Details

The following shows how to determine equivalence by colorimetry using a color indicator.

With the volume of (in mL) added to the solution of at the unknown initial solution , we have the following results:

Here (in mL) is the volume of the solution of .

(in mol/L) is the unknown concentration of that we need to find.

(in mol/L) is the known concentration of .

(in mL) is the volume of used to reach equilibrium with .

When , the concentration of the couple is negligible, so the potential measured is that of the couple /:

.

When , the couple determines the measured potential:

.

The change of the potential near the equivalence point can be used to determine the equilibrium volume . Then the unknown concentration can be calculated using (mol/L).

This Demonstration was based on the electrochemistry course (Cours LC102) for first-year students at University Pierre Marie Curie (Paris).