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Chemical Indicators – Definition, Types, Examples

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Chemical Indicators in Acids, Bases, and Salts are defined as the chemical substances that are used to indicate whether a liquid is an acid or base. All the solutions (liquids) around us can be categorized into three categories that are, Acidic, Basic, Or Neutral. The chemical substances that are used to differentiate these substances are called Chemical Indicators Or simply Indicators.

Here in this article, we will learn about chemical indicator definition, Types of chemical indicator, Natural Indicators, Artificial Indicators, Olifactory Indicators, and others in detail.

What are Chemical Indicators?

Indicators are weak acids or weak bases that show a change in color as the concentration of Hydrogen ions in a solution changes or the pH of a solution changes. The indicators dissociate slightly in the water to form ions. Some examples of indicators are Litmus, Turmeric, Phenolphthalein, etc.

Any material that offers visual evidence of the presence or absence of an acid or an alkali in a solution, generally by a color change is called a chemical indicator. A chemical called Methyl Yellow, for example, gives an alkaline solution a yellow color. When acid is gradually added, the solution remains yellow until all of the alkali has been neutralised, at which point it becomes red.

Chemical Indicator Definition

In chemistry we define an Acid, Base indicator as a substance that changes its colour in Acidic Or Basic solution. Litmus paper is the most common example of the Indicators. We all have seen litimus paper in our Chemistry lab. As the name suggest it is a paper with purple color in neutral solution and it turns red when an acidic solution is added and it turns blue in presence of the basic solution. It is a natural chemical substance that is obtained from Lichens.

Types of Indicators

Indicators are mainly of two categorised into two categories,

  • Natural Indicators
  • Artificial Indicators

Natural Indicators

Natural Indicatora are indicator that are found in nature and can be used to detect whether a material is acidic or basic. Red cabbage, turmeric, grape juice, turnip peel, curry powder, cherries, beetroots, onion, tomato, and other are examples of natural indicatiors.

Hydrangeas a type of plant is a natural indicator that naturally tells the acidity or basisity of the soil. For example, if the soil is acidic, the plants blooms turn blue, purple and if the soil is neutral, and the plants bllons turn pink if the soil is basic. The colour intensity is determined by the quantity of acid or base in the soil. Deep blue flowers bloom in extremely acidic soil, whereas deep pink blooms bloom in strongly basic soil.

Following are some natural indicators that are commonly used,

  • Litimus
  • Turmeric
  • Red Cabbage

Litmus

Litmus is obtained from lichens and is a mixture of water-soluble dyes that are obtained from the lichens. Litmus is generally made into a soluble dye and then absorbed onto a paper that is then called Litmus Paper. The natural colour of litmus is purple. Litmus can be used to test if a compound is an acid or a base.

  • A red litmus paper turns blue in a basic solution and does not show any colour change in acidic solutions.
  • A blue litmus paper turns red in an acidic solution and shows no colour change in a basic solution.
  • Neutral litmus turns red and blue in acidic and basic solutions respectively.

The image added below shows the acid base changes of the Litmus Paper.

Litmus-Paper

Turmeric

Turmeric is a naturally occurring indicator and is commonly known as Haldi. It is bright yellow in colour. Turmeric paste can be used to test for acids or bases. In an acidic medium, turmeric is yellow in colour and does not show any colour change while in a basic solution its colour turns red.

Red Cabbage

Red cabbage is commonly used as a vegetable but its extract can also be used as an indicator. Red cabbage is a natural indicator. Red cabbage contains a pigment Anthocyanin that is responsible for the colour change of red cabbage in an acid or base. Red cabbage extract is used as an indicator. Red cabbage has a deep purple colour naturally.

The red cabbage extract turns red in an acidic medium with a pH < 7 and bluish-green in an alkaline or basic medium with a pH > 7.

China Rose

China Rose is a type of flower and is commonly called Gurhal. It is normally available in the many houses. It is also a natural indicator and is used to distinguish between Acidic and Basic Solution. An extract of the this plant tells us wether the solution is acidic or basic.

  • In acidic solution, the extract of china rose turns Bright Pink or Magenta.
  • In basic solution, the extract of china rose turns Green.

Natural Indicators and Colour Changes

There are various natural indicators that and the table shows the color change in the acidic and basic solution.

Natural Indicator

Color Change

Acidic/Basic Change

Blackberries

Red to Blue Or Voilet

In Basic Solution

Blueberries

Blue to Red

In Acidic Solution

Cherries

Red to Blue

In Basic Solution

Rose Petals

Red to Blue

In Basci Solution

Artificial (or Synthetic) Indicators

Synthetic indicators, often known as artificial indicators, are acid-base indicators that are made from artificial form various chemicals. Following are some artificial or synthetic indicators discussed below,

Methyl Orange

Methyl Orange is an indicator and shows colour change in acidic or basic solution. It is originally orange in colour. Methyl orange can be only used in the case of Mineral Acids and Strong Bases. It cannot identify weak acids or weak bases.

  • In an acidic medium, Methyl Orange turns Red
  • In a basic medium, Methyl Orange turns Yellow

The structure of methyl orange is as shown in the image below,

Phenolphthalein

Phenolphthalein is a water-soluble dye and is dark purple in color. It is used in form of a solution to test for acid and base. It is mostly used in acid-base titrations.

  • In an acidic medium, Phenolphthalein is colorless
  • In a basic medium Phenolphthalein turns light pink in color

The color of phenolphthalein in acidic and basic medium is shown in the image added below,

Apart form these indicators there are some other categories of indicators that shows the acid and base solution without changing their colors they shows the change in acidic and basic solution with change in their smell, they are called Olfactory Indicator. Let’s learn about them in detail in the article below.

Olfactory Indicators

An olfactory indicator is a chemical that changes its scent depending on whether it’s combined with an acidic or basic solution. In the laboratory, olfactory indicators can be used to determine whether a solution is a basic or an acid, a technique known as olfactory titration. Simply defined, olfactory markers are compounds in acid and basic solutions that have distinct odours. For example, vanilla extract, onion and clove oil, and so on have distinct aromas. Olfactory indicators are very helpful to identify acids or bases for visually impaired students.

Some of the olfactory indicators are as follows:

Onion Extract

Onion Extract can be obtained by boiling the water and adding chopped onion into it. When the water cools down, the onion extract is ready. Onion extract shows the change in smell in acid and bases. When it is added to an acid, it retains its pungent smell but in bases, it becomes completely odourless.

Vanilla Extract

Vanilla extract works just like onion extract. It retains its pleasant smell in an acidic solution but loses its smell in a basic medium.

Colors of Indicators in Acidic and Basic Solution

The table added below shows the indicators and their colors in acidic and basic solution respectively.

Indicator

Colour in Acid

Colour in Base

Methyl orange 

Red

Yellow

Phenolphthalein 

Colourless

Pink

Litmus 

Red

Blue

Turmeric 

No change

Reddish Brown

Red cabbage extract 

Red

Bluish Green

Onion extract 

  • No colour change
  • Retains its smell
  • No colour change
  • Becomes odourless 

Vanilla Extract 

  • No colour change 
  • Retains its pleasant smell 
  • No colour change 
  • Loses its smell 

Universal Indicators

The common indicators may or may not show colour change over a wide range of pH but only for a small range. This makes it difficult to identify a range of acids or bases. This problem is solved by universal indicators. Univeral Indicators is a indicator that is used to show color change in a wide range of Acid and Base. They are formed by mixing multiple indicators in a fixed proportion that change their colour over a wide range of pH values.

Importance of Chemical Indicators

Determining wether any substance is Acid or Base is very important for various purposes and Ckemical Indicator help us to identify the nature of the solution. The uses of Indicators are,

  • Chemical Indicators are used to identify end point of a titration reaction.
  • Chemical Indicators are used to identify nature of various solution so that we can neutralize them effectively.
  • Chemical Indicators are used to identify the nature of soil so that we must use the suitable fertilizers, etc.

Read More,

Chemical Indicator – FAQs

1. What is Chemical Indicators Class 10?

An indicator is generally a weak acid or weak base that dissociates in a solution to form ions and show some specific colors. Indicators are used to test whether a medium is acidic or basic in nature.

2. What are Importance of Indicators?

Chemical Indicators are important because,

  • They tells the end point of the titration reaction.
  • They tell the nature of the solution given, etc.

3. What are Different Types of Indicator?

Indicators are generally categorized into two types,

  • Natural Indcator
  • Artificial Indicator

4. An Indicator turned Red in HCl and Blue in NaOH solution. Identify the Indicator.

We know that HCl is acidic in nature and NaOH is basic in nature. As the indicator turned red in acid and blue in base, it is surely litmus.

5. What are Olfactory Indicators?

Olfactory indicators are indicators that change their smell depending upon the acidic or basic nature of the medium. Example: Onion Extract, Vanilla Extract

6. What is a Chemical Indicator Example?

Chemical indicator undergoes color change in acidic and basic solution and the example of chemical indicator is Litmus Paper.

7. What are 3 Common Indicators?

The 3 most common indicators are,

  • Litmus
  • China Rose
  • Turmeric

8. What is pH?

pH is the measure of the concentration of the hydrogen ion in a solution. It is used to define the strength of the Acid and Base solution.

  • pH = 7 (Neutral Soution)
  • pH > 7 (Basic Solution)
  • pH < 7 (Acdic Solution)


Last Updated : 20 Oct, 2023
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