Expert: Leo Carr - 5/7/2006

Question
I was wondering why oil separates from water, I understand that the oil is more dense than the water, but I would like any other info on this subject, Thanks.

Answer
It has to do with their chemical make-up which affects their physical behavior.  Oil is made up of long carbon chains, these long and large molecules usually only contain carbon and hydrogen.  They are considered non-polar. This means they behave like a neutral compound. In addition, the hydrogens will not take part in hydrogen bonding. (which is a characteristic of water molecules).

Water on the other hand is polar.  There is a slight negative charge surrounding the oxygen atom and a partial positive charge around the hydrogen.  This polar action is why solids like sodium chloride, sodium hydroxide, are very soluble in water.  

The oil and water want to get as far apart as possible, thus the separation.