Effective ionic strength

In this work the concepts of ionic medium, effective ionic strength and free versus total activity coefficients are examined. Then they are applied to the study of permissible and incorrect translations of equilibrium constants from one medium to another. 

It is important to realize that one must take into consideration ion association of the ionic media electrolytes because it affects the effective ionic strength (2). This in turn changes the activity coefficients of the ions under study. The effective ionic strength, Ie, of a 2-1 electrolyte CA2 which associates is given by... 

A comparison of experimental results with those calculated from the Fuoss (2) theory is presented in Table I. The theory 1s only valid approximately so that the order of magnitude agreement is fairly good, except in the cases of MgC03° and CaC03 . Stoichiometric association constants K are then obtained from the activity coefficients, expressions for K, and from equations for the conservation of mass. The latter express the total concentration of a given ion as the sum of the concentrations of the free ion and of the ion-pairs. Values of K and of the activity coefficients of free ions in ionic media depend only upon the effective ionic strength as is shown later. 

Y+)p depends)(only upon the effective ionic strength of the medium. Thus, ksp", K, and e can be determined in one ionic... 

The concepts of ionic media, free and total activity coefficients, properties of equilibrium constants, and effective Ionic strength to be used here were examined in an earlier paper in this volume. 

MICROTUBULE ASSEMBLY KINETICS KINETIC ELECTROLYTE EFFECT IONIC STRENGTH KINETIC EQUIVALENCE KINETIC AMBIGUITY KINETIC HALDANE RELATIONSHIPS HALDANE RELATIONSHIPS... 

There are a number of assumptions made in the model that are questionable, and these are probably responsible for the discrepancy between the predicted and observed behaviour of the slurries. For example, the steric contribution has been calculated assuming that the adsorbed layer has a well-defined thickness. For adsorbed polymers this is unlikely to be the case, as the volume fraction profile of the polymer will decay gradually as a function of distance from the surface. Furthermore, it was assumed that the effective ionic strength in the adsorbed polymer layer is the same as in solution. However, this also is unlikely since one of the main components of the solution ionic strength is the polymer itself, and unadsorbed polymer will be excluded from the adsorbed layer. Finally, the connectivity of the charged groups on the polymer was not considered, so its contribution to ionic strength may have been overestimated. 

We have made no systematic studies of ionic strength effects. Ionic strength does not seem important in the catalytic hydrolysis of the acylnitrophenolates, which carry no charge. There are substantial salt effects in the decarboxylation reaction with nitrobenzisoxazole, which is an anionic substrate. These may reflect general ion cloud effects or anionic competition for binding to the polymer. 

Table A6.2 includes historical information on the comparison of ion activity coefficients at the effective ionic strength of seawater. Activity coefficients measured in single salt solutions are compared with those measured in seawater and those calculated from an association model. We have to distinguish between total activity coefficients (cf. equations 3 and 4)...

Compute the total or stoichiometric and effective ionic strengths, and corresponding total- and free-ion activity coefficients of Ca and SO in pure water saturated with gypsum at 25"C. It is given that the solubility product of gypsum, and that at gypsum saturation... 

The effective ionic-strength approach assumes the existence of ion pairs, thus the mass-balance equations are... 

Tabulated here are concentrations of free species and ion pairs expressed as percentages of the total concentrations given above assuming the ion pair model and effective ionic strength. 

The stoichiometric or total ionic strength (/,) is computed ignoring solution ion pairs, whereas the effective ionic strength takes ion pairs into account. /, is greater than I,. Why Ion activities (a,) must be the same, whichever ionic strength model is used, so that n, = y,m, = 7/>np where the subscript t denotes total ion values that apply when /, is used. Subscript/indicates free ion values should be used when is employed. Explain and contrast the two approaches with an example. 

The osmotic pressure of solutions and especially the osmotic pressure in the boundary layer reduces the effective transmembrane pressure. To estimate the possible effect, ionic strength and osmotic pressure values for various salt solution compositions are summarised in Table 7.22. 

It was mentioned above that for 1 1 electrolytes, the concentration limit for the stability of an electrostatically stabilized dispersion is an ionic strength in the dispersion medium of order I0 M. This concentration is not very high by way of specific examples, we recall that the effective ionic strength of many biological systems is comparable to this (e.g. an isotonic solution of potassium chloride is ca 016 M and sea water has an ionic strength of order 0-6 M). 

Exert the minimum osmotic effect, ionic strength, and pH. 

Considering the binding effect, ionic strength effect, size dependence, junction potential and iR drop as well as the overpotential, r), the half maximum potential observed can be expressed as... 

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