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1. What are Colligative Properties?
- Colligative properties depend only on the number of solute particles in a solution, not their nature.
- The four main colligative properties are:
- Relative lowering of vapor pressure
- Boiling point elevation
- Freezing point depression
- Osmotic pressure
2. Osmotic Pressure
- Osmosis is the movement of solvent molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration.
- Osmotic pressure is the pressure required to stop osmosis.
- It is given by the formula: π = iCRT, where:
- π = osmotic pressure
- i = van’t Hoff factor
- C = molar concentration
- R = gas constant
- T = temperature in Kelvin
- Applications include reverse osmosis for water purification and medical uses like intravenous fluids.
3. Boiling Point Elevation
- The boiling point of a liquid increases when a non-volatile solute is added.
- Boiling point elevation is proportional to the molality of the solution.
- The formula is: ΔTb = iKb m, where:
- ΔTb = boiling point elevation
- i = van’t Hoff factor
- Kb = boiling point elevation constant
- m = molality of the solution
- Applications include antifreeze in car radiators to prevent overheating.
4. Freezing Point Depression
- The freezing point of a liquid decreases when a non-volatile solute is added.
- Freezing point depression is proportional to the molality of the solution.
- The formula is: ΔTf = iKf m, where:
- ΔTf = freezing point depression
- i = van’t Hoff factor
- Kf = freezing point depression constant
- m = molality of the solution
- Applications include using salt on icy roads to lower the freezing point of water.
5. Key Points
- Colligative properties depend only on the number of solute particles.
- Osmotic pressure follows the formula π = iCRT.
- Both boiling point elevation and freezing point depression are directly proportional to the molality of the solution.
- Van’t Hoff factor accounts for dissociation or association of solute particles.
- Applications of these properties include reverse osmosis, antifreeze, and de-icing of roads.