Answer
Boiling Point Elevation and the van’t Hoff Factor
Boiling-point elevation (ΔTb) is a colligative property and depends on the concentration of solute particles. It is directly proportional to the product of:
- i – the van’t Hoff factor (number of particles a solute dissociates into)
- m – the molality (or approximate molarity for dilute solutions)
ΔTb ∝ i × m
Examples of van’t Hoff Factor (i):
- Urea and Glucose: Non-electrolytes that do not dissociate. i = 1
- KNO₃: Dissociates into K⁺ and NO₃⁻. i ≈ 2
- Na₂SO₄: Dissociates into 2 Na⁺ and 1 SO₄²⁻. i ≈ 3
Conclusion: The greater the van’t Hoff factor (i), the higher the boiling point elevation.
Na₂SO₄ causes the largest elevation, so it gives the highest boiling point among the solutions listed.
Na₂SO₄ causes the largest elevation, so it gives the highest boiling point among the solutions listed.