attraction

[Primarygun]

I know soap has a polar head and a non-polar head.

Therefore, it can attract water or oil and bring oil to leave a shirt.

How does soap have the attraction with oil?

[pulkit]

It does not actually have attraction for oil.

 

Polar head is hydrophillic and non polar head is hydrophobic.

 

The hydrophobic heads move towards oil or grease only to avoid water.

[Primarygun]

Thank you

[YT2095]

this may help a little to: http://sci-toys.com/ingredients/sodium_stearate.html

 

or just do a seach for "Sodium Stearate"

 

http://www.google.com/search?q=%22sodium+stearate%22&hl=en&lr=&ie=UTF-8&start=0&sa=N

[Firedragon52]

To help further:

http://chemistry.about.com/library/weekly/aa081301a.htm

[VendingMenace]

if i might add a bit...

 

There is a small attrative force between the oil and the non-polar chain of the detergent. This is the so-called Van Der Waals force. It is the weakest of the intermolecular forces and is do to instantaneous dipole interactions between the two molecules.

 

That is to say this; even though the molecule is overall-time-avereaged non polar. When two of these molecules get close enough to eachother their electron clouds interact with eachother. This causes small, instantaneous (and short lived) dipoles to form in the molecule. These dipoles are formed in such a manner that they attrach eachother. And so this is the attractive force between the two.

 

However, this force is quite small. The majority of the effect is what is known as the "Hydrophobic effect." Which is what pulkit elluded to ealier. The way to think about this is that there is a large amount of attraction between polar molecules. So much so that they like to crowed together. When they do this, they will force out of their way any molecules that are not equally attracted to them. Thus, these non-polar molecules are essensially squished around until they find an environment in which they are not be shoved out of they way. Such an invironment would be one in which they are surrounded by molecules that have they same attraction for eachother as for our molecule of interest.

 

So, in the case of detergent, the oil is "pushed" out of the polar, aqueous, solution until it finds a non-polar area to reside in, in this case the micelle formed by detergent molecules.

 

IN the end, the "attractive" force that one would suppose cuases the non-polar part of the detergent to gather oils and greese is really do to a "repellent" force of the aqueous phase (really, it is do to the attractive forces of the polar part of the solution, but close enough for government work). Pretty cool, i think.

 

Anyways, everyone else did a great job answering this too, i just thought i would add me two cents, for whatever it is worth (prolly 1/50 of a dollar).

 

Cool