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.
Sample Practice Questions
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Henry's constant Kh for a gas: higher Kh means:
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Answer: Lower solubility of gas
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When a solid solute is dissolved in a liquid, solubility generally increases with:
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Answer: Increasing temperature
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Elevation in boiling point: ΔTb = Kb × m. Kb is:
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Answer: Molal elevation constant (boiling point elevation constant)
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For a solution following Raoult's law with negative deviation:
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Answer: A-B interactions are stronger than A-A and B-B
Practice Questions
Practice 20 randomly selected NEET questions on Solutions. Answers are revealed after each question.
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What are the key concepts in Solutions for NEET?
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.
Which formulae are important for Solutions in NEET?
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.
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