The self indicator is essentially a chemical compound that can indicate the endpoint of titration or any other reaction, with self-participation in the reaction.
What is an indicator?
In chemistry, an indicator is a substance that can be added to indicate the equivalence point of the titration. Color indicators that change color when exposed to acidic or alkaline liquids are commonly used to detect pH. There are two approaches to explain the theory of acid-base indicators: Ostwald's theory and the quinonoid theory.
Natural indicators, artificial indicators, and olfactory indicators are the three categories of indicators used in chemistry. Indicators such as phenolphthalein and methyl orange are commonly used for titration in research, several types of applications, and in the laboratory of science classrooms for practical purposes. As well as a litmus paper (Blue or Red), pH paper, universal indicator, and pH meter are often used to detect the pH of a substance.
| Table of Contents: What is an indicator? What is a self indicator? Example of the self indicator How does KMnO4 acts as a self indicator? Why do we use KMnO4 as a self indicator? |
In the titration procedure, the sample or titrand to be analyzed is poured in a conical flask; two to four drops of a suitable indicator are added, followed by drop-by-drop addition of titrant of known strength or concentration to a burette until the chemical reaction is completed. The indicators can be a self indicator, internal indicator, and external indicator; however, the internal indicators are most commonly used for different types of titration.
What is a self indicator?
A self-indicator is a chemical compound that itself indicates the endpoint of titration or any other reaction involving self-participation. Since the self-indicator indicates the endpoint or equivalence point of reaction, hence there is no need of adding any additional indicator.
Potassium permanganate (KMnO4) is one of the major examples of self-indicator. It is used in oxidation-reduction (redox) titrations that disappear or re-appearing their pink color at the endpoint, as the reaction proceeds.
“A self-indicator is a chemical substance that indicates the titration's endpoint by itself”
Example of the self indicator:
KMNO4 is an example of a self-indicator. Potassium permanganate titrant act as a self-indicator in the presence of a reducing agent, changing color from pink to colorless. It is a versatile and powerful oxidant that may be used to determine the identity of a range of chemicals using direct or indirect titration.
When it is used in redox titration, it is reduced to a brown-colored Mn2+ ion at the endpoint in acidic solutions, and the color change is observable. Since KMNO4 recognizes the endpoint, it does not require any other indicator during the titration.
How does KMnO4 acts as a self indicator?
Because of Mn's +7 oxidation state of Mn, KMnO4 solutions are dark purple. When employed as a titrant, the solution has a permanent pink color after the endpoint is reached and the KMnO4- is in excess (provided that the solution is initially colorless). As a result, KMnO4 serves as its own indicator.
Why do we use KMnO4 as a self indicator?
KMnO4 is a redox indicator. Mn has a wide range of valencies; Whenever Mn changes its valence state, its color changes. As a result, no external indication is required. It can serve as a self-indicator to indicate the endpoint of the reaction.
Frequently asked question (FAQ):
Which indicator is used in permanganometry?
The process does not need an external indicator, Potassium permanganate, which is used in permanganometric titrations, is termed an auto-indicator since its color changes based on the type of reaction.
Why H2SO4 is used in the titration of KMnO4?
Because it is neither an oxidizing nor a reducing agent, dilute H2SO4 (sulfuric acid) is ideal for redox titration.
What is the purpose of indicator in titration?
The objective of an indicator in titration is to detect the titration's endpoint. An indicator is a substance that changes color when exposed to acidic or basic solutions.
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