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What is soap made of?


Soaps are made of molecules that are both fat and water soluble. The molecule has a long hydrocarbon tail that allows it to dissolve grease, and a polar head that is water soluble.

A soap molecule. The grey, red, and white balls represent carbon, oxygen, and hydrogen atoms, respectively. The sodium ion near the negatively charged oxygen atoms is not shown.
The head is the sodium or potassium salt of an organic acid.

How do you make a molecule like this? Animal fat contains them, chemically bound to a small three-armed molecule called glycerol. The links between each of the three acid molecules and the glycerol are easily broken in a hot, alkaline solution:
+ 3 NaOH

+
A glyceride (three fatty acids bound to a glycerol) three soap moleculesglycerol
+ 3 NaOH 3 RCOO- Na++

This reaction was used to make soap by treating animal fat with wood ash (which contain a high concentration of potassium hydroxide and potassium carbonate) long before the chemistry of the process was understood.

Author: Fred Senese senese@antoine.frostburg.edu



General Chemistry Online! What is soap made of?

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/consumer/faq/making-soap.shtml