MadSci Network: Chemistry

Re: what is the ingredient in the soap that makes suds?

Date: Mon Jan 31 08:43:06 2000
Posted By: David Barker, Grad student, Organic Chemistry, University of Sydney
Area of science: Chemistry
ID: 949185250.Ch

Most modern soaps and detergents have a few ingredients in them that cause suds. These chemicals are called surfactants and their job is to trap dirt and grease by forming a bubble around the dirt which thereby removes the dirt from the surface it was on.

For some good pictures of soap and how they form bubbles go look at the page I've linked here :Soap Bubbles

Well there are lots of different surfactant chemicals that are found in today's soaps and detergents. I grabbed a few bottles and bars from the cupboard, and a textbook or two, and came up with this small list. You should find one or some of these in your soaps:

Sodium lauryl sulfate.
Sodium C14-16 olefin sulfonate, or anything that has Cxx-xx and sulfonate.
Cocamidopropyl betaine or sometimes glycerine betaine.
Lauryl glucoside, or other glucosides.

All these chemicals have the same sort of structure. They have a charged end that interacts with water and a fatty end that interacts with dirt.

The only other chemical you might like to consider are ones that contain "ethanolamide" in their name, such as cocomonoethanolamide. These chemicals are sometimes found in some soaps , more frequently in washing powders and they are put there to actually increase the amount of foamy suds. Thats because most people believe they need lots of suds and foam to clean, it doesnt actually make much difference if a soap is foamy or not, but we mentally things are getting cleaner if there is foam so thats why these chemicals are sometimes found.

Good luck with you son's project.

David Barker

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