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# Vapor Pressure Lowering (Raoult's Law)

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Sections
Solutions: Solubility and Intermolecular Forces
Molality
Parts per Million (ppm)
Mole Fraction
Solutions: Mass Percent
Types of Aqueous Solutions
Intro to Henry's Law
Henry's Law Calculations
The Colligative Properties
Boiling Point Elevation
Freezing Point Depression
Osmosis
Osmotic Pressure
Vapor Pressure Lowering (Raoult's Law)
The Freezing Point Depression (IGNORE)

Vapor Pressure is the pressure exerted by a gas at equilibrium with its liquid phase at a specific temperature in a closed system.

###### Understanding Raoult's Law & Vapor Pressure Lowering

Concept #1: Vapor Pressure Lowering

Example #1: Calculate the vapor pressure (in torr) of a solution containing 53.7 g Cd(NO3)2 (MW: 236.43 g/mol) in 155 g of water at 30.0ºC. The vapor pressure of pure water at this temperature is 131.8 torr.

Practice: How many grams of glucose, C6H12O6, must be added to 515.0 g of water to give a solution with a vapor pressure of 13.2 torr at 20.0ºC? The vapor pressure of pure water at 20.0ºC is 17.5 torr.

Practice: Determine the vapor pressure lowering associated with 1.32 m C6H12O6 solution (MW: 180.156 g/mol) at 25°C. The vapor pressure of pure water at 25°C is 23.8 torr.

Practice: The vapor pressure of water at 100.0ºC is 0.720 atm. Determine the mass percent of iron (II) chloride, FeCl2, needed to reduce its vapor pressure to 0.655 atm. (MW of FeCl2 is 126.756 g/mol)