The vapour pressure of water at room temperature is lowered by 5% on dissolving a non-volatile solut — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

A lowering of 5% means (P^o - P) / P^o = X_solute = 0.05. This means the mole fraction of solute is 0.05, and the mole fraction of water is X_water = 0.95. Molality (m) is given by: m = (X_solute / X_water) * (1000 / M_water) = (0.05 / 0.95) * (1000 / 18) ≈ 0.05263 * 55.56 ≈ 2.92 m.