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)

answer 1m NaCl (aq) only 2 particles ionize 1m C12H22O11(aq) non-electrolyte 1m C2H6O2(aq) non-electrolyte 1m CaCl2(aq) b/c this will ionize into the greatest number (3) of particles CaCl2 Ca2+ + 2Cl-

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

answer 2m NaCl (aq) BECAUSE 2m NaCl (aq) ionizes into 2 particles x 2m = 4m concentration of particles in solution 1m C12H22O11(aq) doesn’t ionize (non-electrolyte) = 1m concentration of particles in solution 1.5m C2H6O2(aq) doesn’t ionize = 1.5m concentration of particles in solution 1m CaCl2(aq) ionizes (electrolyte) into 3 particles, but only 1m concentration = 3m concentration of particles in solution

Different solvents have different Kf & Kb ∆Tb = Kb m ∆Tf = Kf m We could calculate the actual freezing point and boiling point, but we’ll save that for another time.

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