Complexometric EDTA Titration Curves

Now that we know something about EDTA s chemical properties, we are ready to evaluate its utility as a titrant for the analysis of metal ions. To do so we need to know the shape of a complexometric EDTA titration curve. In Section 9B we saw that an acid-base titration curve shows the change in pH following the addition of titrant. The analogous result for a titration with EDTA shows the change in pM, where M is the metal ion, as a function of the volume of EDTA. In this section we learn how to calculate the titration curve. We then show how to quickly sketch the titration curve using a minimum number of calculations. 

Since the titration is carried out at a pH of 10, some of the EDTA is present in forms other than Y . In addition, the presence of NH3 means that the EDTA must compete for the Cd +. To evaluate the titration curve, therefore, we must use the appropriate conditional formation constant. Erom Tables 9.12 and 9.14 we find that ay4- is 0.35 at a pH of 10, and that acd + is 0.0881 when the 

Because K is so large, we treat the titration reaction as though it proceeds to completion. 

The first task in calculating the titration curve is to determine the volume of EDTA needed to reach the equivalence point. At the equivalence point we know that 

Before the equivalence point, Cd + is in excess, and pCd is determined by the concentration of free Cd + remaining in solution. Not all the untitrated Cd + is free (some is complexed with NH3), so we will have to account for the presence of NH3. Eor example, after adding 5.0 mL of EDTA, the total concentration of Cd + is 

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How to sketch an EDTA complexometric titration curve see text for explanation. 

Mg in fertilizers is based on such proceedings thereof has been applied on multiple occasions. In milk fermentation, where the samples were dried, calcined in a furnace at 600 °C, the ash was dissolved in 0.03 M HCl, the solution was centrifuged and the supernatant was thus analyzed . The complexometric method for determination of Ca(II) and Mg(II) can be carried out in a single titration with EDTA in alkaline solution, using a Ca-ISE for potentiometric determination of two endpoints. This is accomplished on digitally plotting pCa values measured by the ISE as a function of the volume V of titrant added to the aliquot of analyte the first and second inflection points of the curve mark the Ca(II) and Mg(n) equivalences, respectively. ... 

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