Question

An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at normal boiling point of the solvent. What is the molar mass of the solute?

Answer 1

Vapour pressure of pure water at the boiling point (P°) = 1 atm 1.013 bar 

Vapour pressure of solution P_s = 1.004 bar 

M₁ = 18 g mol^-1 

M₂ = ? 

Mass of solute = W₂ = 2 g 

Mass of solution = 100 g 

Mass of solvent W₁ = 98 g

Applying Raoult’s law for dilute solution