Question

Why alkyl halides though polar are immiscible with water ?

Answer 1

Both alkyl halides and water are polar molecules.The intermolecular force of attractions between two alkyl halide molecules is dipole-dipole attraction. While The intermolecular force of attractions between two water molecules is by hydrogen bonding. When alkyl halides are mixed with water a new force of attraction between the alkyl halides and water comes into play, this new force of attraction is much weaker than the forces of attractions already existing between two alkylhalide and two water molecules respectively. This is the reason that alkyl halides, though polar, are immiscible with water.

OR

To be miscible with water, the solute-water force of attraction must be stronger than the solute-solute and water-water forces of attraction. Alkyl halides are polar molecules and so held together by dipole-dipole interactions. Similarly, strong H-bonds exist between the water molecules. The new force of attraction between the alkyl halides and water molecules is weaker than the alkyl halide-alkyl halide and water-water forces of attraction. Hence, alkyl halides (though polar) are immiscible with water.