Ionic species hydration

Amine oxides show either nonionic or cationic behavior in aqueous solution depending on pH. In acid solution the cationic form (R2N" OH) is observed (2) while in neutral and alkaline solution the nonionic form predorninates as the hydrate R NO H2O. The formation of an ionic species in the acidic pH range stabilizes the form generated by the most studied commercial amine oxide, dimethyldodecylamine oxide (6). 

Reactions in chloroaluminate(III) salts and other related binary salts often proceed smoothly to give products. However, it should be noted that these salts are water-sensitive and must be handled under dry conditions. They react with water to give hydrated aluminium(III) ionic species and HCl. When a reactant or product contains a heteroatomic functional group, such as a ketone, a strong ketone/alumini-um(III) chloride adduct is formed. In these cases, this adduct can be difficult to separate from the ionic liquid at the end of a reaction. The isolation of the product often... 

A term used in electrostatic descriptions of ions to denote the continuous electric charge density [p(r)] surrounding an ionic species. On average, an ion will be surrounded by a spherically symmetrical distribution of counterions that form its ion atmosphere. See Hydration Atmosphere... 

In a solid-gas reaction involving a molecular crystal, the reactants are respectively the molecules in the crystalUne solid and the molecules in the gas phase and the product is the product crystal, which can be crystalUne or amorphous. Vapour uptake to generate a solvate crystal (e.g. hydration) is a related process. In fact the difference between a crystal solvation process and a solid-gas reaction leading to new molecular/ionic species is mainly in the energetic scale of the processes and in the fact that in solvation processes, molecules retain their chemical identity. On this premise there is a relevant analogy between the uptake of smaU molecules by a nanoporous material [16] and the reaction between a molecular crystal and molecules to yield a co-crystal or a salt (e.g. acid-base... 

In the case of ionic species it proved advantageous to include at least two layers of hydration in the entire QM region. For composite solutes this condition leads to an enormous computational effort. However, as these species are in general less polarizing than ions, the size of the core zone can be chosen to include the solute and eventually a part of the first hydration layer only. 

In the second item above, the presence of bound and free water molecules was noted. Both bound ions and ionic surfactant groups are hydrated to about the same extent in the micelle as would be observed for the independent ions. The dehydration of these ionic species is an endothermic process, and this would contribute significantly to the AH of micellization if ion dehydration occurred. In the next section we discuss the thermodynamics of micellization, but it can be noted for now that there is no evidence of a dehydration contribution to the AH of micelle formation. The extent of micellar hydration can be estimated from viscosity... 

Ionic and hydrated radii o< several ions. Smaller, more highly charged ions bind water molecules more tightly and behave as larger hydrated species.3... 

Often more complex situations arise in which additional tautomers or other forms arise via pH-independent reactions. These can all be related back to the reference ionic species by additional ratios R, which may describe equilibria for tautomerization, hydration, isomerization, etc. (Eq. 6-82).76 In the case illustrated, only one of the ratios, namely R2 or R3, is likely to be a tautomerization constant because, as a rule, H2P and P will not have tautomers. Equations analogous to Eqs. 6-76 to 6-82 can be written easily to derive Kc, K0 and any other microscopic constants desired from the stoichiometric constants plus the ratios R, to R4. While it is easy to describe tautomerism by equations such as Eqs. 6-76 and 6-82 it is often difficult... 

In the opinion of many authors, charge transfer in polymers occurs by an ionic mechanism. However, the evidence in favor of this mechanism is somewhat tenuous and in many cases could well be interpreted in terms of conduction via an electronic mechanism. Part of the confusion has arisen because, in many cases, surface and electrode effects have not been eliminated, the degree of hydration is not known, it is not certain whether the ion moves bodily through the material or whether the migration of charge occurs by exchange between an ionic and non-ionic species. Finally, the nature of the supposed ionic species is not known. 

The ionic species corresponding to the four oxidation states of plutonium vary wifli the acidity of the solution. In moderately strong < one-molar) acid the species are Pu11, Pu4+, PuO ,1, and PuO 2 E The 10ns are hydrated but it is not possible at present to assign a definite hydration to each ion. The potential scheme of these ions in one-molar perchloric acid is tile following ... 

The effect of solvent change on an equilibrium involving non-ionic species is expected to be small. While specific effects do show up, this expectation is realized in the hydration of sym-dichloroacetone in dioxane-water mixtures (Bell and McDougall, 1960) and in the formation of acetone cyanohydrin in various solvents (Stewart and Fontana, 1940) (Table 7). 

Partial molar volumes of electrolytes may present an additional difficulty if the partial molar volumes of individual constituent ions are needed. The subject has been dealt with as part of a valuable discourse on metal ion solvation.158 For species in water and some other solvents, the reference point for calculation of other partial molar volumes of single ions is the partial molar volume of the solvated proton, although there have been different views on what this value should be.159 However, the variation in values is not large and the consequence of choice of value does not have a huge impact particularly for large ionic species. Theoretical models of partial molar volumes of hydrated ions have been developed in order that estimates of them can be calculated. 160-162... 

When water comes into contact with the cement (stage I), wetting of the highly hygroscopic cement particles and the solubilization of a variety of ionic species, e.g. Na+, K+, Ca++, S04-, OH-, by complete or selective solubilization (surface hydrolysis) of the various phases present in cement occurs. Surface hydrolysis quickly leads to the formation of a thin layer of both amorphous and gel products. Beyond the initial solubilization phenomena, the formation of any of the solid hydration products (Table 7.31) will be governed by nucleation processes which may occur homogeneously from the solution phase or heterogeneously at a solid-solution interphase [64, 125],... 

C. Curutchet, A. Bidon-Chanal, I. Soteras, M. Orozco and F. J. Luque, MST continuum study of the hydration free energies of monovalent ionic species,. /. Phys. Chem. B, 109 (2005) 3565-3574. 

The reaction occurs at the surface of the electrode (Fig ). The electroactive ion diffuses to the electrode surface and adsorbs (attaches) to it by van der Waals and cou-lombic forces. In doing so, the waters of hydration that are normally attached to any ionic species must be displaced. This process is always endothermic, sometimes to such an extent that only a small fraction of the ions be able to contact the surface closely enough to undergo electron transfer, and the reaction will be slow. The actual electron-transfer occurs by quantum-mechanical tunnelling. 

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