Natural Indicators: Meaning, Example, Experiment

Introduction to Acids and Bases: Certain food items like lemon juice, orange juice, curd and vinegar taste sour. It is so because they contain acids. It means that the chemical nature of these substances is acidic. The word acid is derived from the Latin word acere, which means sour. The acids in these items are natural acids, i.e. they inherently possess the acidic quality. 

Another domestic example of learning bases and acids is baking soda. If it does not taste sour, then it means that it is not acidic. Baking soda is bitter, and rubbing its mixture between your fingers feels soapy. The bitter taste and soapy feel of these substances makes them bases, and they are considered basic in nature. 

What Is a Natural Indicator?

In cases where every substance cannot be tasted, there should be a method to determine its nature. Certain types of substances are utilised in such instances to determine whether a substance is basic, acidic or neutral. These substances are known as indicators. The indicators change their natural colour based on the nature of the solution they are brought in contact with. The indicators which are found naturally are known as Natural Indicators. Some natural indicators are the litmus test, china rose petals, turmeric etc.

A Natural Indicator is a chemical compound that helps us determine whether the nature of a particular substance is acidic or basic, by changing its colour. The most common natural indicator is a litmus, which is extracted from the lichens. It is purplish in colour in distilled water. When it is added to an acidic solution, the colour of the litmus turns red. When it is inserted in a basic solution, it turns blue in colour. Thus, a natural indicator help in determining whether a given solution is acidic or basic.

Natural Indicators Around Us

Turmeric is an excellent natural indicator. Mix some turmeric powder with water and make a paste. Put it on a filter paper to make turmeric paper. Once the paper is dried, you can use it as a litmus paper to test the acidic nature of a substance. This is why a cloth on which turmeric spills turns red when it comes in contact with soap, as soap is acidic.

There are flowers that like hydrangeas, that can find whether the soil is acidic or basic. Such flowers turn blue in colour if the soil is acidic in nature, purple if the soil is neutral in nature and turn pink if the soil is basic. Also, the brightness of the color depends on the level of acid or base in the soil. The soil which is very acidic gives dark blue flowers. The soil which is highly basic gives dark pink flowers. Such natural indicators are utilised to determine the hydrogen ions (H+) and hydroxyl ions (OH-) present in a solution.

Also, olfactory indicators can change their odour. The most common examples of olfactory indicators are vanilla extract, onion, garlic, etc.

Importance of Natural Indicators

In chemistry, biology, water purification, agricultural practices, nutrition, civil engineering, afforestation, water treatment, oceanography, environmental science, medicine, agronomy, and many other fields, determining acidity or basicity of a substance is crucial.
Students can do their litmus test using daily commodities commonly found in our homes. Below is an easy experiment to determine whether red cabbage is a natural indicator:

Natural Indicators Experiment

Aim: To determine a natural indicator using red cabbage.
Objective of the experiment: To find out if red cabbage is a natural indicator.
Experiment steps: 

• Step 1: Cut some red cabbage and put it in a mixer or a grinder.
• Step 2: Add some water in the jar and grind it until a juicy substance is prepared.
• Step 3: Strain this mixture into a vessel.
• Step 4: Take a few different items like milk, lemon, vinegar, bleach, ammonia, etc and mix them with the red cabbage solution you just created.
• Step 5: The colour of the substance added will change according to its nature of acidity, neutrality or basicity.

Observation of the experiment: The acidic substances change the natural color of the solution from purple to pink or red, depending on the acidity. Substances that are neutral turn the purple solution to blue. Substances which are basic, change the color of the purple solution to green or yellow.
Inference of the experiment: From the above experiment, it can be inferred that a red cabbage is a natural indicator.

Conclusion About Acids, Bases and Natural Indicators

From the above information, it can be concluded that:

1. Almost all acids are sour in taste. 
2. Almost all bases are soapy to touch bitter in taste. 
3. Acidic substances turn a blue litmus into red. 
4. Basic substances turn a red litmus into blue. 
5. Substances that are neither acidic nor basic are neutral in nature. 
6. The solutions that determine the nature of substances whether they are acidic, basic and neutral, are known as indicators. 
7. When an acid and a base neutralise each other the end result is a salt, which can be acidic, basic or neutral in nature.

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