Question

What is soap? How does it act in cleansing clothes?

Hint:

Soaps clean by forming micelles — oil in the center, hydrophilic ends outside — making grease water-washable.

Answer 1

Step 1: Definition.
Soap is the sodium or potassium salt of long-chain fatty acids (such as stearic, palmitic, or oleic acid).
General formula: C$_{17}$H$_{35}$COONa (sodium stearate).
Step 2: Mechanism of cleansing.
Soap molecules have two parts:
- A long non-polar hydrocarbon tail (hydrophobic) that repels water but attracts grease/oil.
- A polar carboxylate head (hydrophilic) that is attracted to water.
Step 3: Action.
When soap is added to water containing dirt or grease:
- The hydrophobic tail dissolves in grease.
- The hydrophilic head faces the water.
This forms spherical aggregates called micelles, which trap the oily dirt inside and wash away with water.
Step 4: Equation.
\[ \text{Fat (Ester)} + \text{NaOH} \xrightarrow{\text{Boil}} \text{Soap} + \text{Glycerol} \]