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.