How do you determine the end point in a titration?

The end point in a titration is determined by observing a colour change in the indicator used.

In a titration, the end point is the point at which the reaction between the titrant and the analyte is complete. This is typically indicated by a colour change in the solution, which is caused by an indicator. An indicator is a substance that changes colour at (or near) the equivalence point of the reaction. The equivalence point is the point at which the stoichiometric amount of titrant has been added to the analyte.

The choice of indicator is crucial in determining the end point accurately. The indicator must be chosen such that its pH range falls within the sharp change of the pH curve at the equivalence point. For example, in a strong acid-strong base titration, phenolphthalein (which changes colour between pH 8.2 and 10) or bromothymol blue (which changes colour between pH 6.0 and 7.6) can be used.

During the titration, the titrant is added to the analyte until the indicator changes colour. This colour change signals that the reaction is complete, and thus the end point of the titration has been reached. The volume of titrant added to reach the end point is then used to calculate the concentration of the analyte.

However, it's important to note that the end point is not always the exact equivalence point. There may be a slight difference between the two, known as the titration error. This is because the indicator doesn't change colour exactly at the equivalence point, but over a range of pH values. Despite this, with careful selection of the indicator and precise execution of the titration, this error can be minimised.

In conclusion, the end point in a titration is determined by the colour change of an appropriate indicator. This signifies the completion of the reaction between the titrant and the analyte, allowing for the calculation of the analyte's concentration.