Why Is Sodium Hydroxide Used To Make Soap

Sodium hydroxide (NaOH), commonly known as lye, is used in the soap-making process to saponify fats and oils. Saponification is a chemical reaction in which an alkali (such as sodium hydroxide) reacts with fats or oils to produce soap and glycerol. The reaction can be represented as follows:

Fat or Oil+NaOH→Soap+Glycerol

In this reaction, the sodium hydroxide (NaOH) breaks down the triglyceride molecules found in fats or oils. Triglycerides consist of three fatty acid chains attached to a glycerol molecule. The sodium hydroxide reacts with the fatty acids, cleaving them from the glycerol backbone. The sodium ions (Na+) combine with the fatty acids to form soap molecules, while the glycerol is released as a byproduct.

The soap molecules have a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. This dual nature allows soap molecules to interact with both water and oil, making them effective for cleaning. The hydrophobic tails attach to grease and oil, while the hydrophilic heads interact with water, allowing the soiled substances to be dispersed and washed away.

After the saponification process is complete, any remaining sodium hydroxide is typically neutralized, ensuring that the final soap product is safe for use on the skin. The process of soap-making using sodium hydroxide is known as cold process soap-making, and it has been employed for centuries to produce soap for various purposes.