Constants for Some Complex Ions

Table 18.2 Formation Constants for Some Complex Ions ...

Table 56 Formation Constants for some Complexes of Silver(I) Ions with Complexones...

The value of for Ag(NH3)2 is 1.7 X 10. Its large value means that the complex ion is quite stable. When a large amount of NH3 is added to a solution of Ag, you expect most of the Ag ion to react to form the complex ion. Table 18.2 on the following page lists values for the formation constants of some complex ions. 

The sorption selectivity for more complex ions (e.g., ions of antibiotics) in competition with small ions increases to a still greater extent [59]. Particularly high constants for selective bonding (up to some hundreds and thousand) have... 

The kinetic inertness of [Fe(CN)6]4 is typified by the extremely slow thermal displacement of CN by a,a -diimines. Such reactions are however catalyzed270 by a variety of metal ions such as Hg2+ and the stability constants for some of the intermediate heteropolynuclear complexes have been determined.271... 

The most typical route for metal ion removal/ recovery from polluted aqueous media is precipitation (see Section 10.2). However, in some cases the target metal ion cannot be precipitated in a pure form because other metal ions may co-precipitate. Selective complexation can then be used to promote the solubilization of either the target ions or the accompanying ions. Here, the constant for metal complexation must be greater than the solubility product. (Note that in order for this comparison to be valid, one has to be aware of the differences in the units of the constants). For example, one can recover Ag... 

Evidently it is more important to determine the cupric ion concentration than the total copper concentration in natural waters. Polarographic methods have been used to measure the ligand concentration (complexing capacity) (10) and to determine stability constants for some strong chelators (11). 

TABLE 1.5 Acid Hydrolysis Constants (pAas) for Some Aquo Ions and Complex Metal Ions at 25 °C (Selected from Basolo and Pearson,22 and pH Precipitation Ranges of Hydroxides or Hydrous Oxides (Adapted from Walton23)... 

The more effectively a ligand competes with H2O for a coordination site on the metal ions, the smaller is. This tells us that in a comparison of complexes with the same number of ligands, the smaller the value, the more stable the complex ion. Some complex ions and their dissociation constants, K, are listed in Appendix I. 

Fig. 5. Second order rate constants for the complex formation of the trivalent lanthanide ions and some d i-ions of transition metals with murexide as a function of reciprocal ionic radius (values from ref. 10)...

It is usually the case that, when the speciation of Al in soil solutions is investigated, a large fraction of the soluble Al is found to be in the form of organic and fluoride complexes. Some of the Al may also be complexed with soluble silicate, although stability constants for such aluminosilicate ions are not known. There is... 

The method of frontal analysis on an ion-exchange column was used to study the formation of weak chloro complexes of nickel(II), cobalt(II) and copper(II). Although, the reported dissociation constant for the complex NiCr (X iss = (4.6 0.1), which can be converted to log,) X, = - (0.66 0.01)) is close to other reported values, some experimental data, such as the temperature of the measurements, were not published. Therefore, the reported constant is rejected in this review. 

In keeping with the hard or class a nature of the Fe " ion the most stable complexes are formed with the small non-polarizable F ion. Consecutive formation constants for some fluoro and chloro complexes in aqueous solution may be found in ref. 322. Bromo complexes are even less stable than chloro complexes while with the easily oxidizable 1 ion no stable simple iodides have been prepared although a very few complexes containing Fe "—I bonds are known in combination with other ligands. Consistent with the stability order F > CL > Br is the occurrence of higher coordination number Fe complexes with F than with Br . Thus, while F readily forms hexacoordinate [FeFfi] complex ions and no tetrafluoro complex ions, CL forms both [FeClgf and [FeCl4] while Br apparently does not form a stable hexabromo complex [FeBr ] ". 

A comparison of the formation constants for metal-fulvic acid complexes shown in Table 5-13 with those values for the complexes of the same metals with NTA (Table 5-10) would seem to indicate that the metal-fulvic acid complexes are much weaker than the metal-NTA complexes. Indeed some of the values of the constants for metal-fulvic acid complexes approach the values for the very weak inorganic ion pairs (e.g., MgCOs , log = 2.9 CaS04 logff = 3.4). Morgan has pointed out that the values for the metal-fulvic acid complexes were measured at much lower pH values than the K values for other complexing agents such as NTA and EDTA. The stability constants for NTA complexes reported in Table 5-10 are for the totally deprotonated species,... 

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