The Mean Salt Method

The mean salt method derives implicitly from the concept of ionic strength, as expressed by Lewis and Randall (1921). It is assumed that, within the range of the ionic strength of interest, for a standard uni-univalent electrolyte such as KCl, the following assumption is valid  

From equation 8.34, with a reasonable approximation (see eq. 8.29), we can derive 

Because the values for the various salts in solution may be experimentally obtained with a satisfactory precision, equation 8.35 is used to derive the corresponding values of individual ionic activity coefficients from them. For instance, from a generic univalent chloride MCI, the y of which is known, we may derive the 7+ of M+ by applying 

Similarly, the same method and the same mean salt furnish values of individual ionic activity coefficients for other ions—e.g., the sulfate group SO  

For a salt with both cation and anion different from those of the mean salt (e.g., CUSO4), double substitution is required—i.e., 

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Example 3.1 Determination of single-ion activity coefficients for Ca from mean values for CaCl2 using the mean-salt method. 

In the mean-salt method, the behavior of KCl in solution is the standard basis for obtaining individual ion activity coefficients. Various lines of evidence indicate that /k+ and fc - have similar values that is, as an approximation,... 

Single-ion activity coefficients at higher ionic strength are estimated by using an empirical approach in which complex ion and dipole interactions are accounted for by direct laboratory measurements. One such experimentally based approach that can be applied to seawater is the mean salt method (MSM). This procedure is based upon measurements... 

This assumption seemed reasonable in view of the similarity of the sizes and limiting conductances of the two ions. It gave rise to the Macinnes convention, which enables the activity coefficients of other ionic species to be evaluated from the known mean activity coefficients of selected electrolytes. This process, called the mean salt method", has been used extensively and with apparent success in studies of the seawater medium. Carrels and Thompson (40,41) used a glass electrode reversible to Na" to establish a reference point for the activity coefficient of that ion in seawater. The Macinnes convention was then applied to obtain data for the other ions present. The procedure proposed by Maronny and Valensi (42,43) for the determination of standard pH values utilizes Equation 6, where is... 

Another arylation method, in the case of nitrogen heterocycles, does not need a halogenated derivative but a heterocycle activated by triflic anhydride260,261 (reaction 22). Simple aryl halides usually do not react with phosphines and special methods therefore have to be used for their arylation. The most widely used is the complex salt method , in which an aryl halide is heated with a phosphine in the presence of a transition metal such as nickel (II)2e (reaction 23). The catalytic cycle probably takes place by means of a reduced nickel(I) complex, generated in situ from the starting nickel(II) salt this nickel(I) species could undergo an oxidative addition of the aryl halide to yield a transient nickel(III) adduct, which after the reductive elimination of the aryphosphonium affords the recovery of the first active-nickel(I) complex (reaction 24). 

Sulfur mustard reacts rapidly with chlorine or with bleach, and this reaction is a suitable means of decontamination. Nitrogen mustards, however, chlorinate extremely slowly thus chlorination is not suitable for their decontamination. The formation of water-soluble salts, such as by neutralization with sodium bisulfate, is the usual method for nitrogen mustard removal from contaminated surfaces. The mustard salts are much less vesicant than the corresponding free bases. 

If the one-point calibration in ambient air is not sufficient, the next best approach is to use the calibration box method.- The air state is created in a closed box made of nonhygroscopic material, like metal or plastic. A controlled state of humidity is maintained by exposing the air in the box to a liquid surface of a saturated salt solution. In practice, a dish containing the saturated water solution of a salt is placed on supports at the bottom of the box. The air in the box is circulated by means of a small fan. The box should be airtight and positioned in a constant temperature environment. The calibrated instruments are placed in the box. A dewpoint hygrometer can be used as a reference. A wide range of humidity can be created by using solutions of different salts. Table 12.5 shows a few examples of equilibrium humidities achieved with different salt solutions. 

Poloxamers are used primarily in aqueous solution and may be quantified in the aqueous phase by the use of compleximetric methods. However, a major limitation is that these techniques are essentially only capable of quantifying alkylene oxide groups and are by no means selective for poloxamers. The basis of these methods is the formation of a complex between a metal ion and the oxygen atoms that form the ether linkages. Reaction of this complex with an anion leads to the formation of a salt that, after precipitation or extraction, may be used for quantitation. A method reported to be rapid, simple, and consistently reproducible [18] involves a two-phase titration, which eliminates interferences from anionic surfactants. The poloxamer is complexed with potassium ions in an alkaline aqueous solution and extracted into dichloromethane as an ion pair with the titrant, tet-rakis (4-fluorophenyl) borate. The end point is defined by a color change resulting from the complexation of the indicator, Victoria Blue B, with excess titrant. The Wickbold [19] method, widely used to determine nonionic surfactants, has been applied to poloxamer type surfactants 120]. Essentially the method involves the formation in the presence of barium ions of a complex be-... 

There is difficulty in defining the absolute mobilities of the constituent ions in a molten salt, since it does not contain fixed particles that could serve as a coordinate reference. Experimental means for measuring external transport numbers or external mobilities are scarce, although the zone electromigration method (layer method) and the improved Hittorf method may be used. In addition, external mobilities in molten salts cannot be easily calculated, even from molecular dynamics simulation. 

Hassan et al. [39] used a sensitive color reaction method for the determination of primaquine in pharmaceutical preparation. Primaquine was treated with diazo-p-nitroaniline in acidic medium to give an orange-yellow product with an absorbance maximum at 478 nm. When the medium was made alkaline, bathochromic, and hypochromic shifts occurred the new maximum was located at 525 nm. The mean percentage recoveries for authentic samples amounted to 100 and 100.21 by the acid and alkaline procedures, respectively (P = 0.05). Both reactions could be used to determine primaquine salts in pharmaceutical preparations. The results obtained were in good agreement with those of the official methods. Recoveries were quantitative by both methods. 

The nucleophilic displacement of suitable para substituents in analogues of malachite green is used as a means of synthesis of some important acid dyes. For example, Cl Acid Blue 83 (6.176 R = H) is made by the aldehyde method, using 4-chlorobenzaldehyde and N-ethyl-N-(3-sulphobenzyl)aniline. The resulting leuco base is oxidised to the colour salt,... 

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