Mention the essential material (chemicals) to prepare soap in the laboratory. Describe in brief the test of determining the nature (acidic/alkaline) of the reaction mixture of saponification reaction.

Q: Mention the essential material (chemicals) to prepare soap in the laboratory. Describe in brief the test of determining the nature (acidic/alkaline) of the reaction mixture of saponification reaction.

1. **Essential materials (chemicals) required to prepare soap in the laboratory:** - **Vegetable oil** (such as castor oil, coconut oil, or cottonseed oil) - **Sodium hydroxide ($NaOH$)** (caustic soda) - **Sodium chloride ($NaCl$)** (common salt, used to precipitate the soap out of the solution) 2. **Test to determine the nature of the reaction mixture:** - Take a small amount of the reaction mixture and dissolve it in distilled water to make a solution. - Dip a strip of red litmus paper into this solution. The red litmus paper turns blue. - Dip a strip of blue litmus paper into the solution. The blue litmus paper remains blue. - **Conclusion:** Since the reaction mixture turns red litmus blue, it is **alkaline (basic)** in nature. This is because soap is a salt of a strong base ($NaOH$) and a weak organic acid (fatty acid), which undergoes hydrolysis in water to release hydroxyl ions ($OH^-$).

Also asked in:2017

Carbon and its Compounds

Saponification and preparation of soap

Official Answer

Essential materials (chemicals) required to prepare soap in the laboratory:

Vegetable oil (such as castor oil, coconut oil, or cottonseed oil)
Sodium hydroxide ( $NaOH$ ) (caustic soda)
Sodium chloride ( $NaCl$ ) (common salt, used to precipitate the soap out of the solution)

Test to determine the nature of the reaction mixture:

Take a small amount of the reaction mixture and dissolve it in distilled water to make a solution.
Dip a strip of red litmus paper into this solution. The red litmus paper turns blue.
Dip a strip of blue litmus paper into the solution. The blue litmus paper remains blue.
Conclusion: Since the reaction mixture turns red litmus blue, it is alkaline (basic) in nature. This is because soap is a salt of a strong base ( $NaOH$ ) and a weak organic acid (fatty acid), which undergoes hydrolysis in water to release hydroxyl ions ( $OH^-$ ).

Vegetable oilSodium hydroxideSodium chlorideRed litmus turns blueAlkalineBasic

Marking Scheme

11 mark for listing the essential chemicals (vegetable oil, sodium hydroxide, and sodium chloride).
21 mark for describing the litmus test (red litmus turning blue) and concluding that the mixture is alkaline/basic.

Hint

Soap is prepared by reacting an ester (oil/fat) with a strong base. Soap solutions are basic in nature.

Quick Oral Answer

We add common salt ( $NaCl$ ) during soap preparation to decrease the solubility of soap, causing it to precipitate out of the solution (a process known as 'salting out').

Common Mistakes

1Forgetting to mention sodium chloride (common salt) which is essential for precipitating the soap, or stating that soap is acidic.

Interesting Facts

Saponification literally means 'soap-making' from the Latin word 'sapo', which means soap.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2017?

This question carries 2 marks in the CBSE Class 10 Science 2017 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Saponification and preparation of soap" from CBSE Class 10 Science.

Has this question appeared in other CBSE Science papers?

Yes, a similar question appeared in the 2017 CBSE Class 10 Science paper.

What type of question is this in the CBSE Class 10 Science 2017 paper?

This is a Short Answer question from Section B in the CBSE Class 10 Science 2017 paper.