Ionic hydrated

The solute-solvent interaction in equation A2.4.19 is a measure of the solvation energy of the solute species at infinite dilution. The basic model for ionic hydration is shown in figure A2.4.3 [5] there is an iimer hydration sheath of water molecules whose orientation is essentially detemiined entirely by the field due to the central ion. The number of water molecules in this iimer sheath depends on the size and chemistry of the central ion ... 

Straatsma, T.P, Berendsen, H.J.C. Free energy of ionic hydration Analysis of a thermodynamic integration technique to evaluate free energy differences by molecular dynamics simulations. J. Chem. Phys. 89 (1988) 5876-5886. 

G Hummer, LR Pratt, AE Garcia. Eree energy of ionic hydration. J Phys Chem 100 1206-1215, 1996. 

Heinzinger, K. Palinkas, G. (1987). In Kleeberg, H. (ed.) Interactions of Water in Non-ionic Hydrates. Berlin Springer-Verlag. 

Robinson, G. W., Thistlethwaite, P. J. Lee, J. (1986). Molecular aspects of ionic hydration reactions. Journal of Physical Chemistry, 90, 4224-33. 

It was found in later work that it is precisely the idea of ionic hydration that is able to explain the physical nature of electrolytic dissociation. The energy of interaction between the solvent molecules and the ions that are formed is high enough to break up the lattices of ionophors or the chemical bonds in ionogens (for more details, see Section 7.2). The significance of ionic hydration for the dissociation of electrolytes had first been pointed out by Ivan A. Kablukov in 1891. 

Ionic solvation is interaction between ions and solvent molecules that leads to the formation of relatively strong aggregates, the solvated ions. In aqueous solutions the terms ionic hydration and hydrated ions are used as weU. 

The number of binding sites can be determined in this model by a plot of d Ink /dlnm at constant temperature, pH, and ion valency. To do that, it may be assumed that dlny /dlnm is approximately zero. The actual value is -0.04 for 0.1 to 0.5 M sodium chloride and less at lower concentrations. To a first approximation, the stoichiometry of water molecules released by binding protein could be determined from the slope of the plot of dink /dlnm vs. m. However, especially at low salt concentration and near the isoelectric point, the slope of such plots is nonlinear. The nonlinearity may be due to hydrophobic interaction between stationary phase and protein or a large change of ionic hydration on binding.34... 

Conway, B. E., Ionic Hydration in Chemistry and Biophysics, Elsevier, Amsterdam, 1981. 

Hummer, G. Pratt, L. Garcia, A. E., Free energy of ionic hydration, J. Phys. Chem. 1996,100, 1206-1215... 

T. P. Straatsma and J. C. Berendsen, Free energy of ionic hydration Analysis of a... 

In an early study, Mauritz et al. investigated anion—cation interactions within Nation sulfonate membranes versus degree of hydration using FTIR/ ATR and solid state NMR (SSNMR) spectroscopies. An understanding of the dynamic ionic—hydrate molecular structures within and between the sulfonate clusters is essential for a fundamental understanding of the action of these membranes in ion transport. This information can be directly related to the equilibrium water swelling that, in turn, influences molecular migration. 

The Na NMR parameters of Nafion are not greatly affected by changing EW in the range of water content where valid comparisons are possible. " and this reflects the short-ranged nature of these dynamic ionic—hydrate structures. 

The calculation may be based on a recently evolved theoretical electrostatic model for ionic hydration (7). 

Improved theoretical models for ionic hydration and the variations with temperature of the solvating properties of water so that the free energies can be more accurately extrapolated to elevated temperatures. These models must progress from simple monovalent ions to polyvalent and complex ions, e.g. Cs+, Sr +, Pu " ", ions of Tc, I, etc. 

The process of hydration of an ion refers to the conversion of one mole of the gaseous ions under standard conditions at a pressure of I bar to the hydrated ions at a molar concentration of 1 mol dm-3. The process may be divided into two parts. These are the compression of the one mole of gaseous ions into a volume of 1 dm3 followed by the interaction of the ions with water to produce the hydrated ions. Assuming ideal gas behaviour, the compression of one mole of a gas at standard pressure and at 298.15 K into a volume of I dm3 requires the expenditure of enthalpy given by RT ln(24.79/l. 0) = +7.96 kJ mol -. The quoted values of ionic hydration enthalpies include a contribution from the compression of the gaseous ions and the enthalpy changes associated with the hydration process are given by the equation ... 

As to the first of these, I have elsewhere [10] discussed the classification of the ionic hydrates, which can best be taken on a geometrical basis according to the way the water molecules are grouped, In the first group the water molecules occur singly or in clusters they may be... 

Concentrated solutions are strongly affected by ionic hydration. Its strength depends upon ionic radius and charge, therefore it is in general stronger for cations than anions. K2S04 and MgS04 both yield 3 ions,... 

Thermal anomalies ( kinks ) in the properties of water and aqueous solutions appear to be manifestations of higher-order phase transitions in structured elements of water. Some concentration-dependent anomalies are also described and discussed in terms of (a) the occurrence of discrete structural units of water in the unaffected solvent, (b) the possible separate existence of somewhat similarly structured units in the ionic hydration atmospheres, and (c) overlapping of large (but not necessarily structured) hydration atmospheres. 

These observations indicate a decreased hydration interaction between water and the ammonium ion (or its derivatives) as compared to the sodium ion. The findings are confirmed by unpublished data131 regarding AOT micelles in isooctane saturated with D20. The smallest aggregates (micelles) observed with the photon correlation technique are smaller which would follow from the fact67 that the heats of ionic hydration are smaller and the hydrogen bonds (OD. .. X) to a foreign acceptor (X) are weaker in D20 compared to H20. 

Blandamer and Symons (57) assumed in their work that the free energies of hydration of Rb+(g) and Cl (g) were identical, since the two ions have crystal radii of the same magnitude. Jain (58) has also applied the radii to calculate absolute free energies of ionic hydration. His treatment is in category (ii) and is based on the model developed by Frank and coworkers (59). The equation used is similar to that employed by Stokes (60) and utilizes calculated van der Waals radii of the ions as well as the crystal radii. To obtain the best agreement it was necessary to assume that the effective dielectric constant in water is 2.7. 

Fig. 10. Ionic hydration energies plotted against the lull line of the Born equation...

The purpose of this paper is to calculate the electrochemical potential and the double layer repulsion using a lattice model, applicable to hydrated ions of different sizes, that accounts for the correlation between the probabilities of occupancy of adjacent sites. As the other lattice models,4-7 this model accounts only for the steric, excluded volume effects due to ionic hydration. In feet, short-ranged electrostatic interactions between the ions and the dipoles of the water molecules, as well as the van der Waals interactions between the ions and the water molecules, are responsible for the formation of the hydrated ions. The long-ranged interactions between charges are taken into account through an electrostatic (mean field) potential. The correlation between ions is expected to be negligible for sufficiently low ionic concentrations. 

In this brief review of salt solutions, we start by examining ionic hydration. We then examine from the standpoint of ion-ion interactions the properties of real solutions and how these are affected by ionic hydration (Blandamer, 1970). 

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