Question

Which if the following indicator can be used for titration?
A. Phenolphthalein
B. Bromothymol blue
C. Methyl orange
D. All of the above

Answer 1

We all know what the titration means. It is a technique to determine the concentration of a solution by calculating the volume of one solution which reacts with another solution. A solution of known concentration to another solution of unknown concentration, but known volume.

Complete step by step solution:
The basic principle of titration is the complete reaction between the titrant of known concentration and analyte. Analyte is a solution whose concentration is unknown and volume is known. Titrant is a solution whose concentration is known.
Titration involves, initially, the standardization of solution. This is done by measuring the concentration of a solution.
Indicator is an additional substance which helps in the detection of completion of the titration process. End point indicates the completion of the titration.
There are several types of indicators-methyl orange, phenolphthalein, cresol red, thymol blue, etc.
Organic compounds are generally used in acid-base titrations. Within a certain ${\text{pH}}$ range, indicators change their color.
The theory of acid-base indicators has been explained using two different theories-Ostwald’s theory and Quinonoid theory.
Based on Ostwald’s theory, color change occurs because the acid-base indicator gets ionized. While based on Quinonoid theory, color change is due to the tautomeric forms of these indicators.
Thus, we can say that all of the given compounds are examples of indicators used for titration.

Hence the correct option is D.

Note: The color change and ${\text{pH}}$ of some indicators have been given in the table below:

Indicator	${\text{pH}}$ range	Color change
Methyl orange	$3.2 - 4.5$	Pink to yellow
Methyl red	$4.4 - 6.5$	Red to yellow
Litmus	$5.5 - 7.5$	Red to blue
Phenol red	$6.8 - 8.4$	Yellow to red
Phenolphthalein	$8.3 - 10.5$	Colorless to pink