Question

Explain relative lowering of vapour pressure with the help of Roult’s Law and compare it with Henry’s Law?​

Answer 1

1) For dilute solution, Raoult's law of lowering of vapour pressure states that:

(IIT JEE 1985)

(a) the relative lowering of vapour pressure is equal to mole fraction of solute

(b) the vapor pressure of the solution is equal to mole fraction of the solvent

(c) the relative lowering of vapour pressure is proportional to amount of solute

(d) the lowering of vapor pressure is equal to the mole fraction of solute in solution

Logic and Solution:

According to Raoult's law, for dilute solutions containing non volatile solute, the relative lowering of vapor pressure, Δp/po is equal to the mole fraction of solute, X2.

i.e.,

Δp/po = X2

It is a colligative property.

Conclusion:

The correct option is "a".

Extra information:

* The lowering of vapor pressure is proportional to the mole fraction of solute or inversely related to mole fraction of solvent.

* Colligative properties depend only on the number of particles and not on the nature of substances.