Colligative Properties Physical properties (melting point and boiling point) of solutions depend on the concentration of solute particles in solution

Freezing point depression When a solute is dissolved in a liquid the freezing point of the solution will be lower ↓ than the pure liquid. The freezing point of water is less than 0oC if something is dissolved in it.

Boiling point Elevation When a solute is dissolved in a liquid the boiling point of the solution will be higher ↑ than the pure liquid. The boiling point of water is more than 100oC if something is dissolved in it.

1m electrolyte vs. 1m non-electrolyte How much ΔT changes depends on Concentration of SOLUTE PARTICLES in sol’n 1m electrolyte vs. 1m non-electrolyte 1m NaCl vs. 2m NaCl 1m NaCl vs. 2m C12H22O11

Which would result in the lowest freezing point / highest boiling point? 1m NaCl (aq) 1m C12H22O11(aq) 1m C2H6O2(aq) 1m CaCl2(aq)

Which would result in the lowest freezing point / highest boiling point? 2m NaCl (aq) 1m C12H22O11(aq) 1.5m C2H6O2(aq) 1m CaCl2(aq)

Different solvents have different Kf & Kb

Formulae ∆Tb = Kb m ∆Tf = Kf m Delta T = change in freezing point temperature (or boiling point temp) Kb or Kf is Konstant molality = mol of solute per Kg of solvent

Practice problem I add 25.0g of NaCl to 100.0g of water. BP = 105.65oC What is the new boiling point? What is the new freezing point? BP = 105.65oC FP = -20.3oC

Practice problem #2 Benzene has a boiling point of 80.1oC, when 6.2g of an unknown substance is added to 150.0g of benzene, its boiling point increases to 85.2oC. What is the molar mass of the unknown substance? 20.5 g/mol

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