Question

Alkyl halides are immiscible in water though they are polar because?
A ) they react with water to give alcohol.
B ) they cannot form hydrogen bonds with water.
C ) C-X bond cannot be broken easily.
D ) they are stable compounds and are not reactive.

Answer 1

Hint: A hydrogen bond is formed when hydrogen atom is attached to electronegative nitrogen, oxygen or fluorine atoms. In alkyl halides, hydrogen atoms are attached to only carbon atoms. Hence, alkyl halides cannot form hydrogen bonds.

Complete answer:
> Alkyl halides have polar carbon-halogen bonds. There is a significant difference in electronegativity between carbon and halogen.
> Water is a polar solvent. It dissolves polar solute. This is based on the principle of like-dissolves like. Non polar solvents dissolve nonpolar solute. Based on this principle, alkyl halides should be miscible with water. But however, in reality, alkyl halides are immiscible in water.
> Water forms intermolecular hydrogen bonds which are strong interactions. When alkyl halides are added to water, the strength of interaction between an alkyl halide molecule and a water molecule is weaker than the strength of a hydrogen bond between two water molecules. Thus, alkyl halides can neither form hydrogen bonds nor can they break the hydrogen bonds of water.
> Thus, alkyl halides are immiscible in water though they are polar because they cannot form hydrogen bonds with water.

Hence, the correct answer is the option B ).

Note: Alkyl halides (specially those having six carbon atoms or more) have a long hydrocarbon tail. Hydrocarbon part of alkyl halides is not soluble in water as it is non polar and it is not capable of forming hydrogen bonds. Hence, alkyl halides are not miscible in water.