5.8:
EDTA: Indirect and Alkalimetric Titration
Like direct, back, and displacement titration, indirect titration is an EDTA titration involving metal ions.
In an indirect titration, anions are quantified by precipitating their insoluble salts with excess metal ions and then either directly titrating the excess metal in the filtrate or extracting and back-titrating the metal in the precipitate with EDTA.
For example, the addition of a known excess of barium ions to a sulfate solution generates a barium sulfate precipitate, which is filtered and washed.
The filtrate containing the excess barium ions is titrated with standard EDTA until the end point is reached.
The last type is alkalimetric titration, which is similar to acid–base titration.
This method involves the addition of disodium EDTA to a metal ion solution, which forms the metal–EDTA complex with the liberation of two equivalents of hydrogen ion.
This hydrogen ion solution is titrated with standard sodium hydroxide using a suitable acid–base indicator to obtain the end-point concentration.
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.