Question

Derive the relationship between the relative lowering of vapour pressure and mole fraction of the solute.

Answer 1

P_solution ∝ x_A by Raoult’s law. where x_A is the mole fraction of the solvent. 

P_solution = k . x_A 

When 

x_A = 1 

k = P⁰_Solvent

P⁰_Solvent = partial pressure of pure solvent 

P_solution = P⁰_solvent . x_A

where 

x_B = mole fraction of the solute 

x_A + x_B = 1 

x_B = 1 – x_A