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Colligative Properties Or Properties of Solutions

Did you ever wonder how the antifreeze in your car can both protect your engine from overheating and keep it from freezing?. Colligative Properties Or Properties of Solutions

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Colligative Properties Or Properties of Solutions

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  1. Did you ever wonder how the antifreeze in your car can both protect your engine from overheating and keep it from freezing?

  2. Colligative Properties Or Properties of Solutions When you put stuff into solution, the molecules of solute get in the way of the molecules of solvent. This makes certain things difficult for the solution, compared to pure solvent.

  3. For example, there is less room at the surface of the solution. This leaves fewer opportunities for molecules of solvent to vaporize. Therefore, the vapor pressure is reduced.

  4. Colligative property #1: Vapor pressure decreases

  5. What effect would that have on boiling point? Would it make it easier or harder to get the liquid to boil? Would it boil at a higher or lower temperature? Ever wonder why you are supposed to add salt to the water when cooking pasta?

  6. Colligative property #2: Boiling point increases

  7. The amount of change in the boiling point (ΔTb) depends on the concentration of particles in solution (molality, m) and the identity of the solvent (not the solute).

  8. Each solvent is effected somewhat differently, yet the effect is consistent for that solvent regardless of what solute is used. Therefore, each solvent has it's own Boiling Point Elevation Constant (Kb) which can be looked up on tables. ∆T≈Kbm

  9. ΔTb = iKbm But Mrs. Dempsey, what's this i thing in our notes?! I'm so glad you asked... Molality reflects how many moles of stuff you put in, “i” accounts for disassociation. ΔTb = iKbm

  10. In solution, how many particles does NaCl disassociate into? i = C6H12O6? i = Mg(NO3)2?i =

  11. Molecules of solvent also interfere with freezing by disrupting the solvent's molecular framework. Molecules in a solid need to bond tightly, right? Solute gets in the way of that.

  12. Would that make it easier or harder for a substance to freeze? What effect would that have on the temperature at which a substance freezes?

  13. Colligative property #3: Freezing point decreases I know you can think of an example of this...

  14. The equation is the same, except that the “bs” become “fs”: ΔTf= iKf m

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