Question

Assertion: Sodium chloride is added to precipitate soap after saponification.
Reason: Hydrolysis of esters of long chain fatty acids by alkali produces soap in colloidal form.
Choose the correct option:
A) Both Assertion and Reason are correct and reason is the correct explanation for Assertion.
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Both Assertion and Reason are incorrect.
D) Assertion is correct but Reason is incorrect.
E) Assertion is incorrect but Reason is correct.

Answer 1

Hint: The answer here is based on the facts about the saponification process which makes use of the hydrolysis process of esters of fatty acids and therefore that forms soap which is precipitated out.

Complete Solution :
We have come across the concept of saponification process in the lower classes of general chemistry part.
We shall now see in detail about the saponification process and its method for the preparation of soaps.
- Saponification process is the one in which there is a conversion of fat, oil or lipid into soap and alcohol with the action of heat in the presence of aqueous alkali.
- Soaps hence formed are nothing but the salts of fatty acids and in this process sodium chloride is added to precipitate soap after the saponification process.
This means that the given assertion is correct.
- Salt is then added to decrease the solubility of soap and this helps to precipitate out the soap from the aqueous solution. The hydrolysis of the esters of long chain fatty acids with alkali produces soap which is the colloidal form.
Thus the given reason is also correct.
- Now, when fatty acids are heated with a solution of sodium hydroxide then they break down to form sodium salt of that particular fatty acid and glycerol along with it and this process is the saponification.
Thus, based on all these facts we can say that assertion and reason are correct but reason is not the correct explanation for assertion.
So, the correct answer is “Option B”.

Note: Note that saponification process involves the numerical called saponification value (SV) or saponification number (SN) which represents the number of milligrams of potassium hydroxide that is required to saponify 1 gram of fat under the specified condition.