monomer units of the polyelectrolyte is dissociated, i.e., that fraction does not depend on the concentration of the polyelectrolyte, and at second, a modified expression for the ionic strength (wherein each charged monomer group is taken into account individually) is introduced. This modification is to account for the presence of charged polyelectrolyte chains, which cannot be regarded as punctual charges. The resulting equation was used to correlate osmotic coefficient data of aqueous solutions of a single polyelectrolyte as well as of binary mixtures of a single polyelectrolyte and a salt with low-molecular weight. It was additionally applied to correlate liquid-liquid equilibrium data of some aqueous two-phase systems that might form when a polyelectrolyte and another hydrophilic but neutral polymer are simultaneously dissolved in water. A good agreement between the experimental data and the correlation result is observed for all investigated systems. (c) 2008 Elsevier B.V. All rights reserved.

Formation of SnO2 gels from dispersed sols in aqueous colloidal solutions

Satoshi Hiratsuka, Renato; Helena Pulcinelli, Sandra; Valentim Santilli, Celso
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 76-83
ENG
Relevância na Pesquisa
609.066%
Transparent SnO2 gels were obtained from SnCl4 aqueous solution. The sol formation from tin oxihydroxy peptization in different concentrations and by electrolyte addition in solution was measured. It was verified that the residual presence of chloride ions compromises the colloidal system stability. The sol-gel transition was investigated as a function of the quantity of solid particles in the aqueous environment and of aging time at 60°C by infrared spectroscopy and rheological measurements. The transition from plastic to pseudoplastic flow observed with the increase in loading suggests that a continuous and three-dimensional network formation is closely related to hydrogen bridges and/or hydrogen clusters, culminating in the gel formation. © 1990.

Direct measurement of the interaction between phosphatidylglycerol bilayers in aqueous electrolyte solutions.

Marra, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1986 EN
Relevância na Pesquisa
606.77383%
Results are presented of force measurements between deposited bilayers of dimyristoylphosphatidyl glycerol (DMPG) at T greater than Tm, and distearoylphosphatidyl glycerol (DSPG) at T less than Tm. Below a bilayer separation of 100 nm, a repulsive double-layer force is measured, which can be explained through the combined screening and binding effect of the counterions in electrolyte solutions of NaCl, HCl, CaCl2, or mixtures of these. The binding of cations to bilayers in the fluid phase (DMPG) appears to be greater than to bilayers in the gel phase (DSPG). At shorter range, below approximately 3 nm, an attractive interaction is measured in solutions containing CaCl2, which was found to be slightly stronger than the theoretically expected van der Waals interaction. No hydration force was observed to exist in solutions containing CaCl2. In NaCl solutions, the measured interbilayer force can completely be accounted for by the electrostatic repulsion, down to a bilayer separation of at least 2 nm, below which no accurate measurements were possible anymore. Parallel measurements on PG monolayers show that the contraction of a DMPG monolayer following addition of CaCl2 is significantly greater than what is predicted from the change in the double-layer free energy alone. This indicates that changes in the lateral interactions between the lipid headgroups probably involve Ca2+-bridge binding and/or a possible dehydration of the lipid headgroups through Ca2+ binding. The results shed new light on both the interbilayer and intrabilayer interactions of PG and identify the possible factors responsible for the morphological behavior of PG aggregates.

General electrokinetic model for concentrated suspensions in aqueous electrolyte solutions: electrophoretic mobility and electrical conductivity in static electric fields

Carrique Fern??ndez, F??lix; Ruiz-Reina, Emilio; Roa, Rafael; Arroyo Rold??n, Francisco J.; Delgado, ??ngel V.
Fonte: Elsevier Publicador: Elsevier
Tipo: Pré-impressão
ENG
Relevância na Pesquisa
1036.7969%
In recent years different electrokinetic cell models for concentrated colloidal suspensions in aqueous electrolyte solutions have been developed. They share some of its premises with the standard electrokinetic model for dilute colloidal suspensions, in particular, neglecting both the specific role of the so-called added counterions (i.e., those released by the particles to the solution as they get charged), and the realistic chemistry of the aqueous solution on such electrokinetic phenomena as electrophoresis and electrical conductivity. These assumptions, while having been accepted for dilute conditions (volume fractions of solids well below 1 %, say), are now questioned when dealing with concentrated suspensions. In this work, we present a general electrokinetic cell model for such kind of systems, including the mentioned effects, and we also carry out a comparative study with the standard treatment (the standard solution only contains the ions that one purposely adds, without ionic contributions from particle charging or water chemistry). We also consider an intermediate model that neglects the realistic aqueous chemistry of the solution but accounts for the correct contribution of the added counterions. The results show the limits of applicability of the classical assumptions and allow one to better understand the relative role of the added counterions and ions stemming from the electrolyte in a realistic aqueous solution...

Molecular modeling and Monte Carlo simulation of concentrated aqueous alkali halide solutions at 25 C

Llano-Restrepo, Mario Andres
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 594 p.; application/pdf
ENG
Relevância na Pesquisa
511.434%
A study of concentrated aqueous alkali halide solutions is made at the molecular level, through modeling and computer simulation of their structural and thermodynamic properties. It is found that the HNC approximation is the best integral equation theory to predict such properties within the framework of the primitive model (PM). The intrinsic limitations of the PM in describing ionic association and hydration effects are addressed and discussed in order to emphasize the need for explicitly including the water molecules in the treatment of aqueous electrolyte solutions by means of a civilized model (CM). As a step toward developing a CM as simple as possible, it is shown that a modified version of the SPC model of liquid water in which the Lennard-Jones interaction between intermolecular oxygen sites is replaced by a hard core interaction, is still successful enough to predict the degree of hydrogen bonding of real water. A simple civilized model (SCM) (in which the ions are treated as hard spheres interacting through Coulombic potentials and the water molecules are simulated using the simplified SPC model) is introduced in order to study the changes in the structural features of various aqueous alkali halide solutions upon varying both the concentration and the size of the ions. Both cations and anions are found to be solvated by the water molecules at expense of a breakdown in the hydrogen-bonded water network. Hydration numbers are reported for the first time for NaBr and KBr...

ELECTRICAL FACTORS INFLUENCING THE RATE OF FILTRATION OF AQUEOUS ELECTROLYTE SOLUTIONS THROUGH CELLOPHANE MEMBRANES

White, H. L.; Monaghan, Betty; Urban, Frank
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 20/03/1935 EN
Relevância na Pesquisa
712.8683%
The mechanisms by which electrokinetic factors might influence the filtration rate of aqueous electrolyte solutions through membranes are discussed. The filtration rate of a thorium chloride solution in which the membrane is isoelectric is compared with those of other solutions. The maximum filtration rate is found at the isoelectric concentration, the rate falling as the electrokinetic potential increases. The results demonstrate an inverse relation between the electrokinetic potential and the filtration rate but do not permit the evaluation with any great exactitude of the respective rôles played by the two proposed mechanisms, namely, a stream potential-electroosmotic back-transport and a variation in effective pore diameter due to an orientation of water dipoles determined by electrical factors. Evidence is presented that Lepeschkin's membrane resistance is an artifact.

Equation for the solvent activity correlation in ternary electrolyte solutions

Ricardini, Andres; Passamonti, Francisco Javier; Chialvo, Abel Cesar
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
Relevância na Pesquisa
602.8017%
An analytical equation is proposed for the dependence on composition of the solvent activity of aqueous ternary electrolyte solutions. This equation was derived taking into account the limiting behaviour that must obey the solvent activity in order to be thermodynamically consistent. The correlation of experimental data corresponding to 23 ternary systems was successfully carried out. The results obtained demonstrate an excellent fitting capability of the proposed equation.; Fil: Ricardini, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; Argentina;; Fil: Passamonti, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; Argentina;; Fil: Chialvo, Abel Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica; Argentina;

Effect of Salt Identity on the Phase Diagram for Globular Proteins in Aqueous Electrolyte Solutions

Bostrom, Mathias Anders; Tavares, Frederico W; Ninham, Barry; Prausnitz, John M
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
715.4737%
Monte Carlo simulations are used to establish the potential of mean force between two globular proteins in an aqueous electrolyte solution. This potential includes nonelectrostatic contributions arising from dispersion forces first, between the globular p

Measurement of Interaction Forces between Lignin and Cellulose as a Function of Aqueous Electrolyte Solution Conditions

Notley, Shannon; Norgren, Magnus
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
813.4005%
The interaction between a lignin film and a cellulose sphere has been measured using the colloidal probe force technique as a function of aqueous electrolyte solution conditions. The lignin film was first studied for its roughness and stability using atom

Dependence of the dielectric constant of electrolyte solutions on ionic concentration

Gavish, Nir; Promislow, Keith
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/08/2012
Relevância na Pesquisa
598.95375%
We study the dependence of the static dielectric constant of aqueous electrolyte solutions upon the concentration of salt in the solution and temperature. The model takes into account the orientation of the solvent dipoles due to the electric field created by ions, the ionic response to an applied field, and the effect of thermal fluctuations. The analysis suggests that the formation of ion pairs by a small fraction of disassociated ions can have a significant effect on the static dielectric constant. The model predicts the dielectric has the functional dependence $\varepsilon(c)=\varepsilon_w-\beta L(3\alpha c/\beta)$ where $L$ is the Langevin function, $c$ is the salt concentration, $\varepsilon_w$ is the dielectric of the pure water, $\alpha$ is the total excess polarization of the ions and $\beta$ is the relative difference between the water dipole moment and the effective dipole moment of ion pairs as weighted by the density of ion pairs and their structural rigidity. The functional form gives an extremely accurate prediction of the dielectric constant for a variety of salts and a wide range of concentrations by fitting only the parameter $\beta$.

Glasslike Behavior in Aqueous Electrolyte Solutions

Turton, David A.; Hunger, Johannes; Hefter, Glenn; Buchner, Richard; Wynne, Klaas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/04/2009
Relevância na Pesquisa
609.2551%
When salts are added to water, the viscosity generally increases suggesting the ions increase the strength of the water's hydrogen-bond network. However, infrared pump-probe measurements on electrolyte solutions have found that ions have no influence on the rotational dynamics of water molecules implying no enhance-ment or breakdown of the hydrogen-bond network. Here we report optical Kerr-effect and dielectric relaxa-tion spectroscopic measurements, which have enabled us to separate the effects of rotational and transitional motions of the water molecules. These data show that electrolyte solutions behave like a supercooled liquid approaching a glass transition in which rotational and translational molecular motions are decoupled. It is now possible to understand previously conflicting viscosity data, nuclear magnetic resonance relaxation, and ultrafast infrared spectroscopy in a single unified picture.

Theoretical study of phase behaviour of DLVO model for lysozyme and $\gamma$-crystalline aqueous electrolyte solutions

Melnyk, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/04/2015
Relevância na Pesquisa
709.0203%
Mean spherical approximation (MSA), second-order Barker-Henderson (BH) perturbation theory and thermodynamic perturbation theory (TPT) for associating fluids in combination with BH perturbation theory are applied to the study of the structural properties and phase behaviour of the Derjaguin-Landau-Verwey-Overbeek (DLVO) model of lysozyme and $\gamma$-cristalline aqueous electrolyte solutions. Predictions of the MSA for the structure factors are in good agreement with the corresponding computer simulation predictions. The agreement between theoretical results for the liquid-gas phase diagram and the corresponding results of the experiment and computer simulation is less satisfactory, with predictions of the combined BH-TPT approach being the most accurate.; Comment: 9 pages, 3 figures

Study of Interfacial Tension between an Organic Solvent and Aqueous Electrolyte Solutions Using Electrostatic Dissipative Particle Dynamics Simulations

Mayoral, E.; Nahmad-Achar, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/11/2012
Relevância na Pesquisa
719.445%
The study of the modification of interfacial properties between an organic solvent and aqueous electrolyte solutions is presented by using electrostatic Dissipative Particle Dynamics (DPD) simulations. In this article the parametrization for the DPD repulsive parameters aij for the electrolyte components is calculated considering the dependence of the Flory-Huggins \c{hi} parameter on the concentration and the kind of electrolyte added, by means of the activity coefficients. In turn, experimental data was used to obtain the activity coefficients of the electrolytes as a function of their concentration in order to estimate the \c{hi} parameters and then the aij coefficients. We validate this parametrization through the study of the interfacial tension in a mixture of n-dodecane and water, varying the concentration of different inorganic salts (NaCl, KBr, Na2SO4 and UO2Cl2). The case of HCl in the mixture n-dodecane/water was also analyzed and the results presented. Our simulations reproduce the experimental data in good agreement with previous work, showing that the use of activity coefficients to obtain the repulsive DPD parameters aij as a function of concentration is a good alternative for these kinds of systems.; Comment: 18 pp....

Atomistic simulations of electrolyte solutions and hydrogels with explicit solvent models

Walter, Jonathan; Deublein, Stephan; Reiser, Steffen; Horsch, Martin; Vrabec, Jadran; Hasse, Hans
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/07/2011
Relevância na Pesquisa
502.8017%
Two of the most challenging tasks in molecular simulation consist in capturing the properties of systems with long-range interactions (e.g. electrolyte solutions) as well as systems containing large molecules such as hydrogels. For the development and optimization of molecular force fields and models, a large number of simulation runs have to be evaluated to obtain the sensitivity of the target properties with respect to the model parameters. The present work discusses force field development for electrolytes regarding thermodynamic properties of their aqueous solutions. Furthermore, simulations are conducted for the volume transition of hydrogels in the presence of electrolytes. It is shown that the properties of these complex systems can be captured by molecular simulation.

Hofmeister Effects in Surface Tension of Aqueous Electrolyte Solution

Bostrom, Mathias Anders; Kunz, Werner; Ninham, Barry
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
714.3858%
The surface tension of electrolyte solutions shows marked specific ion effects. We here show an important role for both ionic solvation energies and ionic dispersion potentials in determining this ion specific surface tension of salt solutions. The ion self-free energy changes when an ion moves from bulk solution into the interfacial region, with its decreasing water density profile. We will show that the solvation energies of different ions correlate very well with the surface tension of salt solutions. Inclusion of this distance-dependent self-free energy contribution brings qualitative agreement with experiments and the right Hofmeister series. This is so not only for surface tension changes but also for measured surface potentials. The inclusion of ionic dispersion interaction potentials further improves the agreement with experiments. We discuss how further progress in the theory of the surface tension of salts can be achieved.

Hofmeister Specific Ion Effects in Two Biological Systems

Lo Nostro, Pierandrea; Lo Nostro, Antonella; Ninham, Barry; Pesavento, Giovanna; Fratoni, Laura; Baglioni, Piero
Fonte: Pergamon-Elsevier Ltd Publicador: Pergamon-Elsevier Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
505.40715%
Specific ion effects are studied in two complex biological systems: water absorbance of wool fibers, and growth rates of a halophilic bacterium, Staphylococcus aureus, in different electrolyte solutions.

Osmotic Coefficients and Surface Tensions of Aqueous Electrolyte Solutions: Role of Dispersion Forces

Kunz, Werner; Belloni, Luc; Bernard, Olivier; Ninham, Barry
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
1028.5667%
Osmotic coefficients of a series of 16 aqueous electrolyte solutions are described at concentrations up to about 1 M with the help of HNC calculations and solvent-averaged potentials of charged hard spheres with an additional necessary dispersion potential, omitted from all earlier treatments. The adjusted ionic radii and excess polarizabilities have values of the expected order of magnitude. Whereas the description of the bulk properties is satisfactory, the theory is not so successful in predicting the surface tensions of the corresponding solutions (Hofmeister series). The reasons for this are quite subtle and explored in the text. It is clear now how to make further progress and tackle hydration in a consistent way.