5 important numericals based on all four colligative properties including van’t Hoff factor (i) — aligned with CBSE PYQs and exam style:
1. Relative Lowering of Vapour Pressure (PYQ Style)
Q: 5.85 g of NaCl is dissolved in 100 g of water. Calculate the relative lowering of vapour pressure. (Given: Molar mass of NaCl = 58.5 g/mol, i = 2)
Concepts Involved:
- Mole calculation
- Raoult’s Law
- Use of van’t Hoff factor
2. Elevation of Boiling Point
Q: 3.42 g of sucrose (C₁₂H₂₂O₁₁) is dissolved in 180 g of water. Calculate the elevation in boiling point. (Kb = 0.52 K·kg/mol, Molar mass of sucrose = 342 g/mol)
Concepts Involved:
- Molality
- Non-electrolyte (i = 1)
- ΔTb = i·Kb·m
3. Depression in Freezing Point (CBSE 2020)
Q: 1.8 g of glucose is dissolved in 100 g of water. Calculate depression in freezing point. (Kf = 1.86 K·kg/mol, Molar mass of glucose = 180 g/mol)
4. Osmotic Pressure
Q: Calculate the osmotic pressure of a solution containing 0.5 mol NaCl in 2 L solution at 27°C. (R = 0.0821 L.atm.per mole per K, i = 2)
Concepts Involved:
- π = i·M·R·T
- NaCl dissociation
5. Van’t Hoff Factor (Abnormal Mol. Mass)
Q: 0.1 mol of K₂SO₄ is dissolved in 1 kg water. The freezing point is found to be depressed by 0.488 K. Calculate the van’t Hoff factor (i) and degree of dissociation. (Kf = 1.86 K·kg/mol)
Concepts Involved:
- Use i = ΔTf / (Kf·m)
- K₂SO₄ dissociates into 3 ions → Theoretical i = 3
- Use of degree of dissociation formula
Would you like solutions with step-by-step explanation for these too? CLICK HERE
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