Question

What is the function of an indicator in a titration?

Answer 1

Hint: Titration is the method employed in the quantitative analysis of any substance. This analysis usually tells us the concentration and strength in terms of molarity or molality of any chemical compound. Indicators are compounds that are added to the analyte solutions in which titrant is added.

Complete answer:
Titration is the quantitative analysis of any sample. The titration can be acid – base type usually, but it can also be redox or other type. An indicator is used in the process of titration. This is added in the analyte, which is added in the conical flask, and to this the titrant from the burette is added.
Indicator is the substance that changes or imparts certain color at the stoichiometric end point of the titration. This means when a certain concentration of the acid or a base is completely neutralized, then at the end point we observe a color change.
For example, in an acid base titration, if we take NaOH in the burette, and add known amount of HCl with known concentration, then according to the equation,
$NaOH(aq)+HCl(aq)\to NaCl(aq)+H_{2}O(l)$
The neutralization between NaOH and HCl is the basis of titration. Here the equivalence point or the end point will be when all the number of moles of an acid is neutralized or added to the base. Then, the pH will be at 7.0, like for this strong acid and strong base titration.
An acid – base titration, uses phenolphthalein as an indicator, that changes its color over the pH of 8.3 – 10. In basic solutions, it will impart a permanent pink color, while in acidic solutions it will impart a clear permanent solution.
Hence, indicators in a titration are used to identify the equivalence or the end point of a reaction where pH change occurs.

Note:
Apart from phenolphthalein, methylene orange is also used as an indicator that changes color when pH changes. It has red color in acidic solution, and a yellow color in basic solution. It is used for titration of acids. The titration of strong acids and strong bases has an equivalence point at pH = 7. Weak acid and strong bases have equivalence points at pH > 7. While, strong acid and weak base titrations have equivalence points at pH < 7.