Question

Assertion: Precipitation of soap is made by the addition of salt $\left( {NaCl} \right)$.
Reason: Presence of common ions suppresses the dissociation of weak acid.
(A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
(B) Both Assertion and Reason are correct and Reason is not the correct explanation for Assertion
(C) Assertion is correct but reason is incorrect
(D) Both Assertion and Reason are incorrect

Answer 1

To solve this question, we must first understand the concept behind the precipitation of Soap. The common-ion effect refers to the decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate. Then we need to assess the reasons causing the precipitation and then match that reason with the given reason and then only we can conclude the correct answer.

Complete step by step answer:
Before we move forward with the solution of this given question, let us first understand some basic concepts:
Precipitation: As we know that, there are many common types of reactions that occur in aqueous solutions. The precipitation reaction is one of them, which results in the formation of precipitate (insoluble product).
Therefore, the precipitate is the insoluble solid that forms during the chemical reaction and separates out in solution.
Step 1: Since, Addition of $NaCl$ increases the polarity of the solution, and the acid's long hydrocarbon chain is non-polar, so the micelles get precipitated out.
The salt reacts with the water that would go toward acting as a solvent for the organic molecule. The inorganic salt is more "thirsty" than the organic molecule and deprives the soap of sufficient water to keep it soluble. This causes the soap to precipitate.
Step 2: Since, from step 1 we can clearly conclude that Using $NaCl$ soap can be precipitated. Hence the assertion is correct.
And we also know that, Common ion effect is for weak electrolytes, where it suppresses the dissociation of weak acid. So, the statement reason in the question is also correct.
Step 3: But, we can observe that the Reason provided does not give any kind of explanation about the assertion.
And hence, we can conclude that Both Assertion and Reason are correct and Reason is not the correct explanation for Assertion
So, clearly we can conclude that the correct answer is Option (B).

Note:
Soap scum or lime soap is a type of white solid composed of calcium stearate, magnesium stearate, and similar alkali metal derivatives of fatty acids. These materials are formed by the addition of soap and other anionic surfactants to hard water. An example of a reaction that forms a precipitate is the reaction that takes place between dissolved soap and hard water. Hard water has certain minerals dissolved in it.