New Civilization News: How does soap clean?    
 How does soap clean?35 comments
picture 17 Jul 2005 @ 09:27, by Silvia M.S

Soap is a part of our daily life, it has different shapes and perfumes, it can be solid or liquid... But have you ever thought about how this common substance works? Here is a little explanation. I've used a minimum number of scientific terms, so I hope that everybody can understand it.

How soap cleans? There are substances which can be dissolved in water (salt for example), and others that can't (for example oil). Water and oil don't mix together, so if we try to clean an oily stain from a cloth or from the skin, water is not enough. We need soap.

Soap is formed by molecules with a "head" which likes water (hydrophilic) and a long chain which hates it (hydrophobic).

Because of that dualism, soap molecules act like a diplomat, improving the relationship between water and oil. How? When soap is added to the water, the hydrophilic heads of its molecules stay into the water (they like it!), while the long hydrophobic chains join the oil particles and remain inwards (escaping from the water). In that way, they form circular groups named micellas, with the oily material absorbed inside and trapped.

An emulsion of oil in water is then formed, this means that the oil particles become suspended and dispersed into the water. Thus, those oil particles are liberated from the cloth or the skin, and the emulsion is taken away with the rinsing.

In summary, soap cleans by acting as an emulsifier. It allows oil and water to mix so that oily grime can be removed during rinsing. There are more things involved in this process, but this is the general idea.

Versión en español aquí.

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17 Jul 2005 @ 09:54 by jstarrs : I'll never look at a bar of soap... the same way.
I wonder how it works on swear words though?
Sometimes, when we were kids & spoke bad words, the grown-ups would say "Now wash your mouth out with soap & water!"
I guess you just replace 'greasy particle' in the diagram above with the 'naughty' word?
Of course, one wonders how this {} soap works also.
I like Sandelwood soap the best.  

17 Jul 2005 @ 10:37 by gea : I positively love that explanation!
Silvia, this made my day, truly! Makes you look at things, at a simple bar of soap, in a totally new way! (I´ll be waiting to read more of this stuff, I bet you have more of it!) *grin*  

17 Jul 2005 @ 11:39 by silviamar : :-)
Jeff, exactly! I see that you got the picture! :-)
Gea, sure I have more stuff hehe. It's a pity that at school we were not taught Chemistry in a more practical way, formulas and reactions can be very boring for students.  

18 Jul 2005 @ 06:04 by jazzolog : We Have A Poet To Teach Us Chemistry
No wonder I'm finally interested in learning this stuff. So, I have 2 questions:

1) Why does chemistry class smell so bad?
2) Who was the first human to discover soap?  

18 Jul 2005 @ 08:42 by silviamar : to be a poet, to be a chemist...
that is the question! :-)
Jazzolog,the first question is easy to answer. The chem class smell so bad of course because most of the chemical compounds smell pretty bad and people forget to use the extracting hoods when opening the bottles :-) The worst ones are those very volatile. Hydrocarbons (compounds with carbon-carbon and carbon-hydrogen bonds) smell horrible, as well as the sulfured derivatives, which for example are responsible for the bad breath. When the receptors in our nose receive the impact of the molecules of these compounds, they send an unpleasant stimulus to the brain. Some others, as many esthers, smell pretty good and they are part of many fragances and perfumes.

The second question is more difficult, as nobody really knows the answer. Regarding the origin of soap, there is a legend. It's said that it was discovered by chance in Rome after a heavy rain fall on the slopes of Mount Sapo, the water mixed with the animal fat and ashes around an important sacrificial altar, and then people observed that the mixture was useful to wash skin and clothing. But I think that there is documented use of soap as far back as 2500 B.C. The earliest known evidence of soap use are Babylonian clay cylinders dating from 2800 BC containing a soap-like substance.

Questions are always welcomed :-)  

10 Aug 2005 @ 17:39 by konchock : LINDO JABONCITO
Hola Silviamar, interesante y simple explicacion, nunca se me ocurrió pensar por que el jabon limpia, ahora gracias a ti lo se. Lamento que la enorme mayoria de los participantes de esta red sean de habla inglesa, me cuesta mucho ya que en principio he sido un aotudidacta en idiomas y otras cosas. Bueno, un dia de estos te mando un mensaje presentandome, soy de santiago de chile y mi nombre es moris. gracias y hasta pronto  

11 Aug 2005 @ 07:45 by silviamar : gracias konchock
Me alegro de que te haya gustado el artículo, trato de que la gente entienda que la quimica es muy util en nuestra vida y que está en todas partes :-). Mándame el mensaje cuando quieras, encantada de conocerte.
Había pensado en poner un apartado en mi newslog con los artículos que pongo traducidos al español, pero todavía no sé si sería una buena idea... Un saludo desde España.  

4 Sep 2005 @ 18:37 by Kelly @ : Thanks so much
I've been looking for a simplified way to explain this concept to my middle school students (not being sure myself how soap works).I grealty appreciate your simplicity.  

4 Sep 2005 @ 20:38 by silviamar : I'm glad to hear
that this little article has been useful for somebody! When I have some time, I'll post more :-)  

21 Jan 2007 @ 11:11 by Parminder Singh @ : Helpful
This website and article are very helpful. I was looking for something like this for a long time and I finally found this site. This site helped me out alot for my scince fair project. Thank-you so much and the article is so understandable!!!!!!!!!!!!

Hello! I'm glad that this article has been helpful for you! Thanks for your message. I like to bring science to everybody, so we all can understand better the world where we live :-)  

23 Apr 2007 @ 02:42 by bb @ : thx
TQ.. i need to understand my organic chemistry (II), "lipids". i am comfuse about 'micellas' & 'emulsion'....  

17 Aug 2007 @ 07:49 by Jay Dee @ : Esthers
I have read about the topic, but i don't really follow the saponofication part of the chapter! I know that they have nice smells and the have sumthing to do with extraction of fat!  

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2 Oct 2008 @ 21:46 by Bob Kowal @ : Soap for Science
Your site is awesome!  

I am a fifth grade teacher in Washington State and I am putting together a book on science for students to help them learn science and to make it easier for teachers to teach science.  I am going to use the material in a workshop for teachers.  I would permission to use a few paragraphs from your website.  I will give credit to the site and I have ENCOURAGED teachers to visit your site.  The section I want to use is "How does soap clean?". May I have permission to cite your site and put this to good use for teachers and students? Thank you.

Bob Kowal.  

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thanks !! this was perfect for my school paper.. i got eveything i needed !!! thanks again !!  

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Hello !!
I studied this article, and I really like it, but I would like to know how or why why use the laundryt machine?? How it helps to clean? Is it rreally necesary>???  

1 Mar 2011 @ 17:32 by Omar @ : science
its the best explanation but is this the same as the soap of clothes ????plz answer as soon as possible !  

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