Question

Despite having greater polarity HF boils at lower temperature than water. Why?

Answer 1

Inspite of being polar and able to form 'H' bonds, HF is low boiling because:
1) There is formation only one 'H' bond per molecule which can be broken comparitively more easily (Water has 2 H bonds per molecule and hence is high boiling)

2) If we compare it with other halo acids e.g. HCl which is a gas at R.T, HF due to existence og hydrogen bonds is a low boiling liquid.

Though the strength of a single hydrogen bond in HF is stronger than in H2O but H2O is surrounded by 4 water molecules which form hydrogen bond with H2O whereas in HF, there is only a single HF molecule.

Long story short, H2O have greater number of hydrogen bonds per molecule as compared to HF.