why will water not mix easily with oil?

Question

1-nonpolar water molecules are attracted to each other more strongly than to oil molecules
2-polar water molecules are attracted to each other more strongly than to oil molecules
3-polar water molecules are attracted to nonpolar oil molecules
4-polar oil molecules are attracted to each other more strongly than to water molecules

Answer 1

Water is polar and oil is non-polar. They don't mix

Answer 2

Molecular interaction
Water is held together by hydrogen bonds and can interact efficiently with anything that has well developed permanent charges; that's why it can dissolve electrolytes so well.

Oils on the other hand are non polar, simply because the difference between the electronegativities of H and C are so small. These molecules interact by London (of van der Waals) dispersion forces and are induced dipole - induced dipole interactions. These interactions become stronger as more molecules are bound together, at least up to some critical size. These interactions are also strongest between molecules with similar polarizabilities.

The interactions between the oil and water molecules are not strong, the oil can't hydrogen bond as it is non -polar and water can't form strong London forces to the oil; it has a different polarizability.

Size of molecules
Now, a second part to this is that water molecules are much smaller than most other molecules, so to accommodate oil molecules, many water molecules have to have their hydrogen bonds broken.

Related topics
There is a further, somewhat less well understood, part to this story. When water has to surround non-polar parts of molecules it seems to form cage like structures, where the water molecules on the surface of the cavity form 4 hydrogen bonds to neighboring water molecules. These structures can be seen in the crystal structures of certain hydrated electrolytes, called "clathrates". In solution this is called hydrophobic hydration and is still a subject of research.

Perhaps most amazing is the formation of "gas hydrates" where, for example, methane + water mixtures form solids. You can find about these by searching the web for "gas hydrate"

"Water and oil" and biology
The most interesting place where this difference between non-polar "hydrophobic" and polar "hydrophilic" molecules is in biology where nature uses these two in a myriad of ways: fats, which should stay in place, are oily, while sugars, that need to be moved quickly around the body, are very hydrophilic; cell walls are formed by amphiphiles, one end hydrophilic and the other oily (hydrophobic), trans membrane proteins are anchored in the cell wall by having hydrophobic sidegroups, globular proteins have large amounts of hydrophobic sidegroups that make them fold with these on the inside, away from the water.

It is even believed that prion diseases, like mad cow disease, result from the proteins misfolding, with their hydrophobic groups on the outside, these then become "sticky" towards other prion proteins, which also misfold and stick to the first one, eventually leading to the formation of the characteristic plaques found in these diseases. This is likely to be in many biochemistry textbooks but again can be found on the web.

Answer 3

Hummm....why water doesn't mix with oil?...

http://www.chemistryquestion.com/English/Questions/SpecialistChemistry/15_water_oil.html

Answer 4

small rule of thumb: like dissolves in like.

Answer 5

no, but if you put a little soap with it, it will