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Solutions

Solutions. Part 4. Colligative Properties. Physical properties of solutions that are affected by the number of particles, not the identity of the particles. Include: Vapor pressure lowering Boiling point elevation Freezing point depression. Electrolytes. NaCl  Na + + Cl -

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Solutions

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  1. Solutions Part 4

  2. Colligative Properties • Physical properties of solutions that are affected by the number of particles, not the identity of the particles. • Include: • Vapor pressure lowering • Boiling point elevation • Freezing point depression

  3. Electrolytes NaCl  Na+ + Cl- • When sodium chloride is dissolved in water, the compound dissociates almost completely into ions • A 1m solution of NaCl produces 2m of ions • Solutions with electrolytes conduct electricity

  4. Practice • How many ions do each of the following dissociate into? • MgCl2 • Ca(OH)2 • Fe3(PO4)2 • C6H12O6

  5. Non-Electrolytes • Solutions with non-electrolytes do not conduct electricity • Non-electrolytes dissolve, but do not ionize • Colligative properties depend on the number of particles in solution

  6. Vapor Pressure Lowering • Vapor pressure is the result of atoms at the surface evaporating and exerting pressure on the surface • Solutes interfere with this process, thus lowering the vapor pressure • The greater the number of particles of solute, the lower the vapor pressure

  7. Boiling Point Elevation • Because the vapor pressure has been lowered, it takes more kinetic energy to boil the solution compared to the pure solvent • BPE is the difference in boiling point temperature ΔTb = Kbm Kb – boiling point elevation constant

  8. Boiling Point Elevation • What is the boiling point elevation of a 0.029m NaCl solution? (Kb of water = 0.512 °C/m)

  9. Freezing Point Depression • The solute particles interfere with the ability of the solvent to form a solid. • The freezing point of a solution is lower than the freezing point of a solvent. ΔTf = Kfm

  10. Freezing Point Depression • What is the freezing point depression of a 0.029m MgCl2 solution? (Kf of water = 1.86 °C/m)

  11. Freezing Point Depression • Which would be more effective to use to prevent roads from icing over, NaCl or MgCl2?

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