Conductance of Unassociated Electrolytes.

Fuoss, Raymond M.; Onsager, Lars

doi:10.1021/j150551a038

Cited by 249 publications

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“…A mass action equilibrium between free and paired ions was postulated, with associated constant KA = (1 -Y)ICTf2 [8] where activity coefficient f was set equal to the Debye-Huckel limiting value, -In f = flx/2, in which iB = e2/DkT and x2 = 8irnf3. For the primitive model (7) KA = (47rN/1000) 0" r2exp(/3/r)dr [9] The 2-parameter equation 7, A = A(c; AO, KA) satisfactorily reproduces observed data for systems whose conductance curves lie below the limiting tangent (ay < 1), but it is useless for the analysis of data for most electrolytes in solvents of high dielectric constant, for which A(c) > ALT, because -y(Ao -SC1/211/2) can never exceed (Ao -Sc'12), because y < 1.Theoretical investigations (8)(9)(10)(11)(12)(13)(14)(15), based on the primitive model, of the effects of the higher terms [of order (eij)m], which had been neglected in the integration of the equation of con-16 …”

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confidence: 68%

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Paired ions: Dipolar pairs as subset of diffusion pairs

Fuoss

1978

Proc. Natl. Acad. Sci. U.S.A.

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118

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Previous models for which theories of electrolytic conductance have been developed are reviewed. Discrepancies between theoretically derived values of parameters and parameters characteristic of real physical systems suggested the following revised model. Ions are counted as diffusion pairs if their center-to-center distance r is in the range a < r < R, in which a is contact distance and R is the diameter of the Gurney cosphere. A fraction a of these pairs diffuse to contact to form nonconducting dipolar pairs; a/(1 -a) = e(-Es/k) in which E, is the difference in energy between a iffusion pair at r = R and a contact pair, k is the Boltzmann constant, and T is the absolute temperature. This model permits separate treatment of long-range and short-range interionic effects. The former (relaxation field and electrophoresis) depend on R and the values of the dielectric constant and viscosity of the pure solvent. The latter (formation of dipolar pairs) is described by Es, or (4) divC(fq; vii) + div2 (fji Vji) = 0 [2] in which fji = ninji gives the probability of finding simultaneously an ion of species j in an element of volume dVI and an i ion in dV2; v j is the velocity of the i ion in dV2 (and congruently for fqj and vi1). Local concentrations nfj = nj exp(-eiij/kT) = njet in which 4'j is the potential at the distance r from the j ion. In the presence of an external field, the ALT = Ao(I -acl/2) -floc/2 [6] in which ao and 13o depend only on the valence type of the ions, on the dielectric constant D and viscosity X of the continuum, and on absolute temperature T.Eq. 6 assumes that all the ions participate in net transport of charge; if a fraction (1 -y) is assumed to form nonconducting pairs (5), Eq. 1 becomes the Fuoss-Kraus (6) [7] in which S = (aoAo + Qo). A mass action equilibrium between free and paired ions was postulated, with associated constant KA = (1 -Y)ICTf2 [8] where activity coefficient f was set equal to the Debye-Huckel limiting value, -In f = flx/2, in which iB = e2/DkT and x2 = 8irnf3. For the primitive model (7) KA = (47rN/1000) 0" r2exp(/3/r)dr [9] The 2-parameter equation 7, A = A(c; AO, KA) satisfactorily reproduces observed data for systems whose conductance curves lie below the limiting tangent (ay < 1), but it is useless for the analysis of data for most electrolytes in solvents of high dielectric constant, for which A(c) > ALT, because -y(Ao -SC1/211/2) can never exceed (Ao -Sc'12), because y < 1.Theoretical investigations (8)(9)(10)(11)(12)(13)(14)(15), based on the primitive model, of the effects of the higher terms [of order (eij)m], which had been neglected in the integration of the equation of con-16

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mentioning

confidence: 68%

“…Theoretical investigations (8)(9)(10)(11)(12)(13)(14)(15), based on the primitive model, of the effects of the higher terms [of order (eij)m], which had been neglected in the integration of the equation of con-16 …”

Section: Introductionmentioning

confidence: 99%

Paired ions: Dipolar pairs as subset of diffusion pairs

Fuoss

1978

Proc. Natl. Acad. Sci. U.S.A.

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118

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“…From the measured conductivities, one may roughly estimate the ion concentration n of F − ions with the help of the Fuoss-Onsager theory of molar conductivities (Fuoss & Onsager 1957;Miyoshi 1973). The estimated values are summarized in table 2.…”

Section: Resultsmentioning

confidence: 99%

Electric field assisted hydrogen fluoride etching of silica

Neto

Lesche

2009

Proc. R. Soc. A.

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The influence of electric fields on the velocity of the chemical reaction 4HF + SiO 2 → SiF 4 + 2H 2 O in aqueous solution is investigated experimentally. The field strengths used were high enough to measure nonlinear effects. The results permit a critical analysis of a theoretical model known in literature. The basic idea of dipole orientation changing the rate of the primary step of the chemical reaction can explain the experimental data, but several important details of the original model had to be changed. The primary step involves two hydrogen fluoride (HF) molecules rather than one, and field screening by mobile ions has a significant influence causing nonlinear effects. The fact that field screening plays an important role implies that electric field-assisted HF etching of silica may by used as an instrument for measuring ion concentrations in highly concentrated electrolytes. The data measured may be well described by a theoretical model based on mean field approximations. The results give an insight into the structure of highly concentrated hydrofluoric acid and also permit a critical analysis of applications of the effect in measuring electric fields written in glass samples by electrothermal poling. The effect may also be used for shaping glass surfaces.

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“…I t should be pointed out, however, that & , is determined by the value of J in the difference term (J -K,f2A) in eq. [2], and when K, is large, or the data are of relatively low precision, the resulting value of &, is not expected to be reliable (22). T o determine a self-consistent set of association constants from the available data it was decided to fix the ion size parameter &, , thereby making use of the fact that the difference term itself, (J -KJ2h), can be determined with some precision.…”

Section: Ion Size Parameters From the Conductance Equationmentioning

confidence: 99%

Application of the Fuoss–Onsager theory to conductance data for sodium and potassium iodide solutions in various solvents

Janz¹,

Tait²

1967

Can. J. Chem.

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The 1957 Fuoss-Onsager conductance equation has been used to analyze data for sodium iodide and potassium iodide solutions in 13 one-component solvents, ranging from water (dielectric constant 78) to pyridine (dielectric constant 12). Values of the unknowns Ao, d J , an ion size parameter, and, where appropriate, K,, the ion association constant, are calculated.In solvents of high dielectric constant it is found that the salts are completely dissociated ( K , = 0) and the mean value of &J is 4.5 A for each salt. However, the ion size parameters from the conductance equation do not seem to have any physical significance in solvents of lower dielectric constant, where there is evidence of ionic association. An analysis of these data is considered in which the Fuoss-Onsager equation reduces to a one-parameter equation, with K, as the unknown. The conductance data for sodium and potassium iodide can then be understood if the closest distance of approach of the ions is 4.5 A in all 13 solvents.

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Conductance of Unassociated Electrolytes.

Cited by 249 publications

References 0 publications

Paired ions: Dipolar pairs as subset of diffusion pairs

Paired ions: Dipolar pairs as subset of diffusion pairs

Electric field assisted hydrogen fluoride etching of silica

Application of the Fuoss–Onsager theory to conductance data for sodium and potassium iodide solutions in various solvents

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