Molar salt concentration

Molar salt concentration within a polyelectrolyte and in the surrounding medium, respectively (Chap. XIII). 

This equation tells us that, since is proportional to the molar salt concentration (see, for example, [3.5.7]), the electrostatic persistence length (or chain stiffness) decreases Inversely proportionally with Increasing salt concentration. In fig. 5.5 we present, as an experimental example, the salt dependence of for DNA, as measured by several techniques. For comparison, the theoretical dependence based on [5.2.24] is also shown. 

In practice, a set of curves developed by Kemper and Quirk (Fig. 8.10), yields approximate electric potentials as a function of distance from the colloid surface. Such potentials can then be substituted directly into the Boltzmann equation to infer cation and anion distributions. 7/, is the scaled electric potential (equal to —Zef/fkT of Eq. 8,15) at the midplane between interacting colloids, T is the surface charge density in coulombs m-2 (96.5 times the ratio of CEC, in mmoles charge kg-1, divided by the specific surface, in m2 kg-1), Z is the valence of the exchangeable cation, Co is the molar salt concentration in the bulk solution, and x is the distance (in nm) from the midplane between colloids to the plane at which the ion concentration is to be calculated. 

Molar salt concentration for all salts except RbCl. The dissolution rate in the TMAH with the added salts, however, fell monotonically from values around 35 nm/sec without added salt to approximately 5 nm/sec with the 1.3 M concentration. Thus, there seemed to be a trade off between a reasonable dissolution rate and a smooth surface. 

Tg value without salt and c = molar salt concentration. This result was interpreted as the effect of ionic crosslinks. 

Conductivity measurements yield molar conductivities A (Scm2 mol-1) at salt concentration c (mol L-1). A set of data pairs (Af, c,), is evaluated with the help of non linear fits of equations [89,93,94] consisting of the conductivity equation, Eq. (7), the expression for the association constant, Eq. (3), and an equation for the activity coefficient of the free ions in the solution, Eq.(8) the activity coefficient of the ion pair is neglected at low concentrations. 

Figure 5. (a) The ( A, SO,) anion symmetric streching mode of polypropylene glycol)- LiCF,SO, for 0 M ratios of 2000 1 and 6 1. Solid symbols represent experimental data after subtraction of the spectrum corre-ponding to the pure polymer. Solid curves represent a three-component fit. Broken curves represent the individual fitted components, (b) Relative Raman intensities of the fitted profiles for the ( Aj, SO,) anion mode for this system, plotted against square root of the salt concentration, solvated ions ion pairs , triple ions, (c) The molar conductivity of the same system at 293 K. Adapted from A. Ferry, P. Jacobsson, L. M. Torell, Electrnchim. Acta 1995, 40, 2369 and F. M. Gray, Solid State Ionics 1990, 40/41, 637. 

At salt concentration below those shown in Fig. 5, molar conductivity behavior has been identified with the formation of electrically neutral ion pairs [8]. Between concentration of 0.01 and 0.1 mol L 1 (up to an 0 M ratio of -50 1) the molar conductivity rises and this can be explained by the formation of mobile... 

Poly(dG-dC) poly(dG-dC) and its methylated analogue structures assume left-handed conformation (Z-DNA) in high molar sodium salt (Na", K" ), in low molar divalent cations (Ca", Mg", Ni ), micromolar concentrations of hexaamine cobalt chloride (Co(NH3)6)Cl3 and in millimolar concentrations of polyamines. In order to analyse the binding of berberine to Z-form DNA, Kumar et al. [186] reported that the Z-DNA structure of poly(dG-dC) poly(dG-dC) prepared in either a high salt concentration (4.0 M) or in 40 mM (Co(NH3)6)Cl3 remained invariant in the presence of berberine up to a nucleotide phosphate/alkaloid molar ratio of 0.8 and suggested that berberine neither bormd to Z-form DNA nor converted the Z-DNA to the... 

A borehole stability model has been developed that takes into account both the mechanical and the chemical aspects of interactions between drilling fluid and shale [1231]. Chemically induced stress alteration based on the thermodynamics of differences in water molar free energies of the drilling fluid and shale is combined with mechanically induced stress. Based on this model, it should be possible to obtain the optimal mud weight and salt concentration for drilling fluids. 

Salt activation falls into two classes with respect to the valency of the cation component. With divalent cations and at pH 6, maximum activation is produced at about 0.03 M concentration. At higher concentrations with the same pH, suppression of activity occurs. Monovalent cations in general produce maximum activation at pH 6 in 0.10 M concentration and do. not suppress activity below molarities of 1.0. Maximum activity is obtained at a lower pH and lower concentration of divalent cations than monovalent. The maximum activity obtained at the optimum salt concentration for a given pH value is, within experi-... 

Salt Concentration of salt (molarity) Reaction mixture (pH) Relative activity of amylase... 

As seen from Eq. (130) an activity coefficient may deviate significantly from unity at higher salt concentrations. The activity coefficient can therefore also be used as a measure of the deviation of the salt solution from a thermodynamically ideal solution. If the chemical potential of a solute in a (pressure-dependent) standard state of infinite dilution is /x°, we find the standard partial molar volume from... 

The electrolyte concentration is very important when it comes to discussing mechanisms of ion transport. Molar conductivity-concentration data show conductivity behaviour characteristic of ion association, even at very low salt concentrations (0.01 mol dm ). Vibrational spectra show that by increasing the salt concentration, there is a change in the environment of the ions due to coulomb interactions. In fact, many polymer electrolyte systems are studied at concentrations greatly in excess of 1.0 mol dm (corresponding to ether oxygen to cation ratios of less than 20 1) and charge transport in such systems may have more in common with that of molten salt hydrates or coulomb fluids. However, it is unlikely that any of the models discussed here will offer a unique description of ion transport in a dynamic polymer electrolyte host. Models which have been used or developed to describe ion transport in polymer electrolytes are outlined below. 

By the law of mass action the concentration of these ion pairs will grow at the expense of the free ions, as the overall salt concentration increases. Since the ion pairs carry no charge the conductivity per unit salt concentration, i.e. the molar conductivity, must fall as observed. As the salt concentration is further increased a minimum in A is eventually reached at which the concentration of ion pairs is a maximum. Two mechanisms have been postulated for the increase in ion concentration, and hence A, beyond the minimum. The first mechanism assumes that at... 

The induction time tau for the precipitation process, where t = gC". C is the square root of the molar ion concentration product of the precipitating salt, and g and n are empirical constants. In this respect, n represents... 

Fig. 24. Parallel effects of salts on the molar reduction in the precipitation temperature of polyethylene oxide in the salt concentration of I mol-1-1, ATm and the transition molality of AMsopropylacrylamide gel, CT. In the case of continuous phase change, Cr was defined as the point of inflexion in the volume-molality curve...

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