Ammonia formation constants with

C18-0033. Zinc oxalate, Zn(C2 O4), is sparingly soluble in water (Zjp = 1.4 X 10 ). The Zn ion forms a tetrahedral-shaped complex with ammonia. The formation constant for the complex is 4.1 X 10. How many moles of zinc oxalate will dissolve in 1.0Lof0.200M aqueous ammonia ... 

Other types of equilibria can be treated in much the same way as the ones discussed above. For example, there is an equilibrium constant associated with the formation of complex ions. This equilibrium constant is called the formation constant, Kf. Zn(H20)4+ reacts with ammonia to form the Zn(NH3)2+ complex ion according to the following equation ... 

Copper(II) ion readily forms complexes with various ligands. It slowly forms a deep blue solution in aqueous ammonia. Its ammonia complex, Cu(NH3)4 is very stable, the formation constant, K being 5.6xl0ii... 

The stability (or tendency of the donor atoms to bond to the central metal) of a complex is expressed in terms of a formation constant, ( vhere n is the number of ligands attached to the central metal). Formation constants are equilibrium constants, K, written for the formation of a complex from the fi-ee ligands and central metal. Consider the following example of the formation of several Ni" " complexes with ammonia ... 

It should be noted that the larger the formation constant the more stable the complex. Consider the following example of Ni+ complexes with cyanide and ammonia ... 

The reactions of chlorobenzene and benzaldehyde with ammonia over metal Y zeolites have been studied by a pulse technique. For aniline formation from the reaction of chlorobenzene and ammonia, the transition metal forms of Y zeolites show good activity, but alkali and alkaline earth metal forms do not. For CuY, the main products are aniline and benzene. The order of catalytic activity of the metal ions isCu> Ni > Zn> Cr> Co > Cd > Mn > Mg, Ca, Na 0. This order has no relation to the order of electrostatic potential or ionic radius, but is closely related to the order of electronegativity or ammine complex formation constant of metal cations. For benzonitrile formation from benzaldehyde and ammonia, every cation form of Y zeolite shows high activity. 

With this situation in mind, the formation constant (ft) of the first ammonia molecule making the coordination bond with metal cations was taken as the measure of the ease of ammonia adsorption on metals. The values of (ft) were taken from Ringbom s table (H). The plot of the catalytic activity against formation constants of ammine complexes is shown in Figure 2. The correlation is good except for CdY. Again, the metals with lower formation constant (Na+, Ca+, Mg2+) have no activity for chlorobenzene reaction. 

The formation constant Kt for hydrophobic associations often increases with increasing temperature. This is in contrast to the behavior of Kt for many association reactions that involve polar molecules and for which AH0 is often strongly negative (heat is released). An example of the latter is the protonation of ammonia in an aqueous solution (Eq. 2-10). 

Calculate the conditional formation constant for the Zn-EDTA complex at pH 9.0. in a solution 0.100 M with respect to ammonia. Can zinc be titrated quantitatively with EDTA solution at this pH ... 

The complexes of amino acids with copper are formed according to the general reaction shown in Equation 7.14 [47]. The formation constants for the copper-amino acid complexes are generally greater than that for copper ammonia complex [48]. Therefore, it is anticipated that amino acids should be more effective than ammonia in assisting the dissolution of oxidized copper during CMP. 

The variety of reactions which have been described indicate the large number of chemical species which enter in the troposphere and which may have an impact upon the environment. It is necessary to emphasize that all species are in a dynamic equilibrium for the meteorological turbulence so that in some cases redox and acid-base reactions occur with the formation of stable compounds with high formation constants but nevertheless the reagent species are detectable in the atmosphere. A typical example is the evaluation of the atmospheric aerosol where besides the presence of ammonium sulphates, free ammonia and sulphuric acid may coexist. 

The papers cited above include studies of La and Lu " EDTA-type complexes, (308, 309, 311, 312) Cu complexes, (314, 315) Fe " complexes, (310) and Sm " complexes. (316, 317) Kinetic parameters and stability constants have been calculated in many cases. In one study (315) the variation in the relaxation time of [Cu(EDTA)(H20)] was followed on gradual addition of ammonia at pH 9. Values were found to shorten and then remain constant after addition of a ten-fold excess of ammonia. This is due to the formation of [Cu(EDTA)(NH3)2] " with a formation constant of 18-8. 

In Appendix 4, we find that the logarithms of the stepwise formation constants for the four zinc complexes with ammonia are 2.21,2.29, 2.36, and 2.03. Thus,... 

The reaction between Cu2+ and NH3 goes almost to completion as is suggested by large magnitude of the formation constant. Thus the equilibrium concentration of tetraamine complex is approximately 0.10 M (If x mol/L Cu2+ ion still remain uncoordinated, the concentration of the complex will be 0.10 x). With the formation of 0.10 M Cu(NH3)42+, which requires 4 mol NH3 per mol complex, the ammonia concentration becomes 1.00 4(0.10) = 0.60 M (Dissociation of the complex provides 4x mol NH3 per x... 

We see that only complexes with formation constants of the order of 106 M-1 or more will lead to titration curves with a sufficiently steep change in pL near the equivalence point (at CM VM / CL VL = 1) to be useful for volumetric analysis. None of the common monodentate ligands, such as the halide anions (Cl-, Br , I-) or the pseudohalides (CN , SCN-, N3 ), form such strong complexes, nor do the carboxylic acid anions (such as acetate) or ammonia (NH3). However, in section 5.2 we will encounter special ligands, the chelates, that do form sufficiently strong 1 1 complexes. 

Ammonia will also complex with silver ion to form a colorless complex. (The formation of this complex may be used to dissolve silver chloride precipitate remaining in a filter crucible and thereby clean the crucible.) Two ammonia molecules complex with each silver ion in a stepwise fashion, and we can write an equilibrium constant for each step, called the formation constant K/. 

At the molecular level (Figure 19.14), the actual process is stepwise, with ammonia molecules replacing water molecules one at a time to give a series of intermediate species, each with its own formation constant ... 

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