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Rudolph, Wolfram W.; Brooker, M. H.; Tremaine, Peter R.

doi:10.1023/a:1022691117630

Cited by 93 publications

(71 citation statements)

References 5 publications

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“…As a result, unlike the 1 : 40 (298 K) system, the structure of this solution is determined by contact ion pairs. The fact that ion association is enhanced with temperature is nicely consistent with the available data for halide ions and oxygen-containing anions [37,38].…”

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confidence: 88%

D-Structure of Aqueous Solutions of Cobalt(II) Nitrate at 298 and 323 K by X-Ray Diffraction

2005

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Aqueous solutions of cobalt(II) nitrate with 1 : 15, 1 : 25, and 1 : 40 mole ratios at 298 and 323 K were studied by the X-ray diffraction. As the solution concentration decreases, ion triads (1 : 15) pass into contact ion pairs (1 : 25) and then to independently hydrated ions (1 : 40). The structural variations are accompanied by increase in a number of water molecules in the second coordination sphere of the cations and in the hydration shell of the anions. Heating produces destruction of ion triads in the 1 : 15 solution and ion association in the 1 : 40 solution. The structure of all the solutions at 323 K is characterized by a system of contact ion pairs. The structure of concentrated aqueous solutions of electrolytes attracts considerable attention of researchers involved in the fundamental and applied science. Correlations of the trend in structure formation in aqueous electrolyte systems with the chemical nature of ions and solution concentration have been revealed [1]. Recently polythermal studies of such solutions have gained special importance [234]. To obtain statistical data on quantitative characteristics of aqueous electrolyte solutions and to extend the body of experimental information, in the present work we performed an X-ray diffraction study of aqueous solutions of cobalt(II) nitrate at various mole ratios and temperatures. The Co + ion is a complex-forming ion, and a series of X-ray researches have been devoted to its complex formation in solutions of cobalt(II) chlorides and bromides. The aim of the present work was to study structural aspects of ion hydration in solutions, and, therefore, we chose nitrate ions as counterions not inclined to complex formation.In early works [5, 6] on the basis of measuring viscosity of aqueous CoSO 4 solutions it was noted that Co 2+ ions reinforce water structure in a wide concentration range. Kinetic studies on oxygen exchange between nitrate ions and water molecules in aqueous solutions of Co(NO 3 ) 2 at concentrations close to the boundary of complete hydration revealed a twolayer hydrate surrounding [7,8]. In the crystal hydrates Co(NO 3 ) 2 . 2H 2 0 and Co(NO 3 ) 2 . 4H 2 0, cobalt ions are surrounded by six oxygen atoms at distances of 0.205130.2124 nm, of which two atoms belong to nitrate ions (0.206030.2097 nm) and the other two in the first case and four in the second, to water molecules [9]. The octahedral coordination of water molecules around the cation in concentrated aqueous solutions of cobalt(II) halides [10312] and sulfate [13] was revealed by X-ray diffraction analysis, the Co 2+ 3 OH 2 distances varying within 0.20730.216 nm. The formation of contact ion pairs by counterions in CoCl 2 solutions of various concentrations was established [11,14]. Aqueous solutions of CoCl 2 : nH 2 O (n = 6, 4, 2) at various temperatures (298, 313, 328, and 343) were studied by X-ray diffraction. In octahedral cobalt(II) complexes, the Co3O and Co3Cl distances were found to be 0.211 and 0.240 nm, respectively [15]. The number of Co3Cl contacts in saturated...

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confidence: 88%

D-Structure of Aqueous Solutions of Cobalt(II) Nitrate at 298 and 323 K by X-Ray Diffraction

2005

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“…Mean activity coefficient data of ZnSO 4 in water at 25 • C was taken from Robinson and Stokes [29]. The solubility of ZnSO 4 in pure water and in H 2 SO 4 solution was taken from Linke and Seidell [26], and Rudolph et al [30]. As far as the solubility of oxygen in pure water and electrolyte systems, the data were mainly from the work of Battino [31], Narita et al [20], and Hayduk [32].…”

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Thermodynamic equilibrium of the O2–ZnSO4–H2SO4–H2O system from 25 to 250°C

Liu

Papangelakis

2005

Fluid Phase Equilibria

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“…[32,33] Perhaps the small effects observed (except for Li ) are due to 2SIP but this runs counter to conventional views on vibrational spectroscopy. Clearly, further studies are required to resolve this matter.…”

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confidence: 91%

“…Although the authors did not address the hydration state of their species specifically, it is reasonable to assume that they were referring to CIPs (inner sphere complexes), since SIP and 2SIP cannot normally be observed from studies of ligand vibrations. [32,33] The first point to make about these measurements [21] is that they were made in mixed electrolyte solutions, in order to obtain the desired concentration ratios, and thus may not be directly comparable with the present measurements. Secondly, the effects, although systematic, are extremely small (except for solutions containing Li ).…”

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Hydration and Ion Pairing in Aqueous Sodium Oxalate Solutions

et al. 2003

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Dielectric spectra have been measured for aqueous sodium oxalate solutions up to the saturation concentration (0.04 < or = c[mmol L-1] < or = 0.25) at 25 degrees C over the approximate frequency range 0.2 < or = v [GHz] < or = 20. The spectra exhibit a process at about 1 GHz associated with the presence of ion pairs, in addition to the dominant solvent relaxation process at about 18 GHz. Detailed analysis of the solvent dispersion amplitude indicates that the oxalate ion is highly hydrated but that its solvation sheath is "fragile", decreasing quickly with increasing solute concentration. The NaOx(aq)- ion pair is shown to be of the double-solvent-separated (2SIP) type, with an infinite dilution association constant KA = 1.04 +/- 0.02. Analysis of the ion-pair relaxation time as a function of solute concentration gave rate constants for the formation (k12 = (7.3 +/- 0.4) 10(9) L mol-1 s-1) and dissociation (k21 = (6.7 +/- 0.5) 10(8) s-1) of the ion pair. These values are reasonably close to the diffusion-controlled values predicted by the Eigen theory, consistent with a 2SIP structure for the ion pair.

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Cited by 93 publications

References 5 publications

D-Structure of Aqueous Solutions of Cobalt(II) Nitrate at 298 and 323 K by X-Ray Diffraction

D-Structure of Aqueous Solutions of Cobalt(II) Nitrate at 298 and 323 K by X-Ray Diffraction

Thermodynamic equilibrium of the O2–ZnSO4–H2SO4–H2O system from 25 to 250°C

Hydration and Ion Pairing in Aqueous Sodium Oxalate Solutions

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