Generally speaking only certain molecules will dissolve in water to begin with. The old phrase "like dissolves like" or "birds of a feather flock together" is very true with respect to what degree solutes are soluble or miscible in different solvents. At very low concentrations, almost all molecules are somewhat soluble in all solvents. But by trend, ionic and polar solutes are more soluble in polar solvents and non-polar molecules are soluble in non-polar (mostly organic) solvents. The units of concentration we just discussed are used to describe the degree to which a solute is soluble in a solvent.
When you place a non-polar molecule in a polar solvent (like oil in water) the molecules try to minimize surface contact between them. (like you and a guy with a cold on an elevator). This is actually the basis for the cells in our bodies. The lipids (oily fatty acids) form our cell membranes so that their non-polar tails face inward away from the polar cytoplasm and the polar heads face towards the polar cytoplasm.
