Ammine complexes stability constants

Table 8-4. Stability constant data for copper(ii) and nickel(ii) ammine complexes.

The participation of Cd(OH)2 in the deposition of CdS (and other metal chalcogenides) has been demonstrated or suggested on many occasions. Kitaev et al. presented a theoretical thermodynamic treatment of the Cd " /ammonia/ thiourea system to show when Cd(OH)2 should be present as a solid phase in the deposition solution [36]. A graphical representation of this analysis is shown in Eigure 3.1. This graph is based on two equilibria the solubility product of Cd(OH)2 and the stability constant of the ammonia (ammine) complex of Cd. Consider first the former ... 

Reference 85 presents the thermodynamic side of the previous paper. It is pointed out that although both ammonia and thiourea are present in the solution, because of the much higher stability constant of the Ag-thiourea complexes compared to the Ag-ammines, essentially all the Ag will be present as a thiourea complex. In this case, it can be assumed that the role of ammonia is only to control pH. 

Aluminum hydroxy species, 65,69,160 Stability constants, 69 Stability diagrams, 78 pH of minimum solubility, 65, 71, 72 Ammonium, 326, 331 Volatilization, 330 Oxidation, 334-336,472 Nitrate, 334-336,472 Adsorption, 336,465-466 Metal-ammine complexes, 460—461, 465... 

Additional alterations in the work terms with the electrode material for outer-sphere reactions may arise from discreteness-of-charge effects or from differences in the nature of the reactant-solvent interactions in the bulk solution and at the reaction plane. Thus metals that strongly chemisorb inner-layer solvent (e.g., HjO at Pt) also may alter the solvent structure in the vicinity of the outer plane, thereby influencing k bs variations in the stability of the outer-sphere precursor (and successor) states. Such an effect has been invoked to explain the substantial decreases (up to ca. 10 -fold) in the rate constants for some transition-metal aquo couples seen when changing the electrode materiaf from Hg to more hydrophilic metals such as Pt. Much milder substrate effects are observed for the electroreduction of more weakly solvated ammine complexes . 

It is observed in the experiment that the iron nail immediately creates a copper deposit in a blue colored copper sulfate solution (see E8.1), whereby this does not happen in the violet colored ammine complex solution. A trace of copper deposit can only be observed after it has been dipped into the complex solution for a while (see E9.6). It is possible to verify this hypothesis with the help of a second reaction, the metal hydroxide precipitation (see E9.6) a greenish blue deposit is commonly observed in the blue solution of hexaaquacopper ions, but not in the solution of tetraamminecopper ions. Apparently, copper ions and water molecules are not very tightly bonded in aqua complexes, but copper ions and ammonia molecules in ammine complexes are there is a weak stability of aquacopper ions, but a great stability of tetraamminecopper complexes. The stability constants can be taken and interpreted if one wants a quantitative explanation of these phenomena. 

In these conditions, the calculation of aM is immediate since the stability constants intervening in its expression are known. (Let s recall incidentally that the strategy consisting of adding a great excess of reagent to simplify calculations is a method frequently used in analytical chemistry. The closer we are located to the equivalence point, the better the condition [NH3] Cnh3 is since, by the definition of a satisfactory titration, the cation and ammine complexes concentrations must be very weak at diis point.)... 

We must note that this expression is legitimate only if the ammine complexes concentrations are negligible in the mass balance relation on the buffer.) Developing the stability constants expressions as a function of the concentration of magnesium... 

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