The vapour pressure of the solvent is lowered by
the presence of a non-volatile solute in the solution and this lowering of vapour
pressure of the solvent is governed by Raoult’s law, according to which the relative
lowering of vapour pressure of the solvent over a solution is equal to the mole
fraction of a non-volatile solute present in the solution However, in a binary
liquid solution, if both the components of the solution are volatile then another
form of Raoult’s law is used Mathematically, this form of the Raoult’s law is stated
as:
0
0
total
1
2
2
1


p
p x
p x Solutions which obey Raoult’s law over the entire range
of concentration are called ideal solutions