Highly concentrated ionic solutions

However, for more complex fluids such as high-polymer solutions and concentrated ionic solutions, where the range of intemiolecular forces is much longer than that for simple fluids and Nq is much smaller, mean-field behaviour is observed much closer to the critical point. Thus the crossover is sharper, and it can also be nonmonotonic. 

Seawater has high concentrations of solutes and, hence, does not exhibit ideal solution behavior. Most of this nonideal behavior is a consequence of the major and minor ions in seawater exerting forces on each other, on water, and on the reactants and products in the chemical reaction of interest. Since most of the nonideal behavior is caused by electrostatic interactions, it is largely a function of the total charge concentration, or ionic strength of the solution. Thus, the effect of nonideal behavior can be accoimted for in the equilibrium model by adding terms that reflect the ionic strength of seawater as described later. 

In 1988, a version of PHREEQE was written including PITZER equations for ionic strengths greater 1 mol/L thus applicable for brines or highly concentrated electrolytic solutions (PHRQPITZ, Plummer et al. 1988). PHREEQM (Appelo Postma 1994) included all options of PHREEQE and additionally a one-... 

At very high concentrations of the ionic solutions, the quasilattice model of Braunstein is useful wherein a highly concentrated electrolyte solution is considered to be a solution of water in fused salts (24) (26). 

Osmotic pressure creates some critical problems for living organisms. Cells typically contain fairly high concentrations of solutes, that is, small organic molecules and ionic salts, as well as lower concentrations of macromolecules. Consequently, cells may gain or lose water because of the concentration of solute in their environment. If cells are placed in an isotonic solution (i.e., the concentration of solute and water is the same on both sides of the selectively permeable plasma membrane) there is no net movement of water in either direction across the membrane (Figure 3.14). For example, red blood cells are isotonic to... 

One can interpret this as signifying that ion exchange equilibria depend on the differences in the properties of the ions themselves rather than on any specific interaction with the resin. Ionic activity coefficients of ions of the same charge are very similar to one another, but their activity coefficients in the resin phase are not. Even though it is not possible to determine the coefficients of the cations in the resin phase directly, the resemblance of the resin phase to a highly concentrated electrolyte solution permits the comparison of experimentally determined values with the... 

A High-Temperature, High Pressure OsciUating-Disk Viscometer for Concentrated Ionic Solutions, Bunsen-Ber. Phys. Chem., 84 (1980), 1255. 

Macdonald J.R., L.D.P. A flexible procedure for analyzing impedance spectroscopy results— description and illustrations. Solid State Ionics 1987 24 61-79 Maissel L.I. Electrical properties of metallic thin films. In Handbook of Thin Film Technology, Maissel L.I., Glang R., ed. New York McGraw-Hill, 1970, pp. 13/11—33 Matsuda H., Mizushima T, Kuwabara M. Low-temperature synthesis and electrical properties of semiconducting BaTiOs ceramics by the sol-gel method with high concentration alkoxide solutions. J. Ceram. Soc. Jap. 1999 107 290-292... 

Inaccuracies arise at modest electrolyte concentrations because the concentrations of ions predicted within an ionic atmosphere are imrealistic if a finite ionic radius is not considered. The assumption of a finite ionic radius leads to the extended Debye-Hiickel limiting law. This is still inaccurate for concentrated ionic solutions because the depletion of solvent molecules due to solvation shells makes the assumption of zero ion-solvent interaction highly inaccurate. Only empirical formulas such as the Robinson-Stokes or Pitzer equations are able to address this issue. Most well-supported electrolyte solutions have behaviours in this latter regime. 

Another approach to matrix matching, which does not rely on knowing the exact composition of the sample s matrix, is to add a high concentration of inert electrolyte to all samples and standards. If the concentration of added electrolyte is sufficient, any difference between the sample s matrix and that of the standards becomes trivial, and the activity coefficient remains essentially constant. The solution of inert electrolyte added to the sample and standards is called a total ionic strength adjustment buffer (TISAB). 

A solution containing a relatively high concentration of inert electrolytes such that its composition fixes the ionic concentration of all solutions to which it is added. 

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