Question

The indicator used in the titration of a strong acid and a strong base is/are:
This question has multiple correct options
A. phenolphthalein
B. methyl orange
C. alizarin yellow
D. red litmus

Answer 1

We know that titration is the process that helps in calculation of concentration of an analyte given in a mixture. In analytical chemistry, titration is very helpful. There are many types of titration, such as redox titration, acid base titration, precipitation titration and complexometric titration.

Complete step by step answer:

Let’s first understand the acid base titration.

We know that classification of acid (strong or weak) is based on the amount of dissociation of acids to give hydrogen ions in aqueous solution. If an acid solution whose concentration is known is titrated against a base (strong), the concentration of the acid can be calculated considering that neutralization reaction reaches completion. So, in this case, the strong base is the titrant (standard solution) and the acid solution is titrate.

Now, we understand the role of indicator in titration. An indicator detects the end point. When the reaction is completed, the colour of the reaction transforms due to the presence of the indicator.

Now, come to the question. We have to choose the indicator for titration of a strong acid and strong base. In this case any indicator that has pH range 3.5 to 10 is capable of identification of equivalence point or end point. So, among the given options, methyl orange and phenolphthalein can be used as indicators in acid base titration.

Hence, option A and B are the correct answer.

Note:
In case of very weak acid, the detection of the end point is difficult. So, titration of salt of weak acid against a strong acid is done because the conjugate base of a weak acid is a strong base. For example, acetic acid $\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COOH}}} \right)$ is a weak acid but its salt, sodium acetate $\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{COONa}}} \right)$ is a weak base.