9 - Colligative Properties

9 - Colligative Properties - Colligative Properties...

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Click to edit Master subtitle style Colligative Properties Practical uses of solutions
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Colligative Property A colligative property is a property that depends  ONLY on the amount of the substance present  NOT on the identity of the substance. In other words, it doesn’t matter if it is salt, sugar,  gasoline, or tennis balls – it will behave the same  way!
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Some Examples: p Vapor Pressure Reduction § Related to boiling point p Freezing Point Depression § Salt on the road § Anti-freeze in your radiator p Boiling Point Elevation § Anti-freeze in your radiator p Osmotic Pressure
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Vapor Pressure Reduction What is “vapor pressure”? Vapor pressure is the amount (P   n for ideal  gases) of gas A that is in equilibrium above the  surface of liquid A.
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Vapor Pressure  Surface of liquid At equilibrium, the rate of evaporation (liquid to gas) equals the rate of condensation (gas to liquid). The amount of gas is the “vapor pressure”
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What if you add a solute?  Surface of liquid At equilibrium, the rate of evaporation still must equal the rate of condensation. But at any given temperature, the # of solvent molecules at the surface is decreased and, therefore, so is the vapor pressure
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Boiling Point Elevation What is the “boiling point” of a liquid? It is the temperature at which the vapor pressure equals the  atmospheric pressure.  So… …if you decrease the vapor pressure, you must increase  the boiling point – it will take a higher temperature to get  enough gas molecules (vapor pressure) to equal the  atmospheric pressure.
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Boiling Pt. Elevation
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9 - Colligative Properties - Colligative Properties...

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