Ready For Boards — Class 12 Chemistry
CBSE 2027 Exam Relevance: Solutions (Chapter 2, Class 12 Chemistry) carries 7-9 marks in CBSE board exam. Colligative properties and Henry’s Law are the most frequently tested topics.
CBSE Class 12 Chemistry Chapter 2 Solutions — Colligative Properties 2027
Chapter 2 (Solutions) is one of the most important chapters in Class 12 Chemistry for CBSE boards. It covers types of solutions, concentration units, Raoult’s Law, colligative properties, and van’t Hoff factor.
Concentration Units — Quick Reference
| Unit | Formula | Temperature Dependent? |
|---|---|---|
| Molarity (M) | Moles solute / L solution | Yes |
| Molality (m) | Moles solute / kg solvent | No |
| Mole Fraction (χ) | Moles component / Total moles | No |
| Mass/Weight % | Mass solute / Mass solution × 100 | No |
Colligative Properties — All Four
Colligative properties depend only on the NUMBER of solute particles, not their nature:
- Relative Lowering of Vapour Pressure: ΔP/P° = χ(solute) = n(solute)/[n(solute)+n(solvent)]
- Elevation of Boiling Point: ΔTb = Kb × m; Kb = ebullioscopic constant
- Depression of Freezing Point: ΔTf = Kf × m; Kf = cryoscopic constant
- Osmotic Pressure: π = iCRT; C = molarity, i = van’t Hoff factor
Van’t Hoff Factor (i): For non-electrolytes: i = 1 | For NaCl: i = 2 | For CaCl₂: i = 3 | For K₂SO₄: i = 3. Actual ‘i’ value is less than theoretical due to incomplete dissociation in concentrated solutions (ion pairing). Only in dilute solutions does i approach theoretical values.
Henry’s Law and Raoult’s Law
Henry’s Law: p = KH × χ (for gases in liquids) — higher KH means lower solubility. Used to explain carbonation of drinks, and the bends in scuba divers.
Raoult’s Law: p = p° × χ (for liquid solutes) — vapour pressure of solution = vapour pressure of pure solvent × mole fraction of solvent.
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