An aqueous solution of sucrose is 0.5 molal. What is the vapour pressure of water above this solutio — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

A 0.5 molal solution contains 0.5 moles of sucrose in 1000 g of water. Moles of water N = 1000 / 18 = 55.56 mol. Mole fraction of sucrose X_sucrose = 0.5 / (0.5 + 55.56) = 0.5 / 56.06 ≈ 0.00892. Using Raoult's law: (P^o - P) / P^o = X_sucrose => (25.0 - P) / 25.0 = 0.00892 => 25.0 - P = 0.223 mm Hg => P = 24.78 mm Hg ≈ 24.8 mm Hg.