Chemistry 2004 JAMB Past Questions - Question 50: In the production of soap, concentrated sodium chloride solution is added to

Correct Answer

B

Explanation

In the production of soap, concentrated sodium chloride (NaCl) solution is sometimes added to assist in the separation of soap from the reaction mixture. This step is known as salting out or brine washing.

During the soap-making process, a reaction called saponification occurs, where fats or oils react with a strong base (such as sodium hydroxide) to form soap and glycerol. The resulting mixture contains soap, glycerol, and some impurities like excess unreacted fats or oils.

The addition of concentrated sodium chloride solution helps in the separation of soap from the aqueous phase. The sodium chloride increases the ionic strength of the solution, causing the soap molecules to aggregate and form larger clumps. This aggregation is facilitated by the fact that soap molecules have both hydrophobic (water-repelling) and hydrophilic (water-attracting) parts. The hydrophobic tails of the soap molecules are drawn together in the presence of salt, reducing their solubility in water.

As a result, the soap molecules come out of solution and form a precipitate. This precipitate can be easily separated from the remaining mixture, allowing for the isolation of the soap. The glycerol and other water-soluble impurities remain in the aqueous phase.

After the salting out step, additional purification steps may be carried out to ensure the final soap product meets quality standards. This can include washing the soap with water or other solvents to remove any remaining impurities.