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Litmus Paper

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Last updated date: 04th Mar 2024
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Litmus Paper: An Introduction

As we have learned previously that acids are sour substances and turn blue litmus solution into red litmus solution, whereas, bases are bitter substances and turn red litmus solution into blue litmus solution. But do you know what litmus paper is? How does it turn blue to red or red to blue in colour? How does it respond with acids and bases? In this article, we are going to learn about the litmus paper, its functions, its uses and how it responds with acids and bases.


What is Litmus Paper?

Litmus paper is basically an indicator which is used to distinguish acids from bases as we cannot taste everything to identify if it is an acid or a base. As it indicates the presence of acid or base in a solution, it is also called an acid-base indicator. A litmus paper is made up of wood cellulose paper and litmus. Litmus is a purple dye and it is extracted from lichen plants which belong to the division Thallophyta.

Purple and Blue Litmus Paper


Purple and Blue Litmus Paper


Litmus Paper Colours

Litmus paper is made up of using litmus which is a purple dye but it is available in three different colour varieties which are red litmus paper, blue litmus paper and purple litmus paper.

Red, Blue and Purple Litmus Paper


Red, Blue and Purple Litmus Paper

Purple Litmus Paper:- Purple litmus paper remains purple with the solution having neutral pH, turns red with the solution having acidic pH and turns blue with the solution having basic pH.


Blue Litmus Paper:- Blue litmus paper remains unchanged blue or sometimes purple with the solution having neutral pH, turns red with the solution having acidic pH and turns dark blue with the solution having pH above 8.3.


Red Litmus Paper:- Red litmus paper remains unchanged red or sometimes purple with the solution having neutral pH, turns blue with the solution having basic pH and turns dark red with the solution having pH below 4.5.


Litmus Paper Tests for Acids

Litmus paper is a natural indicator and it can be used to determine whether the given solution is acidic or not. In order to test the acids with the help of litmus paper, the followings steps needed to be followed:

Step-1: Take the unknown solution in the beaker.

Step-2: Take a strip of purple litmus paper or blue litmus paper both are suitable.

Step-3: Now, dip the tip of the purple or blue litmus paper in the respective solution.

If the purple litmus paper or blue litmus paper turns red, then the given solution is acidic.

Blue Litmus Paper Dipped in Acid


Blue Litmus Paper Dipped in Acid


Litmus Paper Tests for Bases

Litmus paper is a natural indicator and it can be used to determine whether the given solution is basic or not. In order to test the bases with the help of litmus paper, the followings steps needed to be followed:

Step-1: Take the unknown solution in the beaker.

Step-2: Take a strip of purple litmus paper or red litmus paper both are suitable.

Step-3: Now, dip the tip of the litmus paper in the respective solution.

If the purple litmus paper or red litmus paper turns blue, then the given solution is basic.

Red Litmus Paper Dipped in Base


Red Litmus Paper Dipped in Base


Use of Litmus Paper

The main use of a litmus paper is to determine the nature of the given solution. Litmus paper is used to test the acidity or basicity of a solution but, in order to determine the nature of gases, wet litmus powder is used. All litmus paper can act as a pH paper, but all pH paper cannot act as a litmus paper.


Conclusion

Litmus paper is a natural indicator which is used to distinguish acids from bases. It is made up of purple dye which is extracted from lichen plants. Litmus paper is available in three different colours which are purple, red and blue. A purple litmus paper turns red if the given solution is acidic and turns blue if the given solution is basic in nature. In order to test whether the given solution is acidic or basic using litmus paper, take the respective solution in the beaker and dip the tip of the litmus paper in the solution. If the litmus paper turns red, then the solution is acidic, if it turns blue then the solution is basic and if it remains unchanged, then the solution is neutral. The main use of a litmus paper is to distinguish an acid solution from a basic solution.

Competitive Exams after 12th Science

FAQs on Litmus Paper

1. What are the limitations of a litmus paper?

Although litmus paper is an easy and quick method to test the nature of the substance, it has several limitations and thus, does not fulfil the requirements of a good indicator. Litmus paper can only indicate the nature of the substance i.e. whether it is an acid or a base and does not show the pH which is one of the important factors.

2. Can the litmus paper be reused?

A litmus paper can be reused again. When a litmus paper turns red it can be used as a red litmus paper and when it turns blue, it can be used as a blue litmus paper for testing the substances only when it is completely dried.

3. Is there any substitute for litmus paper?

As a substitute for litmus paper, red cabbage juice can be used to detect the presence of acids or bases. Also, dyes such as orcein and azolitmin are good substitutes for litmus paper.