Colligative Properties Colligative properties depend only on the

Colligative Properties • Colligative properties depend only on the number of solute particles present, not on the identity of the solute particles. • Among colligative properties are ØVapor pressure lowering ØBoiling point elevation ØMelting point depression ØOsmotic pressure

How many particles? • All covalent molecules have 1 particle – All nonmetals – Sugar – Ethanol • Ionic compounds you must count the # of ions. – Has a metal – Na. Cl=2 particles – Ba. Cl 2 =3 particles

Vapor Pressure As solute molecules are added to a solution, the solvent become less able to evaporate(=decreased vapor pressure).

Boiling Point Elevation and Freezing Point Depression Solute-solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent.

Colligative Properties • Consider three beakers: – 50. 0 g of ice + 0. 15 moles Na. Cl – 50. 0 g of ice + 0. 15 moles sugar (sucrose) • Which will have the lowest freezing point? • Which will have the lowest boiling point?

Colligative Properties - Osmosis • Osmosis: the net movement of a solvent through a semipermeable membrane toward the solution with greater solute concentration. • Movement of solvent from high solvent concentration to low solvent concentration Osmosis plays an important role in living systems: Membranes of red blood cells are semipermeable.