Reference Electrolyte Assumption Research Articles

Molar Volumes and Heat Capacities of Electrolytes and Ions in N,N-Dimethylformamide

Densities and heat capacities of various 1:1 and higher-charged electrolytes have been measured in N,N-dimethylformamide (DMF) at 25 degrees C using a series-connected flow densimeter and Picker calorimeter. Standard molar volumes V (o) and isobaric heat capacities C p (o) derived from these data were split into their ionic contributions using the tetraphenylphosphonium tetraphenylborate (TPTB) reference electrolyte assumption. The values so obtained have enabled a meaningful separation of the effects of cationic size and charge for the first time in a nonaqueous solvent. As in water, V (o)(M (n+) ) values in DMF are markedly more negative for higher-charged cations due to increasing electrostriction of the solvent. In contrast, ionic charge has a much smaller effect on C p (o)(M (n+) ) in DMF than in water. Ionic volumes in DMF show the expected dependence on size but those of small monatomic monovalent cations and anions imply a significant difference in accessibility of the electron donor and acceptor sites on the DMF molecule. Ionic heat capacities in DMF show a relatively weak dependence on ionic size that, when corrected for charge, is opposite to that in water. Both V (o)(R 4N (+)) and C p (o)(R 4N (+)) in DMF show the usual linear dependence on carbon number but differ from their values in aqueous solution due to the absence of hydrophobic interactions in DMF.

Hydration of Tetraphenylphosphonium and Tetraphenylborate Ions by Dielectric Relaxation Spectroscopy

A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBPh4 and Ph4PCl has been made at solute concentrations of 0.02 < or = c/M < or = 0.82 and 0.20, respectively, and over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) at 25 degrees C. The spectra were best described by a superposition of four Debye processes, consisting of a very small ion-pair contribution with an average relaxation time of about 300 ps, a "slow"-water relaxation at 17 ps, and two bulk-water relaxations at 8 ps and 0.25 ps, respectively. The slow-water process has been assigned to the presence of a sheath of water molecules surrounding BPh4- and Ph4P+, whose structure has been enhanced by its proximity to the bulky hydrophobic phenyl rings. A structure-making effect on the remaining solvent water can also be observed at low concentrations. More importantly, BPh4- and Ph4P+ show almost identical hydration characteristics, which provides indirect support for the use of the tetraphenylphosphonium tetraphenylborate reference electrolyte assumption in deriving single-ion thermodynamic properties.

Solubility and Thermodynamic Transfer Functions of Cesium Dianilinetetraisothiocyanatochromate(III)

The solubilities of cesium dianilinetetraisothiocyanatochromate(III) in water as well as in aqueous methanol, isopropyl alcohol, tert-butyl alcohol and acetonitrile were measured as a function of temperature and solvent composition. The Gibbs energies, enthalpies and entropies of transfer of the salt from water to the given solvents have been evaluated from experimental data. The contribution of [Cr(C6H5NH2)2(NCS)4]- ion to the Gibbs energy of transfer of the investigated salt has been calculated using the tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte assumption.

Solubility and thermodynamic transfer functions of hexa-amminecobalt(III) and tris(ethylenediamine)cobalt(III) hexacyanoferrates(III)

The solubilities of hexaamminecobalt(III) and tris(ethylenediamine) cobalt(III)hexacyanoferrates(III) were measured in water as well as in binary mixtures of water with tert -butyl alcohol and acetonitrile as a function of temperature. The Gibbs energies, enthalpies and entropies of transfer have been evaluated from experimental data. The contribution of [Co(NH 3 ) 6 ] 3+ , [Co(en) 3 ] 3+ and [Fe(CN) 6 ] 3− ions to the Gibbs energies of transfer of the investigated salts have been calculated using the TATB reference electrolyte assumption.

Thermochemical and volumetric properties of aqueous urea systems. Heat capacities and volumes of transfer from water to urea—water mixtures for some 1 : 1 electrolytes at 298.15 K

This paper reports densities, apparent molar volumes and apparent molar heat capacities at 298.15 K for sodium chloride, tetraphenylarsonium chloride and sodium tetraphenylboron in water and aqueous urea solutions containing 5, 10, 20 and 30% urea by weight. Standard-state properties have been calculated from these data which in turn have been used to calculate volumes and heat capacities of transfer for the bulk electrolytes. Single-ion thermodynamic properties have been calculated using the tetraphenylarsonium—tetraphenylboron reference electrolyte assumption. Interpretation of the trends observed in these data are discussed in terms of structural interactions within the system. In addition, densities, apparent molar volumes and apparent molar heat capacities are reported for solutions of urea in water at concentrations up to 16 mol kg–1 at 288.15, 298.15, 308.15 and 313.15 K.

Single-ion enthalpies and entropies of transfer from water to aqueous urea solutions at 298.15 K

In this paper we report enthalpies of solution at infinite dilution [Formula: see text] at 298.15 K for tetraphenylarsonium chloride (Ph4AsCl), sodium tetraphenylborate (NaBPh4), sodium chloride (NaCl), sodium bromide (NaBr), and sodium iodide (NaI) in water and aqueous solutions containing 5, 10, 20, and 30% urea by weight. Enthalpies of transfer from water to aqueous urea solutions are reported. Single-ion enthalpies of transfer [Formula: see text] have been calculated using the tetraphenylarsonium tetraphenylborate, (TATB) reference electrolyte assumption. These single-ion enthalpy data have been combined with single-ion Gibbs functions of transfer [Formula: see text] reported in the literature to obtain single-ion entropies of transfer [Formula: see text] for the urea + water mixed solvent system. The results of this single-ion analysis are discussed in terms of the impact of electrolytes on the structure of aqueous urea solutions.

Limiting partial molar volumes of electrolytes in dimethyl sulfoxide–water mixtures at 298.15 K

Limiting partial molar volumes of electrolytes in several water-dimethyl sulfoxide mixtures, up to xDMSO= 0.1587, have been determined from density measurements at 298.15 K. A reference electrolyte assumption (TATB) has been used in order to obtain single-ion partial molar volumes of transfer from water to DMSO–water mixtures. The influence of DMSO on ΔtV′0i of alkali metals and halide ions is negligible in the highly water-rich region (up to xDMSO≈ 0.04) except for the I– ion. However, when the DMSO composition is greater than xDMSO≈ 0.04, the variation of ΔtV′0i for alkali metals is the reverse to that of halide ions. The results are discussed on the basis of ion–solvent and solvent–solvent interactions using Conway's model.

Deprotonation and transfer energetics of glycine in aqueous mixtures of urea and glycerol from emf measurements at different temperatures

Deprotonation constants, Ka(RH2+) and Ka(RH±), of glycine (RH±) have been determined at five equidistant temperatures ranging from 15 to 35 °C by measuring the emf of galvanic cells comprising Pt/H2 and Ag–AgCl electrodes in aqueous mixtures of protophilic protic urea (UH) and protophobic protic glycerol (GL). Medium effects on deprotonation of the acid: [Formula: see text] have been dissected into transfer free energies [Formula: see text] and entropies [Formula: see text] of the species involved as obtained by measuring the transfer energetics [Formula: see text] of RH± from solubility measurements at different temperatures and of H+ based on tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte assumption determined earlier. The [Formula: see text] values obtained after due correction from the cavity effect based on scaled particle theory (SPT) and electrostatic effects including Born and ion–dipole effects for the charged species involved in the two deprotonation equilibria enable better understanding of the solvent effect on the deprotonation constants. Moreover, the [Formula: see text]–composition profiles are found to exhibit similar characteristic maxima and minima as for simple cations and anions in these solvent systems, thus providing useful information on the structural characteristic of these cosolvents. Keywords: deprotonation energetics, glycine, aqueous urea, aqueous glycerol, EMF measurements.

Single-ion transfer energetics of some ions using tetraphenylarsonium tetraphenylborate reference electrolyte assumption in aqueous mixtures of urea and glycerol

Single-ion transfer free energies [Formula: see text] and entropies [Formula: see text] of some ions from water to aqueous mixtures of urea and glycerol have been determined using the widely used tetraphenylarsonium tetraphenylborate reference electrolyte assumption from solubility and emf measurements of some appropriate electrolytes at five different temperatures (15 to 35 °C). Analysis of [Formula: see text] and [Formula: see text] values of the ions as well as their respective "chemical" effect, [Formula: see text] and [Formula: see text] as obtained after correcting for their cavity and Born-type electrostatic effects, estimated by the scaled particle theory (SPT) and simple Born equation, respectively, show a complex dependence upon solvent composition. Attempts have been made to explain the observed mirror-image entropie behaviour of simple cations and anions in the light of Kundu etal.'s four-step transfer process and to compare the results with those obtained in other aquo-ionic and nonionic systems. Keywords: single ion, transfer energetics, TATB assumption, aqueous glycerol, aqueous urea.

Relative Standard Electrode Potentials of I3−/I−, I2/I3−, and I2/I− Redox Couples and the Related Formation Constants of I3− in Some Pure and Mixed Dipolar Aprotic Solvents

Abstract Standard potentials of I3−/I− and I2/I3− redox couples relative to that of aqueous saturated calomel reference electrode SCE (W), ESCE(w) have been determined in propylene carbonate (PC), N,N-dimethylformamide (DMF), acetonitrile (ACN), and their binary mixtures at 25 °C from potentiometric measurements. The results helped evaluate the standard potentials of the redox couple I2/I− relative to ESCE(w) as well as the related formation constant (Kf) of I3− in these solvent systems. The solvent effects on the formation equilibrium I2+I−\ightleftharpoonsI3− were analyzed in the light of the transfer free energies of I2, ΔGt°(I2), as obtained from solubility measurements of I2 in the solvents, that of I−, ΔGt°(I−), as obtained earlier by use of the widely used TATB reference electrolyte assumption and that of I3−, ΔGt°(I3−), as obtained by subtracting these two contributions from the respective transfer free energies of formation equilibrium in the mixed solvents relative to a chosen reference solvent in each solvent system. The solvation behavior of these individual iodine species viz. I2, I−, I3− was interpreted in terms of involved interaction viz. Born, ion-dipole, ion-induced dipole, dispersion type soft–soft interactions, CTTS complexation and also the cavity effect as computed by the scaled particle theory (SPT).

Ion–ion–solvent interactions in aqueous ionic cosolvent systems. II. Single-ion transfer free energies and entropies using tetraphenylarsonium tetraphenylborate reference electrolyte assumption in aqueous sodium nitrate solvent system

Single-ion tranfer free energies [Formula: see text] and entropies [Formula: see text] of some electrolytes from water to 1, 2, and 4m aqueous NaNO3 solvents have been determined at 25 °C using the widely used tetraphenylarsonium tetraphenylborate (Ph4AsBPh4) reference electrolyte assumption, after due modification for this solvent system. The required [Formula: see text] and [Formula: see text] values of Ph4AsPi, KBPh4, KPi, AgPi, PbPi2, Ag2CrO4, and AgCl where Pi = picrate, were determined by measuring solubilities at 15–35 °C of the solutes except AgCl, the values of which were determined from emf measurements. Analysis of [Formula: see text] and [Formula: see text] values of the ions as well as their respective true interaction effects, [Formula: see text] and [Formula: see text] as obtained after correcting for their cavity effects [Formula: see text] and [Formula: see text] estimated by the scaled particle theory (SPT) and Born-type electrostatic effects, [Formula: see text] and [Formula: see text] computed by simple Born equation, reveals that the behaviour of the ions in this ionic cosolvent system is chiefly guided by one or several effects of ion–ion–solvent, Born and cavity forming interactions. Moreover, a rational explanation has been offered to explain the observed mirror-image entropie behaviour of simple cations and anions in light of Kundu etal.'s four-steps transfer process.

Kinetic solvent effects on acid-catalyzed hydrolysis of sucrose in aqueous mixtures of some protic, aprotic, and dipolar aprotic solvents

Rate constants of acid-catalyzed hydrolysis of sucrose (S) to D-glucose and L-fructose have been determined at 25 °C by optical rotation measurements in aqueous mixtures of protophobic protic glycerol (GL), protophilic protic urea (UH), aprotic dioxane (D), and dipolar aprotic dimethyl sulphoxide (DMSO). Transfer free energies of the substrate sucrose, [Formula: see text] have also been determined in the solvents from solubility measurements. These values as well as those of H+, as obtained earlier by use of the widely used tetraphenylarsonium tetraphenylboron (TATB) reference electrolyte assumption, yielded transfer free energies of the transition state. The observed log (ks/kw) – composition profiles reveal that the rates increase monotonically in GL–water mixtures, that decrease more or less monotonically in UH– and DMSO–water mixtures, and decrease up to 10 mol% D in D–water mixtures, beyond which the values tend to increase. Examination of [Formula: see text]–composition profiles for the different species in each case indicates that the initial and transition state solvation get more or less compensated and the observed rates are dictated by the increased solvation of H+ in aqueous UH, DMSO, and D co-solvent systems. But in GL–water mixtures the decreased solvation of the transition state compared with the initial state is overcome by the decreased solvation of H+, thus resulting in the gradual enhancement of the rates of the reaction. The observed linearity of the correlative plots of −δ(ΔG≠) [= RT ln (ks/kw)] vs. [Formula: see text] with distinctly different slopes in the two cases also substantiates the relative importance of H+ solvation in dictating the rates of the reaction in these widely different aqueous co-solvents.

Medium effects on deprotonation of phthalic and biphthalic acids in aqueous binary mixtures of some protic, aprotic, and dipolar aprotic cosolvents

Deprotonation constants of phthalic acid (H2A), (Ka)HzA, and biphthalic acid (HA–), (Ka)HA–, have been determined at 25 °C by measuring the e.m.f.s of galvanic cells comprising glass and Ag–AgCl electrodes in aqueous mixtures of organic cosolvents of different chemical nature, viz. protic glycerol (GL), aprotic dioxane (D), protophobic dipolar aprotic acetonitrile (ACN), and protophilic dipolar aprotic dimethyl sulphoxide (DMSO). Medium effects on deprotonation of the acids: δ(ΔG°diss,)=2.303 RT[p(sKa)– p(wKa)] have been dissected into transfer free energies ΔG°t of the species involved by evaluating ΔG°t of the uncharged acid (H2A) from the measured solubilities of the acid and using ΔG°t of H+ based on the widely used tetraphenylarsonium tetraphenylboride (TATB) reference electrolyte assumption, as reported earlier for the solvents. The contributions of the different species involved in the protolytic equilibria, viz. H+, acids (H2A or HA–), and their respective conjugate bases (HA– or A2–) are discussed in terms of their solvation behaviour as guided by the ‘acid-base’, dispersion, structural, and electronic characteristics of the acid–base species and of the cosolvent molecules and their aqueous mixtures, besides the Born-type electrostatic interactions on the ionic acid–base species.

ChemInform Abstract: TRANSFER FREE ENERGIES OF FLUORIDE ION IN AQUEOUS MIXTURES OF SOME ORGANIC SOLVENTS

AbstractDie Freien Standardenergien für den Transfer von KF aus H2O in wäßrige Gemische von DMSO, DMF, MeCN, 1,2‐Dimethoxyethan (DME) und 2‐Methoxyethanol (ME) werden bei 25°C aus EMK‐Messungen an der Doppelkette A bestimmt.

Transfer Free Energies of Fluoride Ion in Aqueous Mixtures of Some Organic Solvents

Abstract Standard free energies of transfer, ΔGt°, of potassium fluoride (KF) from water to aqueous mixtures of dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), acetonitrile (ACN), 1,2-dimethoxyethane (DME), and 2-methoxyethanol (ME) have been determined at 25 °C from emf measurements performed on the double cell: Pb(Hg)–PbF2/KF(m), solvent/K(Hg)/KF(m), water/PbF2–Pb(Hg). ΔGt° values of F− were obtained from these values using the corresponding values of K+, as obtained earlier by use of tetraphenylarsonium tetraphenylborate reference electrolyte assumption. In each solvent system ΔGt°(F−) values are found to be increasingly positive with cosolvent composition reflecting the pronounced destabilization of F− and their relative order : DME&amp;gt;DMSO≥DMF&amp;gt;&amp;gt;ACN≈ME conforms to what is expected from the relative ‘aproticity’ of the dipolar aprotic cosolvents and that induced in the protic ME by the possible intramolecular H-bonding. The observed larger destabilization of F− compared to OH− in ME–water system has been attributed to the H-bonding effect of the protic cosolvent ME and the reverse behaviour in DME–water and DMSO–water systems to the absence of such effect of these cosolvents. Moreover, tests of Feakins-type extrapolation for assigning individual ion contribution using ΔGt°(KF) values along with those of other potassium halides, provided some important reflections on the inadequacy of such plots made without the data points of F−.

Ion-solvent interactions in dimethylformamide + water mixtures

Standard Gibbs energies of transfer, Δ G° t , of MCl (M = Li, Na, K, Rb and Cs) and K X ( X = Br and I) have been determined by use of the double cells comprising M(Hg) and Ag XAg electrodes in some aqueous mixtures of DMF at 25°C. These values were dissected into individual ion contributions using TATB reference electrolyte assumption, as obtained by measuring the solubility products of the salts viz. KPic, KBPh 4 and Ph 4AsPic. The observed increasingly positive magnitudes of Δ G° t of the halide ions and the increased negative magnitudes of the cations including H +, reflect the well known anion-destabilization and the larger “basicity” and cationotropism of the aqueous mixtures of this co-solvent. And the observed distinctly flat regions of Δ G° t curves of cations over an intermediate composition are attributable to strong intercomponent interactions. Comparison of the results with those in DMSO—water are ACN—water mixtures reveals that the solvating characteristics of DMF—water are somewhat similar to that of DMSO—water but different from that of ACN—water mixtures. Moreover, while the observed relative behaviour of Pic − are found to be guided by the combined effects of dispersion interactions and anion destabilisation of these co-solvents, that of the large-sized tetraphenyl ion is, however, guided by the combined effects of dispersion interactions as well as the “cavity-forming” interactions as estimated in the light of scaled particle theory.

Medium effects for single ions in acetonitrile and ethanol-water solvents based on reference-electrolyte assumption

Medium effects for single ions in acetonitrile and ethanol-water solvents based on reference-electrolyte assumption