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Indicators and their Examples
2023-01-06 17:58:47

Indicators and their Examples

What is an Indicator?

An indicator is a chemical substance that modifies colour based on an acid or base. Indicators are typically made of plant pigments and have a mild acidic or basic nature.

Need of Indicator

Many different chemicals are kept in the laboratory. All of the chemicals look similar. Some of them can be salts, bases, or acids. To recognize the chemicals, the labels are attached on the bottles, but to know their nature means whether it is a base or acid indicator is needed. Indicators are really useful to describe the result of a chemical reaction, whether it is acid or base.

What are Acids?

Any hydrogen-containing substance that can give a proton to another is considered to be an acid. Acids typically have a sour taste.

What are Bases?

Any substance that can receive a hydrogen ion released by an acid is referred to as a base. Bases typically have a bitter taste.

Categories of Indicators

There are three categories of indicators that are olfactory indicators, natural indicators and synthetic indicators.

1. Natural Indicators

  1. These indicators are typically found in the environment.
  2. They are generally obtained from plants.
  3. Litmus, China roses, red cabbage, turmeric, and beets are some examples of natural indicators.

Examples of Natural Indicators

1) Litmus as an indicator

Litmus is a frequently utilized as indicator. It is created from the lichen plant. Litmus turns purple when dipped into a neutral solution.

  1. Blue litmus paper
    • Acidic action: Blue litmus paper changes from blue to red when dipped in an acidic solution.
    • Base's action: When this paper is dipped in the base solution, it stays blue.
  2. Red litmus paper
    • Acidic action:  When this paper is dipped in the acidic solution, it stays red. Citric acid, HCl, and H2SO4 are examples of acids.
    • Base's action: Red litmus paper changes from red to blue when dipped in a base solution. NaOH and KOH are examples of base solutions.

2) Turmeric as an Indicator

  1. Another excellent natural indicator is turmeric.
  2. The colour of turmeric is bright yellow.
  3. When mixed with a base solution, it turns red.
  4. Acidic action: When turmeric is combined with an acidic solution, the colour remains yellow.
  5. Base's action: When mixed with a base solution, it turns red.

3) China rose as an indicator

  1. Hibiscus is the source of the "China rose".
  2. It is a pink solution.
  3. It is generated from the red flower of the hibiscus plant and combined with water.
  4. Acidic action: It turns a magenta colour when combined with an acid.
  5. Base's action: The indicator's colour changes from pink to green when mixed into a base solution.

4) Red cabbage as an indicator

  1. The original colour of red cabbage is purple.
  2. When it isadded to an acidic or base solution, it changes colour.
  3. Acidic action: The colour turns from violet to red when combined with an acidic solution.
  4. Base's action: The red solution becomes blue-green in colour when it is added to the base.

Natural indicators with their colours

Sr.NoIndicator  Colour in Acidic MediumColour in Basic MediumColour in Neutral Medium  
1Litmus  Red  Blue  Purple  
2China Rose  Magenta  Green  Pink  
3Turmeric  Yellow  Red  Yellow  
4Red Cabbage  Red  Green  Violet  

2. Synthetic Indicators

These indicators are generated from artificial substances. Phenolphthalein and methyl orange are two examples of synthetic indicators.

Examples of synthetic indicators

1) Phenolphthalein

  1. This is a colourless solution.
  2. When added to an acidic substance, it does not change its colour.
  3. When it is added to the base substance, the solution becomes pink.

2) Methyl Orange

  1. Its colour is orange.
  2. This is another widely used synthetic indicator.
  3. Acidic action:  It turns reddish-orange when mixed with acid.
  4. Base's action: It turns yellow when mixed with base substance.

Synthetic indicators with their colours:

Sr.No   Indicator   Colour in Acid   Colour in Base  
1Methyl orange   Red  Yellow  
2Phenolphthalein  Colourless  Pink  

3. Olfactory Indicators

An olfactory indicator is a substance whose smell changes depending on whether it is mixed with an acid or base solution.

Examples of olfactory indicators

1) Onion Extract: It retains its strong smell when combined with acid but loses all smell when combined with the base solution.

2) Vanilla Extract: In an acidic solution, it retains its aroma; and it loses that aroma in a base solution.

Olfactory indicators with their smell

Sr.NoOlfactory Indicators  Smell in Acid  Smell in Base  
1Onion  Retains smell  Loses Its Smell  
2Clove Oil  Retains smell  Loses Its Smell  
3Vanilla extract  Retains smell  Loses Its Smell  

Summary

  1. To identify between acids and bases, indicators are utilized.
  2. There are three categories of indicators:
    • Olfactory Indicators.
    • Natural Indicator.
    • Synthetic Indicators.
  3. A natural indicator is derived from the environment.
  4. Indicators which are created in a lab are known as synthetic indicators.
  5. Olfactory indicators are those that change the scent in an acid or base solution.