Q26
1 markMCQSection B

While studying the saponification reaction, what do you observe when you mix an equal amount of colourless vegetable oil and 20% aqueous solution of NaOH in a beaker?

Also asked in:2017
Chemical Reactions and Equations
Exothermic Reactions

Options

(A)The colour of the mixture has become dark brown
(B)A brisk effervescence is taking place in the beaker
(C)The outer surface of the beaker has become hot
(D)The outer surface of the beaker has become cold
Official Answer

Option C is correct because saponification is an exothermic reaction, which releases heat energy, causing the temperature of the reaction mixture to rise and making the outer surface of the beaker feel hot.

exothermicheat releasedbeaker becomes hotsaponification

Marking Scheme

  • 11 Mark for selecting the correct option (C) with the correct reasoning that saponification is an exothermic reaction.

Hint

Think about whether saponification (soap-making) releases or absorbs heat, and whether any gas is produced during this reaction.

Quick Oral Answer

Saponification is an exothermic reaction. When vegetable oil reacts with sodium hydroxide, heat is released, which raises the temperature of the mixture and makes the beaker feel hot.

Analysis & Explanation

Saponification is the alkaline hydrolysis of an ester (vegetable oil or fat) using a strong base like sodium hydroxide (NaOHNaOH) to form soap and glycerol. This chemical reaction is highly exothermic, meaning it releases heat energy into the surroundings. Consequently, the temperature of the reaction mixture increases, making the outer surface of the beaker feel hot to the touch (Option C).


Why other options are incorrect:

  • Option A: The mixture does not turn dark brown; it typically forms a whitish or creamy suspension of soap.
  • Option B: No gas is evolved during saponification, so there is no brisk effervescence.
  • Option D: The reaction is exothermic (releases heat), not endothermic (which would absorb heat and make the beaker cold).

Common Mistakes

  1. 1Confusing exothermic with endothermic reactions and choosing Option D.
  2. 2Expecting gas evolution and choosing Option B.

Interesting Facts

Saponification has been used for thousands of years to make soap from animal fats or vegetable oils and wood ash (which contains potassium carbonate).

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Frequently Asked Questions

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

This question carries 1 mark in the CBSE Class 10 Science 2017 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Exothermic Reactions" 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 MCQ question from Section B in the CBSE Class 10 Science 2017 paper.