colligative properties of solutions chemistry mrs. coyle
TRANSCRIPT
![Page 1: Colligative Properties of Solutions Chemistry Mrs. Coyle](https://reader036.vdocument.in/reader036/viewer/2022082404/56649dd25503460f94ac914e/html5/thumbnails/1.jpg)
Colligative Properties of Solutions
Chemistry
Mrs. Coyle
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How do you get from this…
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…to this?
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Add an ionic compound!
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Colligative Properties
• Properties that depend only on the number of solute particles and not on their identity.
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Some Colligative Properties are:
• Vapor pressure lowering
• Boiling point elevation
• Freezing Point depression
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Vapor Pressure
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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.
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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.
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How many particles do each of the following give upon solvation?
• NaCl
• CaCl2• Glucose
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Freezing Point Depression
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Example
• Salt is added to melt ice by reducing the freezing point of water.
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Boiling Point Elevation
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Example• Addition of ethylene glycol C2H6O2
(antifreeze) to car radiators.
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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.
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Which is more effective for lowering the freezing point of water?
• NaCl or CaCl2
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Example 1:
• Find the new freezing point of 3m NaCl in water.
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Example 2:
• Find the new boiling point of 3m NaCl in water.