Chemical species distribution diagram

A graphical representation of the equilibria involved in this type of systems is a plot of the distribution of the species containing M vs pL. This is called a chemical species distribution diagram it can be calculated by defining the equations of the distribution... 

These functions are monotonic (i.e., increasing or decreasing in a continuous fashion) with respect to [L] (or to pL) for the first and last species in the equilibria involved they show a maximum for the intermediate species (called ampholytes). The resulting chemical species distribution diagrams can easily be constructed by introducing these equations in a spreadsheet (e.g., Excel). See Examples 2.5 and 2.6. T/pical examples can be found in the educational literature, and several programs are available for these calculations (see, for example, Kim, 2003). 

Example 2.6 Calculate and draw the chemical-species distribution diagram for the Cu(II)-NH3 system, using the following log values of the global constants for the four sequential equilibria involved 4.10, 7.60, 10.50, and 12.50. Here, pL = pNH3, and M = Cu2+. 

The pH of a system determines the reactions that define the concentration of many dissolved chemical species in water containing salts and minerals, supplied by weathering reactions, rain, runoff, and lixiviating processes. The pH is a key parameter for biological growth and for the sustainment of life for the different aquatic flora and fauna species. As discussed in Chapter 2 the contribution of the different species will affect the final pH and vice versa (i.e., the pH on its own often determines the form of the species present). That is why the distribution diagrams of chemical species are frequently defined as functions of pH (Section 2.1.2). In summary, the main environmental processes that affect the pH and the alkalinity of natural waters include ... 

Thus, one can see that the original definition of local hardness, with ( ) = pC I/N nicely embodies electrostatic effects. Far away from the nuclei the local hardness becomes proportional to the electrostatic potential generated by the molecular charge distribution. Since contour diagrams of molecular electrostatic potentials have been widely used to analyze the chemical reactivity of a great number of chemical species [31], it is to be expected that the local hardness index provided by Eq. (15) will incorporate additional effects, and this way it may become a very useful reactivity index. 

Environmental phase distributions of elements or inorganic chemicals usually involve different chemical species and therefore speciation reactions. For example, different species of an element such as mercury have different vapor pressure and solubility. Elemental mercury, Hg(0), is fairly volatile and only sparingly soluble in water, whereas oxidized Hg(II) complexes are much less volatile but more water soluble. The distribution of mercury among the phases of air, water, and solid will thus depend on its speciation, which in turn is influenced by variable conditions of the environment, including pH, redox conditions, and the presence of other chemical species. This is approached quantitatively using equilibrium reaction constants for the various speciation reactions and illustrated using distribution diagrams that delineate the major prevalent species as a function of pH or pE, or both. 

The flrst term of G is the main contribution and represents a modified Huggins-%-parameter concept. The second term increases tvith the width of the chemical distribution and with the magnitude of Au,p, which is a measure of the intramolecular interactions between the monor units a and p of the copolymer species. Owing to this term of a pure liquid (molten) copolymer (ipn = 1), G does not vanish, so that if Au,p > 0, a molten copolymer may separate into two phases. This effect and its influence on the phase diagram will be discussed in more detail in Sect. 3.3.2. 

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