Natural Indicators: Litmus, Turmeric, China Rose and Red Cabbage

In this blog, we are going to learn about the natural indicators around us such as turmeric, red cabbage and china rose. We will also learn what is litmus and why it is used for.

What is a Litmus?

Litmus is a mixture of natural dyes extracted from lichens. It is the most commonly used indicator. It has a purple color in distilled water. It turns red when added to an acidic solution. It changes to blue when added to a basic solution. Litmus is available both in the form of a solution and in the form of paper strips. Generally, it is available as red and blue litmus paper.

Let us do an activity!

  1. Take a small amount of lemon juice mixed with water in a small cup.
  2. Take one strip of blue litmus paper and one strip of red litmus paper. Put a drop of lemon juice on the red litmus paper with the help of a dropper. What do you observe? There is no change in the color of litmus paper. Now put a drop of some lemon juice on the blue litmus paper. Now, what do you observe? The color of the blue litmus paper turns red. This shows that lemon juice is acidic in nature.
  3. Now we perform the same activity with the other substances such as tap water, detergent solution, aerated drink, soap solution, shampoo, common salt solution, sugar solution, vinegar, baking soda solution, and lime water.
  4. Based on the experiment result, we will find that tap water, detergent solutions, soap solution, shampoo, baking soda solution, and lime water are basic in nature since the red litmus paper turns blue on adding these bases.

Aerated drink and vinegar are acidic in nature, as in this case, the blue litmus paper will turn red. Also, it is very important to note that; the solutions which do not change the color of either red or blue litmus are known as neutral solutions.

Common salt solutions and sugar solutions are neutral solutions.

1. Natural Indicators: Turmeric as an indicator

Take one or two teaspoonfuls of turmeric powder. Make a paste of it using water. Apply the turmeric paste on a filter paper and let it dry. The turmeric paper is ready. Cut thin strips of this turmeric paper. Take one strip and put a drop of soap solution on it. What do you observe? The color of the turmeric paper changes to purple-brown, this is due to the fact that the soap solution is basic in nature.

Similarly, if any drop of the acidic solution is added to the turmeric paper, the turmeric solution stays yellow.

Hence we can conclude that:- Turmeric solution stays yellow in the presence of acids and changes to purple-brown in the presence of bases.

2. Natural Indicators: China Rose as an Indicator

Activity:-

Take some warm water in a beaker. Put some petals of china rose in the water. Cover the beaker and wait for some time till the water becomes colored. Now this colored water can be used as an acid-base indicator. China rose indicator changes to magenta when brought in contact with acids and it changes to green when brought into contact with bases.

Let us use china rose indicator to find whether lemon juice, soda water, vinegar, sugar solution, common salt solution, dilute shampoo solution and sodium hydrogen carbonate solution are acidic or basic or neutral in nature.

Based on the results; We find that lemon juice, vinegar are acidic in nature , whereas soda water, dilute shampoo solution and sodium hydrogen carbonate are basic in nature.

Similarly, Sugar solution and common salt solution are neutral in nature.

3. Natural Indicators: Red Cabbage Juice as indicator

Red cabbage juice is also used as an indicator. Red cabbage juice is of blue-violet color. It becomes red with acidic substances. With basic substances, it becomes green and even yellow.

Read More: Acids and Bases: Definition, Properties, Uses, and Examples

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