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Acids, Bases and Salts

Natural Indicators Around Us

We know about Acids and Bases . But how do we determine whether a substance is acidic or basic? We have Natural Indicators around us. You probably have a natural indicator in your home right now. Let us find out more about the natural indicators around us. 

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What are Natural Indicators?

Natural Indicator is a type of indicator that can be found naturally and can determine whether the substance is an acidic substance or a basic substance. Some examples of natural indicators are red cabbage, turmeric, grape juice, turnip skin, curry powder, cherries, beetroots, onion, tomato, etc.

Some flowers like hydrangeas can determine the acidity or basicity of the soil. These flowers become blue if the soil is acidic, purple if the soil is neutral and pink if the soil is basic. The intensity of the color depends on the amount of acid or base present in the soil. Soil which is highly acidic bears deep blue flowers, whereas soil which is highly basic yields deep pink flowers.

These natural indicators are used to detect the hydrogen ions (H+) and hydroxyl ions (OH-) in a solution. Olfactory indicators can change their odor. Some examples of olfactory indicators are onion, vanilla extract, clove oil, etc.

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Importance of Indicators

It is important to determine the nature of a substance because it is essential in biology, chemistry, civil engineering, water purification, agriculture, forestry, food science, environmental science, water treatment, oceanography, medicine, nutrition, agronomy, etc.

Even litmus is extracted from lichens. It is a water-soluble mixture of different dyes. It is then absorbed onto filter paper to produce one of the oldest forms of pH indicator, used to test materials for acidity or basicity.

Experiment

Aim: Create a natural indicator using red cabbage.

Objective: To find out whether red cabbage is a natural indicator.

Experiment: 

  1. Chop some red cabbage and put it in a mixer or a blender.
  2. Add water to it and mix it until a juice is prepared.
  3. Strain this mixture into a glass.
  4. Take different substances like lemon, milk, vinegar, ammonia, bleach etc and mix it with the red cabbage solution.
  5. The color of the substance will change according to their acidity of basicity.

Observation: Acidic substances change the color of the solution from purple to red or pink. Neutral substances turn the purple solution to blue. Basic substances change the color of the purple solution to green or yellow.

Conclusion: Therefore, we can say that red cabbage is a natural indicator.

Question For You

Q1. What is the pH value of seawater? Is it acidic, basic or neutral in nature?

  1. less than two, it is highly acidic
  2. more than ten, it is highly basic
  3. between 7 – 8.5, it is neutral or slightly basic
  4. between 5.5. – 7, it is neutral or slightly acidic

Ans. The correct answer is option ‘b’. The value of seawater is between 7 to 8.4. Ideally, the sea water is neutral or slightly basic.

Q2. What is the pH level of the human body? Is it acidic, basic or neutral?

  1.  Less than 7, acidic
  2. 7, Neutral
  3. More than 7, basic
  4. None of the above

Ans: The pH value of a normal body is ideally 7.4 which is on the alkaline side of neutral and human blood is usually between 7.35 to 7.45 and of human saliva is 7.5.

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