Adsorption Titration
An indicator is added to the solution and can be adsorbed on the surface of a colloidal suspension containing the analyte SEint(s).
This technique relies on the difference in surface charges of the particles before and after the equivalence point.
Before the equivalence point, the Ind- indicator is free in solution, with the same charge as the surface charge of the particles. Thus it is repelled by the particles (electrostatic interaction) and colors the solution.
![](/resources/images/fiches/bases/titrage/en/anim-titrage1.png)
After the equivalence point, the surface charge is reversed. The indicator is adsorbed on the surface of the particles where it forms a precipitate of a different color from that of the free indicator in the solution.
![](/resources/images/fiches/bases/titrage/en/anim-titrage3.png)
![Table showing examples of colored adsorption indicators](/resources/images/fiches/bases/titrage/en/titrage19.png)
This technique is used in particular for the titration of halide ions: I-, Br- and Cl-. n this case, the titrant is the Ag+ ion. As soon as Ag+ is added, a colloidal precipitate of AgI, AgBr or AgCl is formed.