Question

In the soap micelles:
A ) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.
B ) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.
C ) both the ionic end and the carbon chain are in the interior of the cluster.
D ) both ionic ends and carbon chains are in the exterior of the cluster.

Answer 1

Soap is a sodium salt of fatty acid. Fatty acid has several carbon atoms in its hydrocarbon chain.

Complete answer:
A molecule of soap has two parts, one is hydrophilic and other is hydrophobic. Hydrophilic end is the ionic end and has great affinity for polar water molecules. Electrostatic forces of attraction are present between the polar water molecule and the ionic end of the soap molecule. The hydrophilic part is the exterior part and contains sodium salt of a carboxylic acid as a functional group. Sometimes the functional group is sodium salt of sulfonic acid.
The hydrophobic end or a soap molecule contains a long hydrocarbon chain of a fatty acid or a fatty alcohol. This hydrophobic end has little if any affinity for water. But it has a large affinity for dirt, oil and grease. The hydrophobic part is the interior part and is insoluble in water.
When the dirty cloth is placed into a soap solution, the dirt particles are surrounded by hydrophobic ends and the hydrophilic ends are surrounded by water molecules.
The ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

Hence the correct option is A).

Note: Due to high surface tension, water cannot spread on dirt. Hence, water does not have cleansing ability. When a soap is added to water, it decreases the surface tension of water.