Indifferent electrolyte effect

Conversely, the addition of some other ions can promote solubility by the indifferent electrolyte effect. The use of hydrophilic molecules such as the hydroxyacids (e.g. citrate, tartaric) or aromatic carboxylic acids (e.g. benzoic) can create cavities in the water structure thereby promoting solubilization. Many salt formers increase drug solubility by this type of mechaiusm. Citrate buffers and sodium benzoate, the latter often used in formulations as an antimicrobial preservative, are known to enhance the solubility of a number of drugs. 

As stated above, the indifferent electrolyte effect is altered and possibly enhanced when the ions of that electrolyte undergo hydrolysis in the aqueous... 

The effect of the charge as well as that of the indifferent electrolyte, then, is contained in the term in brackets. A numerical calculation is probably the easiest way to examine this effect. This is illustrated in the following example. 

These results show more clearly than Fq. (8.126)-of which they are special cases-the effect of charge and indifferent electrolyte concentration on the osmotic pressure of the solution. In terms of the determination of molecular weight of a polyelectrolyte by osmometry. ... 

For sparingly soluble salts of a strong acid the effect of the addition of an acid will be similar to that of any other indifferent electrolyte but if the sparingly soluble salt MA is the salt of a weak acid HA, then acids will, in general, have a solvent effect upon it. If hydrochloric acid is added to an aqueous suspension of such a salt, the following equilibrium will be established ... 

In potentiometric measurements the simplest approach to the liquid-junction problem is to use a reference electrode containing a saturated solution of potassium chloride, for example the saturated calomel electrode (p. 177). The effect of the diffusion potential is completely suppressed if the solutions in contact contain the same indifferent electrolyte in a sufficient... 

If the effect of the electrical double layer is neglected (e.g. at higher indifferent electrolyte concentrations), the rate constant of the cathodic reaction is approximately given by the equation... 

Ideal potentiometric measurements, especially in analytical chemistry, would require that the potential of the reference electrode be fixed and known, and that the composition of the studied solution affect only the potential of the indicator electrode. This would occur only if the liquid-junction potential could be completely neglected. In practice this situation can be attained only if the whole system contains an indifferent electrolyte in a much larger concentration than that of the other electrolytes, so that the concentration of a particular component in the analysed solution, which is not present in the reference electrode solution, has only a negligible effect on the liquid-junction potential Such a situation rarely occurs, so that it is necessary to know or at least fix the liquid junction potential... 

Use these data and the Debye-Hiickel theory of electrolyte nonideality to criticize or defend the following proposition Indifferent electrolytes always inhibit the rates of ion combination reactions because the activity coefficients are fractions. The data for CTABr show an enhancement of rate so this cannot be due to an activity effect. In these data, the k s for pure water and aqueous NaCl are essentially identical, so no activity effects operate in the absence of micelles either. 

Of the various quantities that affect the shape of the net interaction potential curve, none is as accessible to empirical adjustment as k. This quantity depends on both the concentration and valence of the indifferent electrolyte, as shown by Equation (11.41). For the present we examine only the consequences of concentration changes on the total potential energy curve. We consider the valence of electrolytes in the following section. To consider the effect of electrolyte concentration on the potential energy of interaction, it is best to use the more elaborate expressions for interacting spheres. Figure 13.8 is a plot of ne, for this situation as a function of separation of surfaces with k as the parameter that varies from one curve to another. 

If counter ions are adsorbed only by electrostatic attraction, they are called indifferent electrolytes. On the other hand, some ions exhibit surface activity in addition to electrostatic attraction because of such phenomena as covalent bond formation, hydrogen bonding, hydrophobic and solvation effects, etc. Because of their surface activity, such counter ions may be able to reverse the sign of because the charge of such ions adsorbed exceeds the surface charge. 

Potentiometric titration denotes a change in the pH of any given clay or soil suspension as a function of base or acid added. Generally, three types of potentiometric titration curves are produced (Fig, 3.36). The first type, represented by Figure 3.36a, shows a common crossover point for all three potentiometric curves, representing three different concentrations of an indifferent electrolyte (i.e, NaN03). The crossover point of the titrations is known as the point of zero salt effect (PZSE). The intercept of the dotted line with the titration lines is known as the pH of zero titration (PZT). For a pure oxide,... 

A procedure for the elimination of liquid junction potentials, suggested by Nemst (1897), is the addition of an indifferent electrol3rte at the same concentration to both sides of the cell. If the concentration of this added substance is greater than that of any other electrolyte, the former will carry almost the whole of the current across the junction between the two solutions. Since its concentration is the same on both sides of the boundary, the liquid junction potential will be very small. This method of eliminating the potential between two solutions fell into disrepute when it was realized that the excess of the indifferent electrolyte has a marked effect on the activities of the substances involved in the cell reaction. It has been revived, however, in recent years in a modified form a series of cells are set up, each containing the indifferent electrolyte at a different concentration, and the resulting e.m.p. s are extrapolated to zero concentration of the added substance. 

The most general and safe procedure to obtain a point of zero charge is by considering the salt effect on common intersection point (c.l.p.) is found at different indifferent electrolyte concentrations, the pAg or pH, of the c.l.p. is identified as pAg or pH°. reasoning that when there is no double layer, there Is no charge to be screened and hence no Influence of added indifferent electrolyte. In principle this procedure is correct the main problem is to ensure that the electrolyte is really indifferent, that is, it contains only generlcally adsorbing Ions. 

Equations (2)-(4) show that the total potential energy of interaction between two colloidal spherical particles depends on the surface potential of the particles, the effective Hamaker constant, and the ionic strength of the suspending medium. It is known that the addition of an indifferent electrolyte can cause a colloid to undergo aggregation. Furthermore, for a particular salt, a fairly sharply defined concentration, called critical aggregation concentration (CAC), is needed to induce aggregation. 

The screening effect of the indifferent electrolyte is shown in panel (a). For high salt concentration (2M) the electrostatic interaction is small and the (1 — h) vs. pH curve resembles the (1 — h) vs. pH. curve shown in Fig. 2a. The lower the salt concentration, the larger become the deviations from the (1 — 0h) vs. pH curve. The effect of Ci on the charging behaviour is illustrated in panel (b). The curve for Ci = oo corresponds with the curve at O.IM salt in panel (a). For low Stern layer capacitances the screening of the surface charge by electrolyte is very poor and charging the surface becomes extremely difficult. Panel (c) shows a plot of vs. pH at the same salt concentrations as shown in panel (a). 

The overall proton adsorption from an indifferent electrolyte solution on a heterogeneous surface can simply be described as the sum of the local adsorption contributions. The effect of lateral interactions should be taken into account in the local isotherm. For a patchwise surface with a discrete distribution of intrinsic affinity constants the total... 

Ardizzone, S., The oxide/solution interface Specific effects of indifferent electrolytes, J. Electroanal. Chem., 239, 419, 1988. 

In contrast, with ionic surfactants the adsorption process is relatively more complicated as the repulsion between the head groups and the effect of presence of any indifferent electrolyte must be considered. Moreover, the Gibbs adsorption equation must be solved, taking into account the surfactant ions, the counterion and any indifferent electrolyte ions present. For a strong surfactant electrolyte such as Na+ R ... 

In this adsorption experiment, the pH was controlled at 5.3, so that the dominant form of the organics in solution was R" rather than RH. The adsorption isotherm becomes, in effect, a plot of Sr (amount of organic adsorbed) versus (R ), the solution activity of dissociated organic acid, because (Rt) (R") at pH 5.3. Since (H ) < K , the last term in equation 10.62 is approximately equal to (Rt). In this particular experiment, the bathing indifferent electrolyte was 0.05 M NaC104, so that (X ) can be assumed to be constant along with (H" ). Equation 10.62 then takes on a simplified form for the adsorption isotherm of the benzoic acids on any particular variable-charge mineral ... 

It can be seen that the effect of indifferent electrolytes on the zeta-potential of the mineral particle depends not only on its concentration but also on the valency of the counterions involved. The Schultz-Hardy rule expresses the dependence of the ability of a coagulant on the valency of the ions as follows ... 

Indifferent Electrolyte An electrolyte whose ions have no significant effect on the electric potential of a surface or interface, as opposed to potential-determining ions, which have a direct influence on surface charge. This distinction is most valid for low electrolyte concentrations. Example For the Agl surface in water, NaN03 would be an indifferent electrolyte, and both Ag+ and I" would be potential-determining ions. 

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