Chemical indicators are mostly derived from plant pigments that change color in the solutions in which it is present. It plays a crucial role in the field of chemistry to understand the properties of various types of chemical reactions. Most of the chemical indicators tend to change their own color in chemical reactions while some of them change in turbidity.
Most of the indicators are transparent in nature. Chemical indicators create a visible sign (usually, a change in color) during they detect the presence of the threshold concentration of some chemical species like an acid, base, etc. This article shows detailed insight into chemical indicators, discussing their definition, examples, types, and various applications.
Chemical Indicators Definition
Chemical Indicators are those chemical substances in which their presence in chemical reactions helps us to know whether the concentration of a chemical is ideal or not. Indicators are weak bases or weak acids that change in color of the solutions to reveal the characteristics of reactants as well as reactions. The changes in hydrogen ion concentration can be detected easily by indicators.
Chemical Indicators Example
There are many indicators used in the laboratory as well as working fields. Examples: Litmus, Thymol Blue, Phenol Red, phenolphthalein, and methyl orange are all indicators that are commonly used in the laboratory. They change their property like color in acid or base solution to reveal the various characteristics of the solutions.
Chemical Indicators Types
There are mainly three types of indicators namely natural, artificial, and olfactory indicators. The discussion about these types of indicators is given below:
Artificial Indicator: This type of indicator is generally prepared in the laboratory to indicate the strength of solutions. This indicator is also known as a synthetic indicator. They are also used for sterilization processes in the field of medical science.
This type of indicator provides accurate results in various chemical processes. Artificial indicator is expensive as well as difficult to prepare. Examples of artificial indicators are methyl orange, methyl red, and phenolphthalein. Artificial indicators are used very much to identify what is basic and what is acidic.
Natural Indicators: Natural indicators are generally collected from plants and plant products. Natural indicators help us to identify the acidic or basic concentration of a solution. This type of indicator can be prepared easily at a low cost. This indicator does not create any harmful effect on the environment. Examples of natural indicators are litmus, turmeric, China rose, and red cabbage.
Olfactory Indicators: These indicators change their color with smell when come in contact with acidic or basic solutions. The use of this type of indicator is less than the natural and synthetic type indicators.
Olfactory indicators are used in educational and laboratory settings for experiential learning. For example, vanilla essence changes its smell after coming in contact with a basic solution.
Characteristics of Acid-Base Indicators
Acid-base indicators should be chemically pure and not react with other substances in the solution at a general state.
Acid-base indicators should be chemically inert and must not dissociate during the reaction.
Indicators change their color at the equilibrium point or end-point during titration.
The Mechanism of Acid-Base Indicator
If the indicator is made from a weak acid, the acid with its conjugate base shows different type colors. If the indicator is made from a weak base, the base with its conjugate acid shows different type colors.
The general formula for a weak acid is HIn. It reaches an equilibrium state according to the following chemical equation:
HIn (aq) + H2O (l) ↔ In–(aq) + H3O+ (aq)
In the above reaction, HIn(aq) represents an acid that contains a different color from the base In–(aq). When the examined solution contains a lower pH value, then the concentration of the hydronium ion H3O+ is high. As a result, the equilibrium condition is towards the left and produces the color A.
When the examined solution contains a higher pH value, then the concentration of the hydronium ion H3O+ is low. As a result, the equilibrium condition is towards the right and produces the color B.
Phenolphthalein is a well-known weak acid indicator. This indicator is completely colorless but it can form a magenta or red-purple anion after dissociation. The equilibrium reaction shifts to the left in an acidic solution, then the solution turns colorless. When the pH of a solution is increased, the equilibrium reaction state shifts to the right position, and then a magenta color is visible.
The equilibrium constant for an equilibrium reaction can be determined by using the following equation:
KIn = [H3O+][In–] / [HIn]
Where KIn represents the indicator dissociation constant value. The color can be changed at the point when the concentration of the acid and anion base comes to an equal state.
[HIn] = [In–]
It is a very important point when half of the indicator turns into acidic form and the other half indicator turns into conjugate base form.
Importance of Chemical Indicators
Chemical indicators are essential for knowing the acidic concentration in titration.
Chemical indicators play an important role during the process of sterilization.
The acidic and basic characteristics are identified by applying the indicators.
Acid-base titration depends on the indicator mechanism.
Uses of Acid-Base Chemical Indicators
Indicators are used in chemical laboratories to identify the acidic, basic, or neutral characteristics.
Indicators are essential to monitor the change in acidity at the volumetric analysis state in neutralization reactions.
Chemical indicators are used very much to generate signals at the end-point of an acid-base titration.
Indicators are used to test the soil properties as well as the determination of acidic or basic characteristics of the soil sample.
Indicators are used in swimming pool water for measuring the acidity.
Indicators are used to monitor the characteristics of liquid waste.
Frequently Asked Questions (FAQs)
What is an indicator in chemistry?
A chemical indicator changes its to color in solution to express the acidic or basic characteristic of the examined solution.
What are the examples of indicators?
There are many indicators used in different fields. Some common indicators are methyl orange, methyl red, and phenolphthalein.
What are the types of chemical indicators?
There exist three types of chemical indicators namely natural, artificial, and olfactory indicators.
What are the uses of chemical indicators?
Chemical indicators are used for soil testing purposes, swimming pool water testing purposes, and identification purposes of various chemicals.
