1. Define molality. Why is it preferred over molarity in temperature-dependent calculations?
Key: Molality = moles of solute per kg solvent. Independent of temperature → reliable in colligative property calculations.
2. State Henry’s law and give one real-life application.
Key: p = KH·x. Solubility of CO₂ in cold drinks increases at high pressure → bottling.
3. Define ideal solution. Mention two examples.
Key: Obeys Raoult’s law fully; ΔHmix = 0; ΔVmix = 0. Examples: benzene–toluene, hexane–heptane.
4. What is positive deviation from Raoult’s law? Give an example.
Key: Solute–solvent forces weaker → VP↑ BP↓. Example: ethanol + acetone.
5. What is an azeotrope? Name one minimum-boiling azeotrope.
Key: Constant-boiling mixture; cannot be separated by distillation. Eg: Ethanol–water.
6. Write ΔTb = Kb m. Define each term.
Key: Boiling-point elevation = ebullioscopic constant × molality.
7. Explain osmotic pressure. Why is it best for determining molar mass?
Key: Π = CRT; measurable for dilute solutions; high accuracy.
8. What is van’t Hoff factor? Give values for NaCl and K₂SO₄.
Key: i = observed/calculated property. NaCl ≈ 2; K₂SO₄ ≈ 3 (ideal dissociation).
9. Why does adding salt to ice lower the freezing point?
Key: Solute lowers chemical potential → FP decreases (freezing point depression).
10. Write formula for depression in freezing point and its use in molar mass determination.
Key: ΔTf = Kf m. m = (ΔTf × Wsolvent)/(Kf × Wsolute) → molar mass.