116-collig - Chem 116 Colligative Properties 8/29/2011...

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Chem 116 Colligative Properties 8/29/2011 1 1. 2. 3. 4. Knowledge of colligative properties explains why/how: sprinkle salt on roads in winter, add antifreeze to radiator, use deicer on airplane wings, can obtain freshwater from seawater (desalination), refining of petroleum, etc. The FOUR Colligative properties are… Colligative Properties Properties of a solution that depend on the number/amount of solute particles dissolved in solution (amount), and not on the chemical identity of the solute. Note: Number of dissolved solute particles in solution, depend on whether the solute is a strong, weak, or non-electrolyte!!! Vapor Pressure Lowering CASE #1: Nonvolatile solute dissolved in solvent. Vapor Pressure: VP (pure solvent) > VP (solution) add sugar pure solvent solution Raoult’s Law Vapor pressure of a solution is dependent on how much (i.e. conc.) SOLVENT is present!! Raoult’s Law works best for ideal solutions: 1. 2. Derive the expression for the change in Vapor Pressure ( Δ P). solvent pure of pressure vapor solvent the of fraction mole solution the of pressure vapor ln soln = = = = o solvent solvent so o solv solv P X P P X P 1. Calculate the vapor pressure of a solution made by dissolving 20.0 g glucose, C 6 H 12 O 6 , in 500.0 g of water. The vapor pressure of pure water is 47.1 torr at 37 ° C. 2. What is the vapor pressure (in mm Hg) of a solution made by dissolving 5.0 g of CaCl 2 in 50.0 g of H 2 O at 70 ºC. The vapor pressure of pure water at 70 ºC is 233.7 mm Hg. 3. How many grams of sucrose must be added to 320. g of water to lower the vapor pressure by 1.5 mm Hg at 25 ºC? The vapor pressure of water at 25 ºC is 23.8 mm Hg, and the molar mass of sucrose is 342.3 g/mol. (4.1 x10 2 g)
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Chem 116 Colligative Properties 8/29/2011 2 Vapor Pressure Lowering CASE #2: Two (or more) volatile substances mixed. Both substances contribute to VP of
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116-collig - Chem 116 Colligative Properties 8/29/2011...

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