A student puts a drop of reaction mixture of a saponification reaction first an a blue litmus paper and then on a red litmus paper. He may observe that :

Q: A student puts a drop of reaction mixture of a saponification reaction first an a blue litmus paper and then on a red litmus paper. He may observe that :

The correct option is **(c)**. There is no change in the blue litmus paper and the red litmus paper turns blue.

Also asked in:2016

Carbon and its Compounds

Soaps and Detergents

Options

(a)There is no change in the blue litmus paper and the red litmus paper turns white.

(b)There is no change in the red litmus paper and the blue litmus paper turns red.

(c)There is no change in the blue litmus paper and the red litmus paper turns blue.

(d)No change in colour is observed in both the litmus papers.

Official Answer

The correct option is (c).

There is no change in the blue litmus paper and the red litmus paper turns blue.

SaponificationBasic solutionRed litmus turns blueSoap solutionAlkaline

Hint

Recall that saponification uses a strong alkali like sodium hydroxide ( $NaOH$ ), making the reaction mixture basic in nature.

Quick Oral Answer

The reaction mixture of saponification is basic because soap is a salt of a weak fatty acid and a strong base ( $NaOH$ ), and some unreacted $NaOH$ may also be present. Hence, it turns red litmus paper blue.

Analysis & Explanation

A saponification reaction involves the hydrolysis of fats or oils with a strong base like sodium hydroxide ( $NaOH$ ) to produce soap (sodium salt of fatty acids) and glycerol. Since soap is a salt of a weak acid (fatty acid) and a strong base ( $NaOH$ ), its aqueous solution is alkaline (basic) in nature. Additionally, there may be unreacted sodium hydroxide left in the reaction mixture, which is also strongly basic.

Basic solutions turn red litmus paper blue.
Basic solutions have no effect on blue litmus paper.
Therefore, the red litmus paper turns blue, and the blue litmus paper remains unchanged.

Common Mistakes

1Thinking that soap is acidic and will turn blue litmus red.
2Believing that saponification results in a neutral mixture with no effect on either litmus paper.

Interesting Facts

Soap is a surfactant that lowers the surface tension of water, allowing it to wet surfaces more effectively and wash away grease.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2016?

This question carries 1 mark in the CBSE Class 10 Science 2016 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 "Soaps and Detergents" from CBSE Class 10 Science.

Has this question appeared in other CBSE Science papers?

Yes, a similar question appeared in the 2016 CBSE Class 10 Science paper.

What type of question is this in the CBSE Class 10 Science 2016 paper?

This is a MCQ question from Section B in the CBSE Class 10 Science 2016 paper.