Question

Using Raoult’s law explain how the total vapour pressure over the solution is related to mole fraction of components in the following solutions.

(i) CHCl₃ (l) and CH₂Cl₂(l) 

(ii) NaCl(s) and H₂O (l)

Answer 1

Hint : Discuss the following formulas 

(i) for a binary solution having both components as volatile liquids, the total pressure will be 

p = p₁ = x₁p₁⁰ + x₂p₂⁰ 

= x₁p₁⁰ + (1–x₁)p₂⁰ 

= (p₁⁰ – p₂⁰ )x₁ + p₂⁰ 

p = total vapour pressure 

p₁ = partial vapour pressure of component 1 

p₂ = partial vapour pressure of component 2. 

(ii) For a solution containing non-volatile solute, the Raoult’s law is applicable only to vaporisable component (1) and total vapour pressure is written as 

p = p₁ = x₁p₁⁰