1. What are Colligative Properties?

  1. Colligative properties depend only on the number of solute particles in a solution, not their nature.
  2. The four main colligative properties are:
    • Relative lowering of vapor pressure
    • Boiling point elevation
    • Freezing point depression
    • Osmotic pressure

2. Osmotic Pressure

  1. 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.
  2. Osmotic pressure is the pressure required to stop osmosis.
  3. 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
  4. Applications include reverse osmosis for water purification and medical uses like intravenous fluids.

3. Boiling Point Elevation

  1. The boiling point of a liquid increases when a non-volatile solute is added.
  2. Boiling point elevation is proportional to the molality of the solution.
  3. 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
  4. Applications include antifreeze in car radiators to prevent overheating.

4. Freezing Point Depression

  1. The freezing point of a liquid decreases when a non-volatile solute is added.
  2. Freezing point depression is proportional to the molality of the solution.
  3. 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
  4. Applications include using salt on icy roads to lower the freezing point of water.

5. Key Points

  1. Colligative properties depend only on the number of solute particles.
  2. Osmotic pressure follows the formula π = iCRT.
  3. Both boiling point elevation and freezing point depression are directly proportional to the molality of the solution.
  4. Van’t Hoff factor accounts for dissociation or association of solute particles.
  5. Applications of these properties include reverse osmosis, antifreeze, and de-icing of roads.

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