Question

Why the molecular weight obtained by depression of freezing point is more correct than the molecular weight obtained by elevation of boiling point ?

Answer 1

The depression of freezing point is much accruate method for determination of molar mass because the freezing point is the temperature at which the vapour pressure of the liquid becomes equal to vapour pressure of solid. It is not affected by other external forces.
But boiling point is the temperature at which the vapour pressure of the solvent is equal to atmospheric pressure. So change in atmospheric conditions will change the values and the reading will be inaccurate. For example a change in wind speed will increase/decrease the vapour pressure and hence the boiling point. So the answer obtained by elevation of boiling point is not accurate.