I3i: Describe the Colligative Properties
Intro
- A solution behaves differently from a pure solvent
- Because particles of solute interfere with physical processes
- COLLIGATIVE PROPERTIES = properties of a solution that depend only on the concentration of solute & not on the type of solute particles
- Adding solute to a solvent with ∆:
- VAPOUR PRESSURE ↓
- BOILING POINT ↑
- FREEZING PT ↓
- OSMOTIC P ↑
Vapour Pressure
- All liquids have a Vapour Pressure
- The molecules on liquid surface are liquid ⮂ gas spontaneously
- No. of gas particles resent determines the Vapour Pressure
- Adding solute → some particles wil occupy the liquid surface SA
- ∴↓ability of some molecules to enter gas phase
- ∴Adding solute = ↓VAPOUR PRESSURE
Boiling Point
- Every solution has a Boiling Pt
- When the liquid irreversibly enters gas phase
- Adding solute particles to solvent
- Blocks molecules going into gas phase
- ∴more heat required
= ↑Boiling Pt
Freezing Point
- The freezing pt/ is the interface liquid ⮂ solid
- For liquid to freeze it must form a lattice
- Adding solute → interferes with solvent particles forming a lattice
- ∴to compensate, the system needs to be at an even lower temp. to freeze
- ∴Freezing pt ↓
Osmotic Pressure ↑
- Osmotic P ∝ of solute particles
- ∴Adding solute to solvent ↑ of solute particles
- ∴↑Osmotic pressure