Comment on “The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion–ion correlations” [J. Chem. Phys. 133, 154507 (2010)]

Fraenkel, Dan

doi:10.1063/1.3575598

Cited by 8 publications

(8 citation statements)

References 5 publications

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“…A recent approach by Fraenkel also uses the DH theory as a starting point [15][16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

Valiskó¹,

Boda²

2014

The Journal of Chemical Physics

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Our implicit-solvent model for the estimation of the excess chemical potential (or, equivalently, the activity coefficient) of electrolytes is based on using a dielectric constant that depends on the thermodynamic state, namely, the temperature and concentration of the electrolyte, ε(c, T). As a consequence, the excess chemical potential is split into two terms corresponding to ion-ion (II) and ion-water (IW) interactions. The II term is obtained from computer simulation using the Primitive Model of electrolytes, while the IW term is estimated from the Born treatment. In our previous work [J. Vincze, M. Valiskó, and D. Boda, "The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations," J. Chem. Phys. 133, 154507 (2010)], we showed that the nonmonotonic concentration dependence of the activity coefficient can be reproduced qualitatively with this II+IW model without using any adjustable parameter. The Pauling radii were used in the calculation of the II term, while experimental solvation free energies were used in the calculation of the IW term. In this work, we analyze the effect of the parameters (dielectric constant, ionic radii, solvation free energy) on the concentration and temperature dependence of the mean activity coefficient of NaCl. We conclude that the II+IW model can explain the experimental behavior using a concentration-dependent dielectric constant and that we do not need the artificial concept of "solvated ionic radius" assumed by earlier studies.

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“…A recent approach by Fraenkel also uses the DH theory as a starting point [15][16][17][18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

Valiskó¹,

Boda²

2014

The Journal of Chemical Physics

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“…A positive ISP nonadditivity ( d > 0) in halide electrolytes is attributable to polarization effects ,, exerted by a small cation on a larger halide ion upon mutual approach and collision. It is well-known that such polarization elongates the contact distance between the positive and negative centers of the counterions; this is attributed to an increased covalency of the ion–ion bonding interaction.…”

Section: Resultsmentioning

confidence: 99%

“…Optimization of the fit with experiment sometimes requires adjustment of the cationic diameter, especially for small and highly charged cations (see Table ). Also, the counterion’s distance of closest approach ( a ) may not be the sum of the respective radii, thus reflecting specific effects, e.g., a deformation of the spherical shape of a large anion due to its polarization by a small cation. , …”

Section: Discussionmentioning

confidence: 99%

Computing Excess Functions of Ionic Solutions: The Smaller-Ion Shell Model versus the Primitive Model. 2. Ion-Size Parameters

Fraenkel

2014

J. Chem. Theory Comput.

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A recent Monte Carlo (MC) simulation study of the primitive model (PM) of ionic solutions ( Abbas, Z. et al. J. Phys. Chem. B 2009 , 113 , 5905 ) has resulted in an extensive "mapping" of real aqueous solutions of 1-1, 2-1, and 3-1 binary electrolytes and a list of "recommended ionic radii" for many ions. For the smaller cations, the model-experiment fitting process gave much larger radii than the respective crystallographic radii, and those cations were therefore claimed to be hydrated. In Part 1 (DOI 10.1021/ct5006938 ) of the present work, the above study for the unrestricted PM - dubbed MC-UPM - has been confronted with the Smaller-ion Shell (SiS) treatment ( Fraenkel, D. Mol. Phys. 2010 , 108 , 1435 ), or "DH-SiS", by comparing the range and quality of model-experiment fits of the mean ionic activity coefficient as a function of ionic concentration. Here I compare the ion-size parameters (ISPs) of "best fit" of the two models and argue that since ISPs derived from DH-SiS are identical with (or close to) crystallographic or thermochemical ionic diameters for both cations and anions, and they do not depend on the counterion - they are more reliable, as physicochemical entities, than the PM-derived "recommended ionic radii".

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“…(This is apparent because the SiS fit, with the same ISPs, is excellent even at very low concentration at which thermodynamic rigor is unnecessary.) Since, in many cases, ion-size values of binary electrolytes average to ∼3 Å or less, the core potential contribution may be negligible, or very small, up to a quite large concentration; , for example, for 1–1 electrolytes, core effects may be ignored up to ∼1 m , or even higher molality. In the case of aqueous HCl, relevant to the present paper, with average ionic size of ∼2.4 Å, the core effect may be very small at even 3 or 4 m .…”

Section: Introductionmentioning

confidence: 99%

Effect of Solvent Permittivity on the Thermodynamic Behavior of HCl Solutions: Analysis Using the Smaller-Ion Shell Model of Strong Electrolytes

Fraenkel

2011

J. Phys. Chem. B

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The recently introduced smaller-ion shell (SiS) treatment of strong binary electrolyte solutions [Fraenkel, D. Mol. Phys. 2010, 108, 1435] that extends the Debye-Hückel theory to size-dissimilar ions is very effective for many electrolytes of various families up to moderate ionic concentration. The (molal) mean ionic activity coefficient, γ(±), as a function of the reciprocal screening length, κ, hence ionic strength, I, is given by an analytic mathematical expression that incorporates the three ion-size parameters (ISPs). Experimental γ(±) data are fitted with calculated values derived from ISPs that seem to adequately represent the relevant mean effective ionic sizes. The SiS analysis has been lately shown effective for aqueous HCl, HBr, HI, and HClO(4) at 25 °C, at which the solvent permittivity, ε, is 78.4 [Fraenkel, D. J. Phys. Chem. B 2011, 115, 557]. In this paper, the behavior of HCl in solvents ranging in ε between approximately 10 and 80 is analyzed and discussed. The SiS treatment is found again suitable for computing γ(±) values that agree with experiment. Within the concentration range of the available experimental data, ion pairing is not indicated and, contrary to literature claims, HCl appears fully ionized even at 0.5 m (molal) with ε < 10. ISPs do not seem to be affected by temperature, but co-ion ISPs increase linearly with 1/ε. The chemical nature of the solution has no observable effect on γ(±) and on ISPs. The present analysis supports the view that electrolyte theories in which the solvent is considered at the McMillan-Mayer level can be successful and valuable.

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Comment on “The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion–ion correlations” [J. Chem. Phys. 133, 154507 (2010)]

Abstract: The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations The Journal of Chemical Physics 133, 154507 (2010)

Cited by 8 publications

References 5 publications

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

The effect of concentration- and temperature-dependent dielectric constant on the activity coefficient of NaCl electrolyte solutions

Computing Excess Functions of Ionic Solutions: The Smaller-Ion Shell Model versus the Primitive Model. 2. Ion-Size Parameters

Effect of Solvent Permittivity on the Thermodynamic Behavior of HCl Solutions: Analysis Using the Smaller-Ion Shell Model of Strong Electrolytes

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