Q13-113CP - Chemistry: Molecular Nature Of Matter And Change

Question

Why don’t soap micelles coagulate and form large globules? Is soap more effective in fresh water or in sea water? Why?

Step-by-Step Solution

Answer

Two polar ends of micelles repel each other and prevent coagulation.

Soap in more effective in fresh water than sea water.

Step 1: Soap micelle

In water, soap molecule is uniquely oriented which helps to keep the hydrocarbon part outside the water. A micelle is a formation that results from the assembly of hydrophobic tails at the core of the cluster, ionic ends at the interior and surface of the cluster, and clusters of molecules.

The soap micelles have nonpolar tails which is present inside the micelles and an ionic head which is present outside the micelles. So, two polar heads of micelles repel each other and prevent the coagulation of micelles.

Step 2: Soap effect on fresh water and sea water

Both sodium and potassium are alkali metals. The relatively high concentration of salt in sea water lowers the solubility of soaps, made with sodium hydroxide, due to the salting out effect. Potassium soap are more soluble in sea water than sodium soap. Fresh water has less salt content, thus soap is more effectively soluble in fresh water.