Question

External indicators are added from outside and detects the change in pH value.
A. True
B. False

Answer 1

Hint: As the name suggests, that is “external” which means outside and external indicators usually do not take part in chemical reactions by itself but after the completion of reaction, they tend to change the colour of the solution. So, from its term itself, you can draw a conclusion whether the statement is correct or wrong.


Complete step by step solution:
To answer this, first let's see what is an indicator.
An indicator is a substance which changes the colour of a solution during chemical reaction specially during titration. The main purpose of an indicator is to derive the actual end point for the volumetric as well as complexometric titration.
Generally, indicators can be classified into three categories and these are- self indicator, internal indicator and external indicator.
- Self indicators in general, are not an indicator but these are one of the reacting species of titration, which after completion of a reaction changes the colour of the solution itself.
- Internal indicators are referred to as those indicators that take part in the chemical reaction and after completion of the titration process, it changes the colour of the solution indicating the exact end point.
- External indicators are those types of indicators that never take part in the original chemical reaction but after completion of the chemical reaction, it changes the colour of the solution indicating the end point.
So, from the above statements, we can conclude that external indicators are those which are added from outside of a solution and they tend to change the colour of the solution by themselves not involving in the reaction.
So, the given statement is true.

Hence, the correct option is A.


Note: As the indicators are classified into three categories, you may get confused which indicator has what type of work. So, remember that external indicators never take part in chemical reactions thus termed as external while internal indicators take part in the chemical reactions.