Conductivities Of Dilute Aqueous Solutions Research Articles

Conductivity study with caffeinate anion - Caffeic acid and its sodium and potassium salts

Precise electrical conductivities of dilute aqueous solutions of caffeic acid, sodium caffeinate, potassium caffeinate were determined in the temperature range from 278.15 K to 313.15 K (values for caffeic acid and potassium caffeinate solutions are reported for the first time in this paper). The experimental data of caffeic acid salts were analyzed by using the Kohlrausch and Onsager conductivity equation, yielding the limiting conductances of caffeinate anion, their diffusion coefficients at infinite dilution, and the Stokes radii. The equilibrium constants of the first dissociation step of caffeic acid were evaluated by applying the Quint-Viallard conductivity equations for 1:1 type electrolytes, and the Debye-Hückel expression for activity coefficients. Temperature dependence of the equilibrium constant permitted to obtain the standard thermodynamic functions of the dissociation process. The good agreement between experimental and calculated conductances of caffeic acid indicates the reliability of applied molecular model.

Classical problem of determination of limiting conductances of acetate anion revisited

Precise electrical conductivities of dilute aqueous solutions of acetic acid and its lithium, sodium, potassium and cesium salts were determined from 278.15K to 313.15K. Conductivities of alkali metal acetates from the literature and measured here were discussed in the framework of dissociation and hydrolysis model. This was performed by using the Quint-Viallard conductivity equations for 1:1 type electrolytes and the Debye-Hückel expression for activity coefficients. Excellent agreement between experimental and calculated conductances permitted to evaluate over the investigated temperature range, a consistent and reliable set of the limiting conductances of acetate anion, their diffusion coefficients at infinite dilution and the Stokes radius. Without using additional parameters, the classical problem of representation of acetic acid conductivities in dilute solutions was reexamined and solved, indicating internal consistency of applied molecular models.

The Representation of Electrical Conductances for Polyvalent Electrolytes by the Quint–Viallard Conductivity Equation

Electrical conductivities of dilute aqueous solutions of aluminum sulfate were determined and analyzed in terms of a strongly associated electrolyte of the 3:2 type. The conductivities reported here were determined from 15 to 35 °C. Representation of conductances, in the framework of the ion association model, was performed using the Quint–Viallard conductivity equations for highly charged electrolytes and the Debye–Huckel expression for activity coefficients. Determined apparent association constants K a(T) were considered as adjustable parameters. The determined limiting conductances of the trivalent aluminum ion λ0((1/3)Al3+) are considerably higher than those reported in the literature. Available specific conductivities in concentrated aqueous solutions of aluminum sulfate were fitted by a new empirical equation with only three adjustable parameters.

Representation of Electrical Conductances by the Quint–Viallard Conductivity Equation. Part 6. Unsymmetrical 2:1 Type “Complex Ions” Electrolytes: Cadmium Bromide and Cadmium Iodide

Systematic and precise measurements of electrical conductivities of dilute aqueous solutions of cadmium bromide and cadmium iodide were performed from 15 to 35 °C. The conductances were interpreted in terms of a molecular model that includes a mixture of two 1:1 and 2:1 electrolytes. The molar limiting conductances of $$ \lambda $$ 0(CdX+, T) ions, the equilibrium constants of formation of CdX+ complexes K(T) and the corresponding standard thermodynamic functions were evaluated using the Quint–Viallard conductance equations, the Debye–Huckel equations for activity coefficients and the mass action equations. Mathematical representations are also presented to an extension of molecular models, to the simultaneous formation of MeX+ and MeX2 species and to the possibility of hydrolysis reactions with formation of Me(OH)+ ions.

A Conductance Study of Guanidinium Chloride, Thiocyanate, Sulfate, and Carbonate in Dilute Aqueous Solutions: Ion-Association and Carbonate Hydrolysis Effects

We study the conductance of dilute aqueous solutions for a series of guandinium salts at 298.15 K. The experimental molar conductivities were analyzed within the framework of the Quint-Viallard theory in combination with Debye-Hückel activity coefficients. From this analysis, we find no evidence for significant ion association in aqueous solutions of guanidinium chloride (GdmCl) and guanidinium thiocyanate (GdmSCN), and the molar conductivity of these electrolytes can be modeled assuming a complete dissociation. The limiting ionic conductivity of the guanidinium ion (Gdm(+)) is accurately determined to λ(Gdm(+)) = 51.45 ± 0.10 S cm(2) mol(-1). For the bivalent salts guanidinium sulfate (Gdm(2)SO(4)) and guanidinium carbonate (Gdm(2)CO(3)), the molar conductivities show small deviations from ideal (fully dissociated electrolyte) behavior, which are related to weak ion association in solution. Furthermore, for solutions of Gdm(2)CO(3), the hydrolysis of the carbonate anion leads to distinctively increased molar conductivities at high dilutions. The observed ion association is rather weak for all studied electrolytes and cannot explain the different protein denaturing activities of the studied guanidinium salts, as has been proposed previously.

Representation of Electrical Conductances for Polyvalent Electrolytes by the Quint-Viallard Conductivity Equation. Part 2. Symmetrical 3:3 Type Electrolytes. Dilute Aqueous Solutions of Rare Earth Hexacyanoferrates(III) and Hexacyanocobaltates(III)

Literature values of the electrical conductivities of dilute aqueous solutions of trivalent rare earth hexacyanoferrates(III) (La, Pr, Nd, Sm, Gd) and of rare earth hexacyanocobaltates(III) (La, Nd, Sm, Y) were reexamined within the framework of the Quint-Viallard conductivity equation in order to obtain a uniform representation of their conductivities. It was observed that the limiting conductances of electrolytes at infinite dilution depend weakly on the applied conductivity equation, whereas the derived ion association equilibrium constants vary considerably and therefore should be treated rather as fitting parameters.

The Representation of Electrical Conductances for Polyvalent Electrolytes by the Quint-Viallard Conductivity Equation. Part 3. Unsymmetrical 3:1, 1:3, 3:2, 4:1, 1:4, 4:2, 2:4, 1:5 1:6 and 6:1 Type Electrolytes. Dilute Aqueous Solutions of Rare Earth Salts, Various Cyanides and other Salts

Electrical conductivities of dilute aqueous solutions for unsymmetrical electrolytes of the type 3:1, 1:3, 3:2, 4:1, 1:4, 4:2, 2:4, 1:5 1:6 and 6:1 are reexamined in the framework of the Quint-Viallard conductivity equations, in order to obtain a uniform representation of their conductivities. The molar and equivalent limiting conductances were evaluated with ion association constants, which were treated as adjustable parameters. The derived values were compared with corresponding results from the literature. The following electrolytes are considered: rare earth (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) halides, perchlorides, nitrates and sulfates; hexamminecobalt and tris-ethylenediaminecobalt halides, perchlorides, nitrates and sulfates; [Ni2(trien)3]Cl4, [Pt(pn)3]Cl4, [Co2(trien)3]Cl6; cyanides K3[Fe(CN)6], K3[Co(CN)6], M3[W(CN)8] with M=Na, K, Rb, Cs; Ca2[Fe(CN)6], K4[Fe(CN)6], K4[Mo(CN)8], K4[W(CN)8], K4[Ru(CN)8], (Me4N)4[Fe(CN)6], (Pr4N)4[Fe(CN)6], K4[Mo(CN)8], (Me4N)4[Mo(CN)8], (Et4N)4[Mo(CN)8] and (Pr4N)4[Mo(CN)8]; phosphates Na4P2O7, Na4P4O12, Na5P3O10, Na6P6O18 and (Me4N)4P4O12.

Representation of Electrical Conductances for Polyvalent Electrolytes by the Quint-Viallard Conductivity Equation. Part 1. Symmetrical 2:2 Type Electrolytes. Dilute Aqueous Solutions of Alkaline Earth Metal Sulfates and Transition Metal Sulfates

Literature values of the electrical conductivities of dilute aqueous solutions of alkaline metal sulfates (BeSO4, MgSO4, CaSO4, SrSO4) and of transition metal sulfates (MnSO4, FeSO4, CoSO4, NiSO4, CuSO4, ZnSO4, CdSO4) were reexamined within the framework of the Quint-Viallard conductivity equations in order to obtain a uniform representation of conductivities. It was observed that the limiting conductances of electrolytes at infinite dilution are very similar irrespective of the applied conductivity equation, whereas the derived ion association equilibrium constants vary considerably. The ion association equilibrium constants are therefore of doubtful physical value and should be treated rather as just fitting parameters.

Anomalous electrical conductivity of aqueous solutions in submicron cracks and gaps

By a modified technique of contact electrical resistance (CER), the electrical conductivity of alcohol and aqueous solutions of acids, salts, and bases in submicron gaps between clean contact surfaces have been measured. Alcohol solutions of water content below 10 do not have substantial electrical conductivity, while at contents of about 50 their electrical conductivity becomes similar to that of aqueous solutions. The electrical conductivity of dilute aqueous solutions is anomalously high. It is higher than that of strong solutions of salts and acids, in contradiction with the ionic theory of electrical conductivity. A conclusion on the nonionic nature of the electrical conductivity of aqueous solutions in submicron gaps is formulated. A model of electrical conductivity assuming the formation of a labile spatial hydrogen-bond network in the contact gap is proposed and used to explain the results.

Conductance of Dilute Sodium Acetate Solutions to 469 K and of Acetic Acid and Sodium Acetate/Acetic Acid Mixtures to 548 K and 20 MPa

In order to obtain accurate association constants for sodium acetate, a very precise flow method was used to measure the electrical conductivity of dilute aqueous solutions of sodium acetate at ambient conditions and 469 K and 20 MPa. Measurements at ambient conditions, 469 and 548 K and 20 MPa, were also made on sodium acetate/acetic acid mixtures and acetic acid. In order to determine the limiting the equivalent conductances and the association constant for sodium acetate, and dissociation constant for acetic acid, the results were fitted to two modern conductance equations (Fuoss–Hsia–Fernandez–Prini and Turq–Blum–Bernard–Kunz) with accompanying activity coefficient models (mean spherical approximation and the Debye–Huckel with the Bjerrum distance). The choice of conductance equation, activity coefficient model, assumed values for the limiting equivalent conductance for minor species, and assumed equilibrium constants for minor reactions, did not significantly change the resulting equilibrium constants. The insensitivity of the calculated equilibrium constants to these choices in conjunction with the inherent precision of the flow conductance technique leads us to believe that the present results are the most accurate sodium acetate ion-pairing constants published to date. Our results for acetic acid are in good agreement with previously published results from other laboratories.

Protonation constant of caffeine in aqueous solution

The decreases in the conductivities of dilute aqueous solutions of hydrochloric acid and of sodium chloride on the addition of various concentrations of caffeine have been measured from 25 to 50 °C. The viscosities of the caffeine solutions have also been determined. The results, interpreted by the isodesmic model for caffeine self-association, showed that only the monomeric caffeine molecules in solution were protonated. The dissociation constant Hcaf+ was found to be 0.82, 0.76 and 0.69 mol kg–1 at 25, 38, and 50 °C, respectively. The dimerisation model for caffeine association failed to fit the conductivity results.

The conductivity of dilute aqueous solutions of magnesium chloride at 25�C

There is a disagreement in the literature regarding the best value of Λo[1/2MgCl2]. For this reason, the conductivity of dilute aqueous MgCl2 solutions have been determined at 25°C. The new experimental data and those available in the literature have been analyzed with two theoretical treatments of electrolytic conductivity. On the basis of that analysis, the values 129.72±0.05 and 53.40±0.05 S-cm2-mol−1 for Λo[1/2MgCl2] and λo[1/2Mg2+], respectively, are recommended.

The conductivity of dilute solutions of mixed electrolytes. Part 1.—The system NaCl–BaCl2–H2O at 298.2 K

The conductivity of dilute aqueous solutions of NaCl–BaCl2 have been determined at various ionic compositions. In order to assess the capacity of modern theories of conductivity to deal with mixed electrolyte solutions, we have tested the theories of Quint and Viallard (QV) and of Lee and Wheaton (LW). While both theories permit a consistent description of the conductivity of the mixtures, the QV expression is simpler and yields distance parameters which depend linearly on the cationic composition weighted by the square of the charge of the cation, i.e. the conductivity of the mixtures may be described with QV in terms of the behaviour of the component binary electrolyte solutions. On the other hand, it is found that the LW treatment is able to deal with more concentrated solutions than that of QV, but the conductivity of the mixture cannot be expressed in terms of those of the pure binary electrolytes.

Determination of Lower and Middle Linear Saturated Fatty Acids in Water

The conductivities of dilute aqueous solutions of lower and middle linear saturated fatty acids were determined at 25 C. The characteristic relationships between conductivity and concentration of solutions of the fatty acids were obtained for each carbon number of the acid, respectively. The experimental equation to present conductivity of a solution as a function of total ionic molar concentration of fatty acids is given by K= 0.375 x C+ 2.0 x 10-6 where K is conductivity (mho/cm), and C is total ionic molar concentration (M) of fatty acid. These relationships and the equation would serve to calibrate the amount of fatty acids in water from conductivity measurement when fatty acids are the predominant components in water and the measurement of conductivity is not interfered with the other ions.

Conductance of dilute aqueous solutions of hexafluorophosphoric acid at 25.deg.

Conductance of dilute aqueous solutions of hexafluorophosphoric acid at 25.deg.

The Experimental Requirements for Making Accurate High Pressure Conductance Measurements on Aqueous Solutions with Pt‐in‐Glass Cells

Experimental procedures are described for obtaining accurate high pressure coefficients of conductance of dilute aqueous solutions of strong electrolytes (≥2 mM) in the ranges 1–2250 atm and 3°–55°C. Procedures are developed such that an over‐all accuracy of 0.1% in the high pressure conductance is obtained. It is shown that in order to obtain reproducible and accurate results great attention must be paid to the stability of the electrode seal through the body of the conductance cell. Pt foil of suitably small cross section has been sealed to the Pyrex cell wall using soft glass and ten intermediate grades. It is shown that this produces an electrode seal which is leak‐free and stable over the entire range of temperature and pressure studied. Also incorporated into the seal is a multiple‐wire cage design which imparts high mechanical stability to the external electrode terminals. A capillary cell is described which is compensated for anisotropic distortion under pressure and which is suitable for precise measurements with solutions more concentrated than 5 mM. It is shown that the cell constant variation with pressure, and the effects of anisotropic distortions of the electrodes under pressure, can be determined to within 0.02% for this and other compensated electrode configurations. The errors arising from contamination of the solutions with impurities are described. It is shown that a typical weak electrolyte impurity must be kept below ∼1% of the (∼2 mM) salt concentration if an over‐all accuracy of 0.1% is to be attained at 2000 atm. Similarly, the concentration of dissolved O2 must be maintained below ∼50 µM for a 2 mM salt solution.

Activation energy of conduction of aqueous solutions in capillaries

Evidence is presented which may support the suggestion made by Derjaguin and others that a long-range ordering of the structure of water and other liquids may exist near interfaces. Data are presented on the conductance of dilute aqueous solutions of HCl in capillaries of diameter as small as a few microns, and on the variation of this conductance with change in temperature. Activation energies of conduction calculated from these data show a value for solutions held in small capillaries which is different from that obtained for the same solutions in the bulk by a factor of as much as 100%.

Light scattering and ultra-violet absorption studies on dilute aqueous solutions of poly-4-vinylpyridinium chloride

The discontinuous concentration of viscosity, streaming birefringence and conductance of dilute aqueous solutions of poly-4-vinylpyridinium chloride is attributed, on the basis of light scattering and spectra measurements, to the extensive hydrolysis of the poly-ions in dilute solution. The decrease in the charge on the poly-ion consequent on the hydrolysis produces changes in the shape and size which may explain the observed hydrodynamic properties.

The conductivities of dilute aqueous solutions of potassium ferrocyanide and calcium ferrocyanide

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