Cadmium complexes equilibrium constant

Cadmium, tris[4,4,4-trinuoro-l-(2-furyl)-l,3-butanedione]-structure, 65 Cadmium complexes equilibrium constant solvent effect, 516 Cage compounds in gravimetry, 525 Cage mechanism photochemistry, 393 Cages, 135 formation... 

Fig. 2.2 shows the adsorption spectra of a colloidal CdS solution prepared by the above method in the presence of cadmium complexones of various nature. The position of the colloids adsorption band indicates that the equilibrium size of the colloidal particles decreases as the stability constant of the complex increases. This may relate to the fact that it is precisely the decay rate of the cadmium complex that determines the number of nuclei N and, hence, the size of the forming particles. This is supported by the fact that with the fixed initial (before the addition of the sulfide anion and after the addition of the ligand) concentration of activated Cd2+ (lg[CdL]/[Cd2+]) = const and [Cd°] = const), for complexones of various nature, the sizes of colloidal particles differ the stronger the initial complex, the smaller the particle size. 

The uncertainty for the cadmium complex has been increased considerably by the review due to the uncertainty in the value of the equilibrium constant. Aruga concurrently determined the corresponding quantities for the sulphate complexes and calculated theoretically the difference between the enthalpy change at / = 0 and 0.5 M to be 4.05 kJ-mol. The correction was estimated by the review to be (4.40 0.20) kJ-mol. A comparison of the sulphate data extrapolated to standard conditions with other calorimetric data in [73POW] indicates that the results reported by Aruga are low by about... 

Using the equilibrium constants below, calculate the concentrations of free (uncomplexed) cadmium ion in a freshwater with a chloride concentration of 15mg/L, and in seawater containing 17000mg/L chloride. Ignore complexation with other ions. 

An interesting example of the application of SEC is the separation of free Cd (II) and the complex with fulvic acid (FA), which is the soil organic acid considered to be responsible for metal ion transport in the environment. Cadmium is of increasing concern as a heavy metal environmental pollutant and the understanding of cadmium transport requires knowledge of the equilibrium constant for... 

This atom-by-atom growth mechanism fits experimental results very well for CdS deposition from QCM investigations in ammonia-thiourea solutions, as shown in figure 13. The rate constants take into account the equilibrium composition of the bath with respect to the concentration of the various cadmium complexes with hydroxide ions and ammonia (see section 3). 

It was shown [23] that addition of ligands that form complexes with Cd influences essentially the size of the CdS nanocolloids. Namely, an increase in the stability of a cadmium complex precursor reduces the equilibrium size of the colloidal particles. The EDTA anions appear to be an exception to this rule because they form strongly chelated Cd complexes with a stability constant of 5 x lO [24] the presence of this ligand dissolves CdS particles of a size less than a certain diameter of the CdS particles in a homogeneous colloidal solution. Data on the CdS synthesis in the inner cavities of the lipid vesicles are in a good agreement with the results of the cited work. 

The incorrect nature of this concept has been convincingly demonstrated by the equilibrium studies of Ahrland [Ah 76] in aqueous and in dimethyl sulphoxide solutions. In order to illustrate the effect of the solvation of the anions on the stabilities of their metal complexes, Ahrland compared the stepwise stability constants, determined potentiometrically in water and in dimethyl sulphoxide, of the zinc and cadmium complexes of halide ions, which form hydrogen bonds with strengths decreasing in the sequence Cl >Br >I . As can be seen from the data relating to the cadmium complexes in Table 6.1, the absolute values of the equilibrium constants in dimethyl sulphoxide solution were considerably higher than those in water. In addition, the-stability sequences for the various halide... 

In principle, the shifts of the individual species in rapid equilibrium may be extracted by the application of known equilibrium constants to the results from solutions covering a range of compositions. This has been done for zinc and cadmium halide systems. Such treatments assume that the shift of an individual species is independent of the concentrations of the other species present. However, results for the nonlabile complexes of group VIII metals suggest that there will be some dependency but it is difficult to estimate the possible magnitude for metals such as cadmium. The accuracy of a determined chemical shift is poor if the species does not have a large concentration in at least one solution measured. Finally, considerable errors may be involved if the NMR measurements are made under different conditions (e.g., higher concentration) from those for which the equilibrium constants were evaluated. 

If ammonium hydroxide (ammonia in water)—a common complexant for Cd in CD—is added to a suspension of Cd(OH)2, the Cd(OH)2 will redissolve, assuming enough ammonia has been added. How much is enough ammonia This can be calculated from the stability constant of the complex between ammonia and Cd. The equilibrium of this reaction to form the cadmium tetraamine complex is given by... 

Much work has been devoted to the halide complexation of these elements in non-aqueous media. Equilibrium and calorimetric measurements for the formation of the [MX ](n-2) (M = Zn or Cd X = Cl, Br, I or SCN n = 1-4) anions in dimethyl sulfoxide (DMSO) have shown that stability constants follow the same order, but are much larger than those found for aqueous solution zinc exhibits an enhanced hardness as an acceptor in DMSO as compared to cadmium. Calorimetric measurements indicate a change from octahedral to tetrahedral coordination with increasing halide concentrations.1002-1006... 

Specifying a reasonable N value and substituting in Eq. (3) the value a = 1.09 0.24 J/m2 estimated from the data of [4], one may determine by Eq. (3) the equilibrium size of the colloidal particle, which appears to be dependent on the stability constant of the complex. A detailed analysis of this calculation is reported elsewhere [2]. The a value was estimated as follows. According to the data of [4], the range of solubility product (SPcas) values was found from the condition of dissolving the cadmium sulfide particles of size 2R = 25 A by the added Na2EDTA and concurrent stability of these particles to alkalization ... 

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