The end point in a titration is established by observing a color change in the chosen indicator.

In the context of a titration, the end point refers to the moment when the reaction between the titrant and the analyte is complete. This completion is typically signified by a color change in the solution, which occurs due to the presence of an indicator. An indicator is a chemical substance that alters its color at or near the equivalence point of the reaction. The equivalence point is defined as the stage at which the stoichiometric amount of titrant has been added to fully react with the analyte.

Selecting the appropriate indicator is vital for accurately determining the end point. The indicator must be chosen so that its pH transition range aligns with the steep change in the pH curve at the equivalence point. For instance, in a titration involving a strong acid and a strong base, indicators such as phenolphthalein, which transitions color between pH $8.2$ and $10$, or bromothymol blue, which changes color between pH $6.0$ and $7.6$, are suitable options.

Throughout the titration process, the titrant is gradually added to the analyte until a color change is observed in the indicator. This change in color indicates that the reaction has reached completion, marking the end point of the titration. The volume of titrant required to achieve this end point is then utilized to calculate the concentration of the analyte.

It is essential to recognize that the end point may not coincide precisely with the equivalence point. A slight discrepancy, known as the titration error, can occur. This discrepancy arises because the indicator does not change color exactly at the equivalence point but rather over a range of pH values. Nevertheless, with careful selection of the indicator and meticulous execution of the titration, this error can be minimized.

In summary, the end point of a titration is determined by the color change of a suitable indicator. This change signifies the completion of the reaction between the titrant and the analyte, enabling the calculation of the analyte’s concentration.