Why oil does not dissolve in water?

Answer 1

Water dissolves substances because it's hydrogen bonds make it a polar molecule. Thus, the positive and negative ends of the water molecules attract the negative and positive ends (respectively) of substances, thus pulling them apart and dissolving the substance.

Oil, however, is a nonpolar substance, so it is not attracted to the polarity of water.

Answer 2

Oil doesn't dissolve in water for a couple of reasons. First, water is polar, meaning that it has a partial positive charge on one side and a partial negative charge on the other side. Because of this, it dissolves substances that are charged or polar themselves, since the positive charges of the substance would be drawn to the negative oxygen and the negative charges would be drawn to the positive hydrogen. The water molecules would pull them apart and/or surround them in a way that separates them. Oil isn't charged like that, since hydrocarbons aren't polar. (Maybe the ends of the oil molecules might have that, but the hydrocarbon parts of the molecules are so long that the percentage of the molecule that would have a polar part is negligible). Hydrocarbons tend to huddle together and are called hydophobic (avoid water). The lack of polarity/charge prevents water from pulling them apart. A second reason is that oil is less dense than water, so it will float on top of water, rather than mix at the same level.