Question

An aqueous solution freezes at -0.2°C. What is the molality of the solution. Determine also the-

(I) elevation in boiling point

(II) Lowering of vapour pressure

Given Kf=1.86°C Kg/mol Kb=0.512°C Kg/mol.

Vapour pressure of water=23.756 mm

Answer 1

delta tf=kf*m
m=delta tf/kf
=0.2/1.86
=0.107 molal

elevation in boiling point
delta tb=kb*m
=0.512*0.107
=0.05°C


Lowering of vapour pressure=23.756*0.107
=2.5411mm