5.8: EDTA: Indirect and Alkalimetric Titration
Unlike direct titration, back-titration, and displacement titration, indirect titration is an EDTA titration method for quantifying anions. In the indirect titration method, anions are precipitated as their insoluble salts with excess metal ions. The filtrate containing the excess metal ions is directly titrated with standard EDTA until the endpoint is achieved. Another approach involves extracting the metal ion and back-titrating with standard EDTA to obtain the endpoint. In this way, the amount of anion is indirectly estimated.
Another EDTA titration method is alkalimetric titration. This titration method is similar to acid–base titration. During the titration, disodium EDTA is added to a metal ion solution, forming the metal–EDTA complex. This process involves the liberation of two equivalents of hydrogen ions in the solution, which is titrated using a base such as standard sodium hydroxide in the presence of appropriate acid–base indicator until the end-point concentration is obtained.
