Dependence on ionic strength

Ascorbic acid is oxidised by hexaeyanoferrate(III) to produce dehydroascorbic acid 

As aqueous solutions of [Fe(CN)g] have a maximum absorption at 418 nm with a molar absorption coefficient 1012 M cm and the other reactants and products are colourless. 

Fignre 3.10 Relative rates as a function of initial concentration of AzocoU. 

Experiment 3.7. Experimental determination of the effect of ionic strength [13] 

Material. Stopwatch, colorimeter or spectrophotometer, 1 cm spectroscopy cuvette, 100 cm volumetric flasks, 25 cm pipettes, 100 cm Erlenmeyer flasks. 

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The lack of dependence on ionic strength in the first reaction indicates that it occurs between neutral species. Mono- or dichloramine react much slower than ammonia because of their lower basicities. The reaction is faster with CI2 because it is a stronger electrophile than with HOCl The degree of chlorination increases with decreasing pH and increasing HOCINH mol ratio. Since chlorination rates exceed hydrolysis rates, initial product distribution is deterrnined by formation kinetics. The chloramines hydrolyze very slowly and only to a slight extent and are an example of CAC. 

No evidence has yet been obtained in support of such a mechanism in the present context, and it is unlikely that it has general applicability. NMR measurements for example provide no support for a conformational change of PCu(I) on association with Cr(III) complexes (13). Moreover it has in one case been demonstrated that ket in (4) is not dependent on ionic strength, consistant with an intramolecular as opposed to intermolecular process (11). Although caution is required, particularly as isolated examples of (7) - (8) may exist, the invoking of such a mechanism seems to be a case of looking for greater complexity than may actually exist. A reasonable stance, and one which we have adopted, is that discussion should proceed in terms of (5) -(6) until evidence in support of (7) - (8) is obtained. 

From Ref. (43) earlier estimates arising from vibrational spectroscopy studies of the anion in Ca(NC>3)2 solutions were logic = —0.8 to —0.9, depending on ionic strength (228). A logic value of -0.9 has been reported for the iodate complex (224,225). 

Dankwerts and McNeil ( 3) have employed the method of Van Krevelen et al. to predict the partial pressure of carbon dioxide over carbonated alkanolamine solutions. The central feature of this model is the use of pseudo-equilibrium constants and their dependence on ionic strength. The ratio of the pseudo-equilibrium constant at a certain ionic strength to that at zero ionic strength has been termed the "ionic characterization factor". However, ionic strength alone is insufficient to determine the ionic characterization factors. As well the ionic characterization factors are sometimes not a simple linear function of ionic strength. 

Based on original data of ref (30) see also refs (10) and (11) where uncertainties in extrapolated values are discussed, and ref (12) where calculated dependence on ionic strength is presented. 

Since the stability of CLAs displays a strong dependence on ionic strength, due to electrostatic interactions associated with the surfactant head groups, pH should also have an influence on CLA half-lives. The effect of continuous phase pH on the stability of CLAs dispersed in deionized water at 25°C was investigated by Lye and Stuckey [65]. Above a pH of 6-7, ti/2 values were essentially constant, but began to decline as the continuous phase became more acidic. At low pH values, the excess hydrogen ion concentration led to protonation of the sulfonate head groups of the SDS molecules located at the outer soapy-shell interface. This would have two... 

This equation contains the activity coefficients 71, 72, and 7. Recall from the Debye-Hiickel treatment of ionic interactions in dilute solutions that the magnitude of these coefficients shows the following dependence on ionic strength fi for a solution of electrolytes ... 

Adsorption of ferricyanide (a contaminant of sites of former gas plants) on goethite decreases with rising pH and is dependent on ionic strength it is fully reversible and is thought to involve both inner and outer sphere complexes. Adsorption of ferrocyanide on goethite involves initial formation of inner sphere complexes followed by precipitation of a Berlin Blue-like phase on the goethite surface (Rennert and Mansfeldt, 2001). 

Equation 8-5 allows for the effect of ionic strength on a chemical equilibrium because the activity coefficients depend on ionic strength. 

Fig. 7. The dependence on ionic strength of the rate coefficients for hydrolysis of protonated f-butyl acetate in aqueous sulphuric acid.

He cautions that the correlation may underestimate the true solubility, since due to ozone decomposition (depending on ionic strength 31 as well as the type of ions (see below) and... 

Starting from the pre-powerstroke state myosin complex with ADP and Pi tightly bound (summarized structure in Table I), the M.D.Pi is in rapid equilibrium with an actin-bound state on the microsecond-millisecond time scale. This is very dependent on ionic strength (Furch et al., 2000 White and Taylor, 1976) and is therefore probably a non-stereo-specific weak binding state and is controlled by the ionic interactions between loop 2 and the N-terminus of actin. Other ionic interactions may also be involved. This loose association between actin and myosin probably does not alter the overall conformation of myosin. 

Reactions involving charged reactants will occur under non-ideal conditions, and will show a dependence on ionic strength (Equations (7.21) and (7.22). This means that it is necessary to be able to work out the ionic strength from the experimental conditions. The following problem gives practice with this. 

If the observed k depends on ionic strength, then so will A S and AH (see Equation (4.41)) and extrapolation to zero ionic strength is therefore essential. 

Reaction involves an ion and a molecule and could show a primary salt effect. The equilibrium constant describing the formation of the ion pairs also depends on ionic strength. 

Source From R. A. Alberty, Arch. Biochem. Biophys. 389, 94 109 (2001). Copyright Academic Press. Note The apparent equilibrium constants for these reactions do not depend on ionic strength because the equilibrium constants for the chemical reference reactions and acid dissociation do not depend on ionic strength. 

In calculations of ionic equilibria, the required activity coefficients depend on ionic strength and, thus, on the equilibrium. As a result, such calculations are usually carried out by the method of successive approximations. Fortunately, convergence to a unique solution is usually achieved very rapidly in these problems. 

By including Born repulsion in the calculation of the interaction energy profile, the primaty minimum is finite and depends on ionic strength. Allowing the primary to be above the secondary minimum one is... 

In one comparison of predicted and observed deposition rates, the predictions were too strongly dependent on ionic strength, while reasonable agreement was obtained in a second comparison. Inaccuracy in the predicted double-layer force, which would be greatly... 

The force between neutral surfaces (with a surface dipole density) depends on the electrolyte concentrations, as shown in Fig. 3b, particularly at large separations. However, at small separations, the interaction appears to be well described by an exponential with a decay length AH. For neutral lipid bilayers, the equilibrium is reached at a distance of about 20 A, at which the attractive van der Waals interaction balances the repulsive hydration and thermal undulation interactions [43], The experiments regarding the forces between neutral lipid bilayers [11] sample the interactions at separations smaller than 20 A, for which the dependence on ionic strength is much weaker. By adding to the total pressure a typical van der Waals disjoining pressure [12] ... 

Equation 3.7 points out that the variation in the electric field strength (-dy/dx) is related to the second power of the inverse of the thickness of the double layer times /, while Equation 3.8 shows that / decays exponentially with respect to distance (jc) from the surface (Fig. 3.23). A plot of ln( // (/0) versus x produces a straight line with slope k, which is the inverse of the double layer thickness. The assumption ij/0 < 25 mV is not applicable to all soil minerals or all soils. Commonly, clay minerals possess more than 25 mV in surface electrical potential, depending on ionic strength. The purpose of the assumption was to demonstrate the generally expected behavior of charged surfaces. 

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