Natural Indicators: Examples, Types and Definition

Natural Indicators: An acid-base indicator is usually a dye or any substance that helps to differentiate between the two. There are two types of them: artificial indicators and natural indicators. While the artificial indicators are made in a laboratory, the natural indicators are obtained from natural sources such as plants. Some of the common examples of natural indicators include red cabbage, turnip skin, cherries, beetroots and more.

The natural indicators will help individuals distinguish if it is a base or an acid. In the article below, we have provided complete information regarding the acid and bases. By learning about the natural indicators examples, students can easily differentiate whether the substance is acidic or basic. Keep learning more from the article. Scroll down to know more.

What Are Natural Indicators?

A dye that changes colour when inserted in an acid or base is called an indicator. The dye changes colour when mixed with the substance. Some of the commonly used synthetic indicators are phenolphthalein, methyl orange, and methyl red.

Indicators found in nature, mostly derived from plants, to test whether a substance is acidic or basic, are called natural indicators. Litmus, china rose, red cabbage, turmeric etc., are some of the common natural indicators.

Litmus as Indicator

Litmus is one of the most commonly used natural indicators used for identifying acids and bases in the laboratory. Litmus is a naturally occurring indicator. Litmus solution is a purple dye extracted from lichen, a plant belonging to the thallophyta family. Litmus is purple in colour while mixed in a neutral solution. However, it becomes red when mixed in an acidic solution and blue when mixed in a basic solution.

Litmus is used for testing acidic and basic solutions in two ways: it is either used in the form of a litmus solution or in the form of strips of litmus paper called blue litmus paper and red litmus paper. Litmus solution is further classified into red litmus and blue litmus solutions. We get Blue litmus solution by making the purple litmus extract acidic, and red litmus solution by making the litmus extract alkaline.

Using a Litmus indicator is the currently most commonly used method in laboratories for testing acids and bases.

1. Acids turn blue litmus to red
2. Bases turn red litmus to blue

Testing a substance with litmus and observing the colour change that occurs is a simple way to determine whether a substance is acidic or basic.

(a) If adding a drop of a substance turns blue litmus paper red, then the substance is acidic. For example, if we add a drop of lemon juice to blue litmus paper, it turns red. This shows that lemon juice is acidic in nature or lemon juice contains acid in it.

(b) If adding a drop of a substance turns red litmus paper into blue colour, then the substance is basic or alkaline in nature. Sodium hydroxide solution, for instance, changes red litmus to blue, indicating that sodium hydroxide solution is basic in nature. In other words, sodium hydroxide contains alkali or base.

Turmeric as Indicator

Turmeric is another very good natural indicator. Turmeric is a bright yellow powder derived from the turmeric plant. The Hindi name for turmeric is ‘haldi’. Turmeric naturally contains a yellow dye. However, when mixed in a basic solution, it turns red in colour. Turmeric is used as an indicator in the form of turmeric paper.

How to Prepare Turmeric Paper?

Mix a little turmeric powder with water to make a paste. Spread the paste that you prepared on blotting or filter paper to make turmeric paper. After the paper has dried, cut it into \(3-4\) strips. Now the turmeric paper is ready for use as an indicator.

Even though Turmeric paper can be used as an indicator in a basic solution, it doesn’t work in an acidic solution because:

1. Turmeric paper remains yellow in colour when mixed with an acidic solution
2. However, turmeric paper changes from yellow to red in colour when mixed with basic solutions.

For example, if you put a drop of baking soda solution on a strip of turmeric paper, the yellow turmeric paper turns from yellow to red in colour. This is an indicator that the baking soda solution is basic in nature or it contains alkali. However, upon adding an acidic solution like lemon juice to yellow turmeric paper, the paper remains yellow in colour. Therefore, turmeric paper is not useful to identify whether a substance is acidic in nature.

You must have probably noticed that when a yellow curry stain on a white shirt (due to the presence of turmeric in curry) is scrubbed with soap, it turns red in colour. This happens because the soap solution contains alkali or is basic in nature.

China Rose as Indicator

China rose is another natural indicator used for distinguishing acids from bases. The name of China rose in Hindi is ‘Gudhal’. China rose indicator is a solution that is light pink in colour. It is extracted from the red flowers of the China rose plant and mixed with water. Testing a substance with China rose indicator and noticing the colour change that occurs is an effective method to determine whether a solution is acidic or basic in nature.

1. China rose indicator turns from light pink to Magenta (deep pink) colour when mixed with acidic substances.
2. On the other hand, a basic substance turns China rose indicator from light pink to green in colour.

a. For instance, Lemon juice when mixed with China rose indicator, changes its colour from light pink to magenta (deep pink), indicating that the solution is acidic in nature. In other words, lemon juice contains acid.

b. If baking soda solution is mixed with China rose indicator, the colour of the indicator changes from light pink to green, indicating that baking soda is basic in nature.

Red-cabbage Juice as Natural Indicator

Another commonly used indicator is Red-cabbage juice. It is originally purple in colour. However, its colour changes to red when mixed with an acidic medium and green when mixed with a basic medium.

Study Everything About Red Cabbage Indicator

How to Prepare a Red-Cabbage Juice Indicator?

Finely chop red cabbage. Then, take about \(250\,{\rm{ml}}\) of water in a pan and boil it.  Add the chopped cabbage to it. Allow the mixture to cool for a few minutes. When the liquid has cooled, strain it into clear glasses and discard the cabbage. Red-cabbage juice will be obtained as a dark reddish-purple solution. As a natural indicator, this can be used.

Common Natural Indicators With Their Characteristics Colours

Phenolphthalein as Synthetic indicator

Phenolphthalein is a synthetic (man-made) acid-base indicator.

1. Phenolphthalein indicator is colourless in acid solution
2. Phenolphthalein indicator gives pink colour in basic solution

When we perform the neutralisation reaction of an acid and a base, we will use phenolphthalein as an indicator. Please keep in mind that if we add acid to a base solution that has been coloured pink with a phenolphthalein indicator, the solution will turn colourless. This is due to the fact that acid cancels out the effect of the base.

Methyl Orange as Synthetic Indicator

Methyl orange is an orange dye that retains its colour in a neutral medium. In the acidic medium, the indicator turns red, and in the basic medium, it turns yellow. Both phenolphthalein and methyl orange are synthesised in the laboratory via chemical reactions.

Summary

Natural indicators are the indicators that are obtained from natural sources such as plants. Examples of natural indicators include Litmus, china rose, red cabbage and turmeric. Natural indicators can be used to test acids and bases in the laboratory. They give different colours when put into acid and base.

FAQs on Natural Indicators

Q.1: What are the five natural indicators?

Ans: The five natural indicators are

I. Litmus

II. Turmeric

III. China rose indicator

IV. Red-cabbage juice

V. Beetroot

Q.2: What are natural indicators?

Ans: A natural indicator is a substance found in nature that can tell whether a substance is acidic or basic.

Q.3: What are some examples of natural indicators?

Ans: Some examples of natural indicators are China rose, blueberry, and morning glory.

Q.4: How do you make homemade indicators?

Ans: Preparation of turmeric natural indicator: Make a paste with some turmeric powder and a little water. Place this paste on a blotting or filter paper to make turmeric paper. After the paper has dried, cut it into \(3-4\) strips. The turmeric paper is now ready to be used.

Q.5: What is the best natural indicator?

Ans: The best natural indicator is red cabbage.

Q.6: Is turmeric a natural indicator?

Ans: Yes, turmeric is a natural indicator.

Q.7: Is Onion a natural indicator?

Ans: Onion is an olfactory indicator.