The Science of Making Soap

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In this article we focus on the basics of soap making. Labmuffin Beauty Science has a great article that goes into more detail on the science behind soap-making, which we suggest as further reading.

The traditional method of making soap combines lye (a very basic/alkali substance) with oils and fats.

Chemical Reactions

Although lye and oils/fats are naturally-sourced ingredients (for example, lye can be produced from the ash left over from burning wood), they are still chemicals, and when combined they react together to create soap!

The reaction that produces soap is called saponification, and is what happens naturally when the lye and oils/fats are combined.

3Lye + 1Triglyceride = 1Glycerin + 3Soap

First, the lye and fats/oils break apart into their constituent parts. Lye is NaOH, sodium hydroxide, and is comprised of a sodium ion (Na+) bonded to a hydroxyl ion (OH). The oils/fats are triglycerides, which are made up of three fatty acid chains bonded to a glycerol/glycerin molecule.

After the lye and triglycerides break apart, the free constituents of lye combine with the free constituents of the triglycerides. The lye lends its hydroxyl group to the glycerol, producing a neutral glycerin molecule. And, the sodium ions from the lye bind to the free fatty acids to produce sodium salts! Sodium salts = soap!

A similar process occurs when making liquid soap, but using KOH, potassium hydroxide, instead of sodium hydroxide. What results are potassium salts which still = soap (just soap in a slightly more liquid form)!