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Colligative Properties of Solutions

Colligative Properties of Solutions. Chemistry Mrs. Coyle. How do you get from this… . …to this?. Add an ionic compound!. Colligative Properties. Properties that depend only on the number of solute particles and not on their identity. Some Colligative Properties are:.

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Colligative Properties of Solutions

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  1. Colligative Properties of Solutions Chemistry Mrs. Coyle

  2. How do you get from this…

  3. …to this?

  4. Add an ionic compound!

  5. Colligative Properties • Properties that depend only on the number of solute particles and not on their identity.

  6. Some Colligative Properties are: • Vapor pressure lowering • Boiling point elevation • Freezing Point depression

  7. Vapor Pressure

  8. Vapor Pressure Lowering • The particles of solute are surrounded by and attracted to particles of solvent. • Now the solvent particles have less kinetic energy and tend less to escape into the space above the liquid. • So the vapor pressure is less.

  9. Ionic vs Molecular Solutes • Ionic solutes produce two or more ion particles in solution. • They affect the colligative properties proportionately more than molecular solutes (that do not ionize). • The effect is proportional to the number of particles of the solute in the solution.

  10. How many particles do each of the following give upon solvation? • NaCl • CaCl2 • Glucose

  11. Freezing Point Depression

  12. Example • Salt is added to melt ice by reducing the freezing point of water.

  13. Boiling Point Elevation

  14. Example • Addition of ethylene glycol C2H6O2 (antifreeze) to car radiators.

  15. Freezing Point Depression and Boiling Point Elevation Boiling Point Elevation • ∆Tb =mkb (for water kb=0.51 oC/m) • Freezing Point Depression • ∆Tf=mkf (for water kf=1.86 oC/m) • Note: m is the molality of the particles, so if the solute is ionic, multiply by the #of particles it dissociates to.

  16. Which is more effective for lowering the freezing point of water? • NaCl or CaCl2

  17. Example 1: • Find the new freezing point of 3m NaCl in water.

  18. Example 2: • Find the new boiling point of 3m NaCl in water.

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