Polarity and solubility
Solubility depends the polarity of substances being mixed.
Non-polar molecules tend to dissolve only in non-polar molecules. Polar molecules tend to dissolve only in polar molecules.
Non-polar molecules are able to interact with other similar molecules through van der Waals forces of attraction.
Polar molecules interact with each other through dipole-dipole interactions, where the positive end of one molecule interacts with the negative end of another molecule.
Polar and non-polar molecules do not interact strongly with each other due to the difference in the types of interactions they can make.
Polar and non-polar molecules usually do not dissolve in one another. Mixing these two types of molecules usually gives two distinct layers.