Complex ions and precipitation

The equilibria involving complex ions and precipitates have applications in geology, medicine, and agriculture. In chemistry, you are more likely to meet up with these equilibria in the laboratory when you carry out experiments in qualitative analysis. 

Potcntiomctric Titrations In Chapter 9 we noted that one method for determining the equivalence point of an acid-base titration is to follow the change in pH with a pH electrode. The potentiometric determination of equivalence points is feasible for acid-base, complexation, redox, and precipitation titrations, as well as for titrations in aqueous and nonaqueous solvents. Acid-base, complexation, and precipitation potentiometric titrations are usually monitored with an ion-selective electrode that is selective for the analyte, although an electrode that is selective for the titrant or a reaction product also can be used. A redox electrode, such as a Pt wire, and a reference electrode are used for potentiometric redox titrations. More details about potentiometric titrations are found in Chapter 9. 

Adsorption and Precipitation vs heterogeneous Nucleation and Surface Precipitation. There is not only a continuum between surface complexation (adsorption) and precipitation, but there is also obiously a continuum from heterogeneous nucleation to surface precipitation. The two models are two limiting cases for the initiation of precipitation. In the heterogeneous nucleation model, the interface is fixed and no mixing of ions occurs across the interface. As a consequence precipi-... 

The fate of heavy metals in aquatic systems depends on partitioning between soluble and partieulate solid phases. Adsorption, precipitation, coprecipitation, and complexation are processes that affect partitioning. These same processes, which are influenced by pH, redox potential, the ionic strength of the water, the concentration of complexing ions, and the metal concentration and type, affect the adsorption of heavy metals to soil (Richter and Theis 1980). 

Moreover, the adsorbability of an ion is generally greater the greater the valency. Matsuno 9 used the precipitating values of cobalt-ammines to determine the valency of the complex ions, employing the equation, deduced from Freundlich s adsorption hypothesis, Sif = S/1V4, where Sy is the equivalent concentration of an A-valent ion, N being the valency of the complex ion, and S the precipitating value of a univalent ion. The results confirmed those obtained by spectroscopic and conductivity methods. 

Reactions of dissolved species with particulate and colloidal suspended matter include adsorption/desorption, complexation, ion-exchange, precipitation/dissolution, coprecipitation during coagulation and flocculation (Morgan, 1966 Stumm and Morgan, 1981 Parks, 1975). These processes are particularly important at the land-sea boundary in estuaries (Duinker, 1980 Martin et al., this volume). The interaction with particles > 0.45 ym is not discussed here. 

As can be seen from the discussions above, the sizes of the nano Titania products are affected most significantly by the pH of the reaction mixture. On the other hand, from the point of view of chemistry, the shift of titanium from the form of ion to complex-ion to precipitate is related closely to the pH. In order to examine the possibility of controlling the size of the product by NH3- neutralization operation and to obtain some information for understanding the reaction mechanism, the influence of the neutralization rate on the mean size and the regularity of pH variation during neutralization are studied experimentally. 

The present work reports the circular dichroism specua and the unpolarized light absorption of the tris-2,2 -dipyridyl and the tris-1,10-phenanthroline complexes of Ni(II), Fe(II), Ru(II), Os(II), Ru(III) and Os(III), The particular enantiomers studied were those forming the less soluble (-)-Co(ox)p salt and the less soluble antimonyl-(+)-tartrate On solubility grounds these enantiomers are expected to have the same absolute configuration as (+)-Co(en , since the latter complex ion preferentially precipitates the (-)-isomer from a solution of racemic K Co(ox). ... 

The anodic partial reaction also involves a charge transfer at the interface because a metal atom loses electrons. It then dissolves in the solution as a hydrated or complexed ion and diffuses towards the bulk. In the vicinity of the metal surface, the concentration generated by dissolution therefore often exceeds that of the bulk electrolyte. Once the solubility threshold is reached, solid reaction products begin to precipitate and form a porous film. Alternatively, under certain conditions, metal ions do not dissolve at all but form a thin compact oxide layer, called passive film. The properties of the passive film then determine the rate of corrosion of the underlying metal (Chapter 6). 

Equilibria Involving Compbx Ions 643 Formation of Complex Ions 643 Complex Ions and Solubility of Precipitates 645 CHAPTER REVIEW GUIDE 646 PROBLEMS 648... 

Gadd, 2009). Biosorption of metal ions is not based on only one mechanism. It is a complicated process and follows complex mechanisms, mainly ion exchange, adsorption by physical forces (e.g., electrostatic), complexation/coordination and precipitation (VoleskyandHolan, 1995). Type of biomaterials, properties of metal solution chemistry and environmental conditions such as pH influence the mechanism of metal biosorption (Das et al, 2008). 

---