Ask A Scientist Chemistry Archive

Question:  Why doesn't oil and water mix?  What effect does adding detergent do
to a mixture of oil and water?  Why does detergent change the oil and water?
 john j patten

Answer 1:
Since explanations are limited to 25 lines and no pictures (or at least
only very simple ones) I would suggest looking up soap in an encyclopedia.
You might also want to look at surfactant.
To get you started, however, one observation in chemistry is that
molecules dissolve in other molecules that have similar characteristics.
(In particular, the ability or inability to distribute electronic charge
is an important characteristic for solubility.)  Water is a polar
molecule -- that is, electronic charges are localized on specific atoms.
Oil is a non-polar molecule -- electronic charges are de-localized over
all atoms.  Water dissolves other polar molecules and oil dissolves other
non-polar molecules but water does not dissolve oil (and vice-versa).
Soap molecules are large.  At one end they behave like polar molecules 
(electronic charges are isolated) and at the other end they behave like
non-polar molecules (electronic charges are de-localized).
Now, what happens when you put soap in an oil/water mix?
 gregory r bradburn

Answer 2:  To add to Gregs answer: you might try researching emulsions and
emulsifiers and find out about everyday products that are mixtures of
oil and water.  Good luck!
 michael b lomonaco