Question

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

Answer 1

Here,

Vapour pressure of the solution at normal boiling point (p₁) = 1.004 bar

Vapour pressure of pure water at normal boiling point

Mass of solute, (w₂) = 2 g

Mass of solvent (water), (w₁) = 98 g

Molar mass of solvent (water), (M₁) = 18 g mol⁻¹

According to Raoult’s law,

= 41.35 g mol⁻¹

Hence, the molar mass of the solute is 41.35 g mol⁻¹.