At a pH of 6.6, would we have to check an alpha chart of EDTA in order to determine the actual amount of "usable" EDTA in the solution? I learned in class that only the fully deprotonated form of EDTA can complex with transition metal ions.
Joyce, Both the metal ion and hydrogen ions compete for EDTA. In a buffer at pH 6.6 the fraction of EDTA in the Y-4 form will be small. However, if the binding strength of the metal EDTA complex is very large, it can pull the EDTA away from the hydrogen ions. The product of alpha times the formation constant, Kf, for the EDTA-metal complex gives a “conditional binding constant” for the complex. The bigger that number, the more completely the metal will take all of the EDTA away from the hydrogen ion. A conditional binding constant equal to or greater than 100,000 is usually the value that people accept as complete. That is, all of the original EDTA goes into forming the complex.
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At a pH of 6.6, would we have to check an alpha chart of EDTA in order to determine the actual amount of "usable" EDTA in the solution? I learned in class that only the fully deprotonated form of EDTA can complex with transition metal ions.
Joyce, Both the metal ion and hydrogen ions compete for EDTA. In a buffer at pH 6.6 the fraction of EDTA in the Y-4 form will be small. However, if the binding strength of the metal EDTA complex is very large, it can pull the EDTA away from the hydrogen ions. The product of alpha times the formation constant, Kf, for the EDTA-metal complex gives a “conditional binding constant” for the complex. The bigger that number, the more completely the metal will take all of the EDTA away from the hydrogen ion. A conditional binding constant equal to or greater than 100,000 is usually the value that people accept as complete. That is, all of the original EDTA goes into forming the complex.
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