In the production of soap, concentrated sodium chloride solution is added to

Analysis

This question tests your understanding of the Saponification process, which is the industrial method of manufacturing soap by reacting fats or oils with an alkali (like sodium hydroxide).

Concept: Salting-out

In the soap-making process, the reaction produces a mixture of soap, glycerol, and water. To separate the soap from this mixture, we perform a process called "salting-out."

When concentrated sodium chloride (common salt) solution is added to the mixture, it increases the ionic strength of the solution. Soap is a salt of a long-chain fatty acid. According to the principle of common ion effect and solubility, the presence of a high concentration of $Na^+$ ions from the salt significantly reduces the solubility of the soap in the aqueous layer. As a result, the soap precipitates and floats to the top as a solid curd, making it easy to skim off.

Step-by-Step Solution

1. The Reaction: Fats/Oils + NaOH → Soap + Glycerol.
2. The Problem: At the end of the reaction, the soap is dissolved in the water/glycerol mixture.
3. The Action: We add concentrated sodium chloride (brine).
4. The Effect: The high concentration of ions makes the soap less soluble in the aqueous phase.
5. The Result: The soap "salts out" (precipitates) and separates from the liquid, allowing for collection.

Conclusion

Adding concentrated sodium chloride does not saponify the soap (that is the job of the alkali) nor does it emulsify it. Its primary purpose is to make the soap insoluble so it can be separated from the mixture.

The correct option is B.

Exam Tip

Whenever you see "sodium chloride" in the context of soap production in a JAMB question, immediately associate it with "salting-out" or "decreasing solubility." It is a classic separation technique!