Chloro complexes solubility

To understand why AgCl shows a more complex solubility relationship than that suggested by equation 8.2, we must recognize that Ag+ also forms a series of soluble chloro-complexes... 

Equation 8.7 explains the solubility curve for AgCl shown in Figure 8.1. As Ch is added to a solution of Ag+, the solubility of AgCl initially decreases because of reaction 8.1. Note that under these conditions, the final three terms in equation 8.7 are small, and that equation 8.1 is sufficient to describe the solubility of AgCl. Increasing the concentration of chloride, however, leads to an increase in the solubility of AgCl due to the soluble chloro-complexes formed in reactions 8.3-8.5. ... 

Several processes are available for the recovery of platinum and palladium from spent automotive or petroleum industry catalysts. These include the following. (/) Selective dissolution of the PGM from the ceramic support in aqua regia. Soluble chloro complexes of Pt, Pd, and Rh are formed, and reduction of these gives cmde PGM for further refining. (2) Dissolution of the catalyst support in sulfuric acid, in which platinum is insoluble. This... 

The solubility of AS2O3 in water, and the species present in solution, depend markedly on pH. In pure water at 25°C the solubility is 2.16 g per lOOg this diminishes in dilute HCl to a minimum of 1.56g per lOOg at about 3 m HCl and then increases, presumably due to the formation of chloro-complexes. In neutral or acid solutions the main species is probably pyramidal As(OH)3, arsenious acid , though this compound has never been isolated either from solution or otherwise (cf. carbonic acid, p. 310). The solubility is much greater in basic solutions and spectroscopic evidence points to... 

In the thermal production of gold coatings on ceramics and glass, paints are used which comprise Au chloro-complexes and sulfur-containing resins dissolved in an organic solvent. It seems likely that polymeric species are responsible for rendering the gold soluble. 

This mechanism can explain the formation of Te-bearing Au-Ag veins in which sulfides are poor in amounts. The deposition of sulfides is generally difficult by this mechanism because solubilities of sulfides generally increase with decreasing of pH. However, if temperature of mixed fluid decreases considerably by this mechanism, the deposition of sulfides may be possible, because solubilities of sulfides due to chloro complexes decrease with decreasing of temperature. 

In its chemistry, cadmium exhibits exclusively the oxidation state 4- 2 in both ionic and covalent compounds. The hydroxide is soluble in acids to give cadmium(II) salts, and slightly soluble in concentrated alkali where hydroxocadmiates are probably formed it is therefore slightly amphoteric. It is also soluble in ammonia to give ammines, for example [Cd(NH3)4]2+. Of the halides, cadmium-(II) chloride is soluble in water, but besides [Cd(H20)J2+ ions, complex species [CdCl]+, [CdCl3] and the undissociated chloride [CdCl2] exist in the solution, and addition of chloride ion increases the concentrations of these chloro-complexes at the expense of Cd2+(aq) ions. 

An even more serious problem can arise when dissolved species expected to predominate at high temperatures are undetectable at 25°C or are only present at concentrations which are too low for them to be adequately characterized thermodynamically. Examples are certain transition metal chloro-complexes (9,10) and mixed complexes of such metals with hydroxide and another ligand (11,12). Thus it seems that chloride complexing so alters the aqueous chemistry of copper and gold that supposedly inert gold components in autoclaves are reversibly oxidized by Cull (10) and it is likely that mixed oxine and hydroxy complexes of Fell contribute considerably to the gross under-estimation (by a factor of up to 10 ) of magnetite solubility in oxine (12,14). 

Noble metals, such as gold, platinum, palladium, rhodium and iridium are not attacked by nitric acid at ordinary temperatures. These metals, however, dissolve in aqua regia (3 1 HCl— HNOs mixture). Nitric acid in aqua regia oxidizes gold to Au , which readily combines with Cl to form soluble chloro-complex, AuClF. 

The chloride salt of the solid complex has recently been shown to have a chloride bridge.18 In solution, the yu-amido-yu-chloro and /z-amido-aquo-chloro complexes appear to equilibrate rapidly (see Eq. c, p. 209). It is possible that the yu-amido-yu-chloro complex is never present in solution in large amounts but that it is much the least soluble form. The aquo-chloro complex also equilibrates with the /z-amido-yu-hydroxo complex in aqueous solution ... 

The unexpectedly high solubility of K2[TcBr6] (in contrast to that of the fluoro and chloro complexes) in methanol appears to be due to partial substitution of Br by MeO . By the use of KOR, salts such as K2[Tc(OMe)6] and K2[Tc(0CH2CH20)3] may be isolated. These complexes show a f(TcO) IR absorption at 450-460 cm-1 (356). A crystal structure of 28, with the zwitterionic tripod ligand Me3N+C(CH20 )3, shows octahedral geometry with Tc-0 distances of 1.987(4)-2.005(4) A. Complex 28 is water soluble and stable at pH > 4 for over 24 hr (357). 

Because mercury forms relatively stable hydroxo, sulfato, and chloro complexes in solution, the solubilities and relative stabilities of mercury minerals depend heavily on ambient solution compositions. Figure 4 illustrates the calculated effect of pH and total sulfate on the solubility of schuetteite. The curves take into account all complexes for which data are available in Martell and Smith (18) and precipitation of HgO they cross when changes in solution composition result in changes in dominance among complexes. Schuetteite is quite soluble relative to HgS and elemental mercury under common conditions. 

Figure 7-2 represents data for solubility of silver chloride plotted to illustrate the minimum solubility, the common ion effect and intrinsic solubility S°, and the formation of the chloro complex. As Figure 7-25 indicates, at low concentrations of excess chloride an essentially linear relation is obtained between solubility and the reciprocal of the product of chloride ion concentration and the square of the activity coefficient. The zero intercept corresponds to S° (in this case an intrinsic solubility... 

The solubility of PbS and ZnS in waters containing dissolved chloride is enhanced by the formation of metal-chloro complexes MeCl, MeCl , MeClJ, and MeCl4. Most fluids that have concentrations of dissolved lead and dissolved zinc exceeding 1 mg also have chlor-... 

Fig. 5.5-1 The logarithmic concentration diagram for the chloro complexes of Ag(I) in an aqueous solution equilibrated with solid AgCl. The colored line shows the silver solubility SAg. Note that, in this case, the solubility of the insoluble neutral species, AgCl, is quite substantial between a pCl of 2 and 3 it is the dominant component of the silver solubility SAg.

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