Complexometric Titration Curve Equations

A general titration curve equation can be derived from the mass balance equation for the ligand, i.e., to state that the total ligand concentration is the sum of the bound and free ligand concentrations. By the bound ligand is meant the ligand incorporated into the metal complex(es). Thus, for Ag  

Bound Ligand = [FeCp] + 2[FeCl2T + 3[FeCl3] + [FeCl4 ] 

The concentration of each of these species is given by the aC product which, in turn, depends on the value of a single variable, [L]. To express the relationship that total ligand concentration. Cl, is comprised of bound and free ligand concentrations, we can write 

It is useful to compare Equation 9-3 with Equations 8-6 and 8-7. An interesting analogy links the base, which is capable of binding a number of protons, to the metal ion, which is capable of coordinating a number of ligands. Comparing nCg to iiCf and [H ] to [L], the only difference between Equations 8-6 and 9-3 is the absence of [OH ]. In metal complex-ation, water is not a direct participant hence, there is no [OH j. 

Consider an idealized titration (no metal complexation or pH effects on ligand or metal) of 50 mL of 0.003 M Zn + with 0.01 M Na2H2Y(EDTA) and draw the titration curve. Develop the spreadsheet by block filling A with log[Y ] values from -18 to -3 in 0.3 increments. In successive columns, place values of [Y ], with the help of Equation 

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Rearranging Equation 17 and plotting vs. (Cm/(Cl — Cm) ) results in a linear relationship for which the slope is equal to k/Kuif- From the latter portion of the complexometric titration curve where Cm is greater than Cl, a value of k can be obtained. In this region of the titration curve, fa is a linear function of Cm, that is, fa equals kCu-... 

In this chapter, equations will be developed for complexometric titration curves along similar lines used in the previous chapter for Bronsted acid-... 

As shown in Chapter 8, selected individual points in complexometric titration curves can be calculated without recourse to the titration curve equation by (a) performing the reaction stoichiometry at the desired point, (b) recognizing the type of equilibrium calculation represented by the... 

This approach is effective not only for calculations involving individual solutions. The PBE and other balance equations apply to titration curve calculations as well. A single, easily derived, equation suffices to describe all points on a titration curve, be it for acid-base, complexometric, redox, or precipitation titrations. 

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