Why can't oil and water mix together ?

Answer 1

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.

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 2

oil and water are immisible liquid. oil will form a layer above water. oil is also lighter than water so oil and water cannot be mix together .

Answer 3

Probably both. When you open the radiator cap if cracked air will come up. White smoke comes out too. Ive heard of steel seal or bars headgasket fix for cars that the work is over the value of car but have never tried it. Most mechanics say that that is only temporary and better if replaced.

Answer 4

simple. oil is less dense than water. that's why it floats. they don't mix because of their varying densities....

Answer 5

They have different densities and the molecules cannot bond together.

Answer 6

oil is nonpolar : it can only dissolve in nonpolar solvents lote tetrachloromethane
water is polar: it can only dissolve polar substances