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Abstract  

Using several reaction examples with experimentally determined rate equations, traditional mass-action rate equations are shown to be simplified forms of polynomial approximation to a general rate function derived by non-equilibrium thermodynamics for a mixture of fluids with linear transport properties. The mass-action kinetic law is thus proved also on the macroscopic level and limited to this type of fluids.

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Abstract  

A model for treating the sorption of metal ions on hydrous metal oxides was established based on the assumptions that these materials are weakly acidic cation exchangers and have a discrete exchanger phase. The experimental results of the sorption of metal ions on the hydrous niobium(V) and tin(IV) oxides are found to be consistent with the formulas derived from the model by considering that the charge balance and the mass action law hold in the exchanger phase and cations are sorbed by the distribution between this phase and the bulk aqueous phase.

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Abstract  

The extraction of hydrochloric acid by trilaurylamine (TLA) dissolved in benzene was studied in the presence and in absence of n-octanol. The extraction of HCl was found to be enhanced by the addition of octanoi to the organic phase. In order to explain this effect by means of the law of mass action, the systems TLA-HCL-benzene and n-octanol-HCl-benzene as well as TLA-octanol-benzene were also studied. It was found that TLA reacts with octanol to form a complex, TLAROH, while the octanol itself associates in benzene to form dimers and tetramers, although it does not extract HCl alone from the dilute solutions used in the present study. The enhancement of the extraction of HCl by TLA upon the addition of n-octanol could be described by the formation of the species TLA·ROH·HCl and its stability constant was determined.

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Abstract  

Aqueous solutions containing poly(vinyl-pyrrolidone) and sodium caprylate, or poly(vinyl-pyrrolidone) and tetraethylammonium perfluorooctanesulfonate,respectively, have been investigated by volumetric, ionic conductivity and surface tension methods. The presence of an interaction region has been determined from conductivity and surface tension. The width of such a region depends on the amount of polymer in the mixture,temperature, surfactant content and added electrolyte (NaCl). The observed behaviour was explained in terms of the combined effects played by the alkyl-chain hydophobicity, polar head group(s) and counter-ions. An approximate solution to a mass action model for the binding of surfactants onto polymers has been introduced. It allows determining the width of the interaction region as a function of polymer mass percent in the mixture.

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Abstract  

A new method has been developed to measure a strong ligand in oceanic dissolved organic matter (DOM) by Th complexation in acidic media and the adsorption of the Th complex onto XAD-2 resin. Th reacts quantitatively with organic binding site of DOM in strong acid media (around 0.1M H+ solution), which is equilibrated within 24 hours. According to mass action analysis, Th forms a 11 complex with the binding site in DOM, whose conditional stability constant is 106.7M–1. The conditional stability constant of the Th complex in DOM is in good agreement with that determined for oceanic Particulate Matter (PM) under similar experimental conditions. This finding suggests that the chemical properties of the strong ligand in DOM are similar to these in biogenic PM. The Th-complexing capacity in DOM, which corresponds to the total concentration of the strong organic ligand, can be determined (2–3 nM in surface waters) in a small volume (about 200 ml). The method has a detection limit of approximately 0.05 nM for the thorium-complexing capacity of DOM by using230Th.

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Abstract  

A sequential leaching experiment for chemical speciation of particulate uranium in seawater was carried out using solution chemistry techniques. Mass action analysis on the leaching processes reveals that the major species of particulate uranium in seawater is an organic complex of uranium(VI), which is dissociated completely in the leaching solution of pH 1.0. Inert uranium, which is not dissolved in the leaching solution of pH 1.0, exists is suspended matter although it is a minor constituent. The result suggests that this species in an organic complex of uranium(IV). The analysis of the experimenmt deduces that an organic binding site in suspended matter reacts as a polydentate ligand, which has more than two stepwise protonation constants within the pH range of 2.0 to 8.2. The conditiona stability constant of the organic uranium complex in suspended matter under the conditions of seawater is within the following range: 12<log Kc,U<16. These findings suggest stronglt that the organic binding site in suspended matter can form stable chelates with metallic elements.

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The single components of association colloids are amphiphilic molecules, which are held together by van der Waals forces and/or hydrogen interactions. The thermodynamic parameters associated with the aggregation behaviour of amphiphiles depend on the chemical nature of the molecules as well as their environmental conditions (temperature, ionic strength, etc.). The systems studied and presented in this paper are association colloids, also known as micellar systems, which are formed of biological relevant detergents (e.g. bile salts, fatty acids). Information concerning the self-organisation (self-aggregation) of such micellar colloids can be easily obtained from isothermal titration calorimetry (ITC), as the critical micelle/aggregation concentration, the number of molecules (n) associated in the aggregate and the heat of aggregation. A complete thermodynamic description (ΔH, ΔS, ΔG, ΔC p) of the micellar colloids can be derived from the ITC data, allowing insights into the formation and stability of these colloidal systems. Based on the mass action model, taking into account counter ion binding, the ITC titration curves were simulated, and the aggregation number n of the aggregates derived. Isothermal titration calorimetry has a considerable advantage compared to other methods, because the critical micellisation concentration, the thermodynamic parameters of the aggregation process, and the aggregation numbers can be determined directly from one experiment.

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Abstract  

Liquid-liquid extraction of uranium(VI) (UO2 2+) from aqueous acidic (HCl and HNO3) solutions into a co-existing organic phase containing Alamine 308 (triisooctyl amine), TBP (tri-n-butyl phosphate) or CYANEX 302 (bis(2,4,4-trimethylpentyl) monothiophosphinic acid) and diluent (toluene) was studied at isothermal conditions (298.2 K) at aqueous phase acidity varying in the range 0.5-6 mol/dm3. All solvent systems exhibit a maximum distribution ratio restricted in the acidity range 3-4 mol/dm3. An obvious difference in extraction behavior through amine system has been observed for two acids, HCl and HNO3, distinguishing the divergent interactions attributed to the different mechanism of complexation depending on the acidic medium. The high degree of separation of UO2 2+ from HNO3 solution is feasible through a complex formation with extractants ranging in the order CYANEX 302 > TBP > Alamine 308. The results were correlated using various versions of the mass action law, i.e., a chemodel approach and a modified version of the Langmuir equilibrium model comprising the formation of one or at least two U(VI)-extractant aggregated structures.

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Abstract  

The power–time curves of micellar formation of two anionic surfactants, sodium laurate (SLA) and sodium dodecyl sulfate (SDS), in N,N-dimethyl acetamide (DMA) in the presence of various long-chain alcohols (1-heptanol, 1-octanol, 1-nonanol and 1-decanol) were measured by titration microcalorimetry at 298 K. The critical micelle concentrations (CMCs) of SLA and SDS under various conditions at 298 K were obtained based on the power–time curves. Thermodynamic parameters (
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\Updelta H^\circ_{\text{mic}}$$ \end{document}
,
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\Updelta S^\circ_{\text{mic}}$$ \end{document}
and
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\Updelta G^\circ_{\text{mic}}$$ \end{document}
) for micellar systems at 298 K were evaluated according to the power–time curves and the mass action model. The influences of the number of carbon-atom and the concentration of alcohol were investigated. Moreover, combined the thermodynamic parameters at 303, 308 and 313 K in our previous work and those of 298 K in the present work for SLA and SDS in DMA in the presence of long-chain alcohols, an enthalpy–entropy compensation effect was observed. The values of the enthalpy of micellization calculated by direct and indirect methods were made a comparison.
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Abstract  

The micellization characteristics of sodium n-dodecyl sulfate (SDS) have been investigated by microcalorimetric technique at conditions close to the physiological ones. The thermodynamics of micellization were studied at 20, 25, 30, 35 and 40 °C in 50 mM HEPES buffer, pH 7.4 and 160 mM NaCl using isothermal titration calorimetric (ITC) technique. The calorimeter can operate in a stepwise addition mode, providing an excellent method of determination of critical micelle concentration (CMC) and enthalpy of demicellization (and hence micellization). It can as well distinguish between aggregating and non-aggregating amphiphiles (solutes) in solution. The dilution enthalpy (∆H dil) was calculated and graphed versus concentration in order to determine the micellization enthalpy (∆H mic) and CMC. In addition to the CMC and ∆H mic, the effective micellar charge fraction (α) of the ionic surfactant micellization process can also be determined from ITC curves. The Gibbs free energy of the micellization (∆G mic), entropy of the micellization (∆S mic), and specific heat capacity of the micellization (∆C P,mic) process have been evaluated by the direct calorimetric method (mass-action model) as well as by the indirect method of van’t Hoff by processing the CMC and α results of microcalorimetry at different temperatures. The differences of the results obtained by these two procedures have been discussed. The presence of NaCl (160 mM) in the solutions decreased the CMC of SDS. The enthalpy changes associated with micelle dissociation were temperature-dependent, indicating the importance of hydrophobic interactions. The ∆G mic was found to be negative, implying, as expected, that micellization occurs spontaneously once the CMC has been reached. The values of ∆G mic were found to become more negative with increasing temperature and the ∆S mic was found to decrease with increasing temperature in both models.

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