CHM1046 LECTURE NOTES 12 7 Colligative Properties dependent upon quantity include boiling point elevation Freezing point depression and Osmotic pressure 1 Boiling pt elevation Tb change in boiling pt Tb m kb Higher molality more solute you have the larger Tb will be Tb Tb solution Tb pure solvent Larger Tb means boiling pt of solution is greater than boiling pt of pure solvent example salt water has a higher Tb than just water The more solute present the higher the boiling pt of the solution 2 Freezing pt depression Tf Tf Tf solution Tf solvent Tf m kf solvent 3 Osmotic pressure Higher molality means larger Tf The freezing pt of solution is lower than that of pure Osmosis the movement of solvent molecules from a less concentrated medium to a more concentrated medium through a semipermeable membrane Osmotic pressure pressure required to stop the flow of the solvent molecules M R T M molarity R gas constant which is 0 08206 L atm mol K and T temperature K In ionic solutions the of ions should be considered using Vant Hoff factor i i moles of particles in solution moles of formula unites dissolved In ionic solutions Tf i m kf T b i m kb i M R T
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