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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
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
To precisely determine the end point, the pH value at the equivalence point must be in the transition region of the indicator.

Information pictogram
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
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.
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