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Solutions
Concentration, colligative properties, osmosis
Key Concepts
- Colligative properties depend on number of solute particles, not their nature
- Raoult's law: vapour pressure of solution is lowered by solute
- Elevation of boiling point and depression of freezing point are colligative
- Osmotic pressure: π = MRT (van't Hoff equation for dilute solutions)
- Van't Hoff factor i > 1 for electrolytes; i < 1 for associated solutes
Important Formulae
| Raoult's law | P_solution = χ_solvent · P°_solvent |
| Boiling point elevation | ΔTb = Kb · m · i |
| Freezing point depression | ΔTf = Kf · m · i |
| Osmotic pressure | π = MRT |
| Relative lowering of vapour pressure | ΔP/P° = χ_solute |
Quick Tips
- For water: Kf = 1.86 K·kg/mol; Kb = 0.52 K·kg/mol.
- Abnormal molar mass: electrolytes dissociate (i > 1), acetic acid in benzene dimerises (i < 1).
- Isotonic solutions have equal osmotic pressure — important in IV drips.
Practice Questions
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