Acid-base titration
Using a colored indicator is a simple method for determining the end point of the titration. The indicator is a chemical whose acid and base forms have different colors. When a colored indicator is dissolved in an acidic solution, the solution changes color when the pH is increased and approaches the pKA of the acid-base pair.
![Attention pictogram](/resources/images/fiches/bases/etalonnage/symbole-warning.png)
To avoid titrating the indicator, do not add too much of it to the solution.
The pH range in which this color change occurs is called the color transition range of a colored indicator.
HInd stands for the acid form and Ind- for the basic form of the colored indicator. The indicator in the solution is involved in a proton transfer equilibrium.
![Attention pictogram](/resources/images/fiches/bases/etalonnage/symbole-warning.png)
To precisely determine the end point, the pH value at the equivalence point must be in the transition region of the indicator.
![Information pictogram](/resources/images/fiches/bases/etalonnage/symbole-ampoule.png)
In certain cases, the acid and basic forms of the analyte of interest have different colors. This makes it possible to determine the end point of the titration without using a colored indicator.
![Information pictogram](/resources/images/fiches/bases/etalonnage/symbole-ampoule.png)
The sensitive color shade of the indicator is the color the solution has in the range of color change.
Examples of acid-base indicators with their color transition change.
![](/resources/images/fiches/bases/titrage/en/Picture1.png)