State Raoult’s law for a solution containing non-volatile solute dissolved in volatile solvent.
Answers
Raoult's law states that the relative lowering of vapour pressure of a solution containing a non- volatile solute is equal to the mole fraction of the solute in the solution.
Answer:
The vapour pressure of a solution of a non-volatile solute is equal to the vapour pressure of the pure solvent at that temperature multiplied by its mole fraction.
In equation form:
p
T
=p
B
0
.χ
B
In this equation, p
B
0
is the vapour pressure of the pure solvent at a particular temperature, p
T
is the total pressure of the solution, χ
B
is the mole fraction of the solvent.
For a solution of a volatile solute (A) and solvent (B) total pressure is sum of the partial pressure of the two as:
p
T
=p
A
0
.χ
A
+p
B
0
.χ
B
As χ
A
++χ
B
=1 or χ
A
=1−χ
B
or p
T
=p
A
0
.(1−χ
B
)+p
B
0
.χ
B
p
T
=p
A
0
+(p
B
0
−p
A
0
).χ
B
For non-volatile solute p
A
0
=0
thus p
T
=p
B
0
.χ
B
Limitations of Raoult's law:
1. Intermolecular forces between the solvent and solute components shoul be similar to those betweenindividual molecules
A_A=B-B=A-B
2. The gaseous phase are assumed to behave ideal where ideal gas law can be applied.