Question

Sol. [Key Concept: Aqueous solution with the highest boiling point (ΔTb ∝ i·m, van't Hoff factor)] Elevation of boiling point ΔTᵇ = i·Kᵇ·m is a colligative property, so the solution with the largest van't Hoff factor i × molality boils highest. 0.01 M Na₂SO₄ → 2Na⁺ + SO₄²⁻ gives i = 3 (i·m = 0.03); 0.01 M KNO₃ → i = 2 (0.02); 0.01 M urea and 0.015 M glucose are non-electrolytes, i = 1 (0.01 and 0.015). Hence 0.01 M Na₂SO₄ has the highest boiling point.