EDTA complexes formation constants

EDTA complexes of trivalent metals can be extracted successively with liquid anion exchangers such as Aliquat 336-S by careful pH control. Mixtures of lanthanides can be separated by exploiting differences in their EDTA complex formation constants. 

Chromium ir)-EDTA complex (formation constant 4 x 10 ) is a strong reductant that undergoes rapid reactions. 

Speciation of Pb(II) in Glatt river. The concentrations given for CO2, Pb(II), Cu(II) and [Ca2+] as well as for the pollutants EDTA and NTA are representative of concentrations encountered in this river, The speciation is calculated from the surface complex formation constants determined with the particles of the river and the stability constants of the hydroxo-, carbonate-, NTA- and EDTA-complexes.The presence of [Ca2+] and [Cu2+] is considered. 

The conditional formation constant allows us to look at EDTA complex formation as if the uncomplexed EDTA were all in one form ... 

With the conditional formation constant we can treat EDTA complex formation as if all the free EDTA were in one form. 

The EDTA-metal complexes are rather unique because they always form in 1 1 ratio regardless of the charge on the cation. The EDTA-metal formation constant can be described by the reaction... 

B. (a) Write the reaction whose equilibrium constant is the formation constant for EDTA complex formation and write the algebraic form of Kf. 

Concerning its complex formation constants PPG behaves similarly to EDTA, (except for Pb and Zn ) with the following order... 

The formation constants of EDTA complexes are gathered in Table 11.34. Based on their stability, the EDTA complexes of the most common metal ions may be roughly divided into three groups ... 

TABLE 11.34 Formation Constants of EDTA Complexes at 25°C, Ionic Strength Approaching Zero ... 

Metal—EDTA Formation Constants To illustrate the formation of a metal-EDTA complex consider the reaction between Cd + and EDTA... 

Conditional Metal—Ligand Formation Constants Recognizing EDTA s acid-base properties is important. The formation constant for CdY in equation 9.11 assumes that EDTA is present as Y . If we restrict the pH to levels greater than 12, then equation 9.11 provides an adequate description of the formation of CdY . for pH levels less than 12, however, K overestimates the stability of the CdY complex. 

After the equivalence point, EDTA is in excess, and the concentration of Cd + is determined by the dissociation of the CdY complex. Examining the equation for the complex s conditional formation constant (equation 9.15), we see that to calculate Ccd we must first calculate [CdY ] and Cedxa- After adding 30.0 mb of EDTA, these concentrations are... 

Finding the End Point with a Visual Indicator Most indicators for complexation titrations are organic dyes that form stable complexes with metal ions. These dyes are known as metallochromic indicators. To function as an indicator for an EDTA titration, the metal-indicator complex must possess a color different from that of the uncomplexed indicator. Furthermore, the formation constant for the metal-indicator complex must be less favorable than that for the metal-EDTA complex. 

This reaction will proceed if the metal indicator complex M-In is less stable than the metal-EDTA complex M EDTA. The former dissociates to a limited extent, and during the titration the free metal ions are progressively complexed by the EDTA until ultimately the metal is displaced from the complex M-In to leave the free indicator (In). The stability of the metal-indicator complex may be expressed in terms of the formation constant (or indicator constant) Ku ... 

The basis for the toxicological activity of this substance is the reaction of cobalt ion with cyanide ion to form a relatively nontoxic and stable ion complex. The hexacyanocobaltate ion contains a Co2+ central metal ion with six cyanide ions as ligands. This coordination complex involves six coordinate covalent bonds whereby each cyanide ion supplies a pair of electrons to form each covalent bond with the central cobalt ion. The formation constant for the hexacyanocobaltate ion is even larger than for dicobalt EDTA,3 and thus the cobalt ion preferentially exchanges an EDTA ligand for six cyano ligands ... 

TABLE 9.1 Formation Constants for Complexes of EDTA with Metal Cations at 25°C... 

The larger the formation constant, K, the more likely the M - EDTA complex is to form and the fewer free metal ions remain. 

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