Raoult’ s law
Raoult’ s law
o
Raoult’ s law establishes a quantitative relationship between the partial vapour pressure and mole fraction of a solution.
o This law is only for liquid-liquid solution. o
o
The law states that for a solution of volatile liquids, the partial vapour pressure( p) of each component in the solution is directly proportional to its mole fraction( x).
Mathematically, p ∝ x Or p = p 0 x
Where p 0 is the vapour pressure of pure component at the same temperature.
o Thus, for component 1, p1 = p1 0 x1 and for component 2 p2 = p2 0 x
o Let the solvent be represented by 1 and solute be represented by 2. At the point when the solute is non-volatile, just the solvent molecules are present in vapour phase and add to vapour pressure.
Let p1 = vapour pressure of the solvent, x1 = mole fraction,
pi 0 = vapour pressure in the pure state. According to Raoult’ s law
p1 ∝ x1
And p1 = p1 0 x1
Fig. a plot between the vapour pressure and the mole fraction of the solvent is linear