Chem_215_Lect_37_Color

# Chem_215_Lect_37_Color - Vapor Pressure of Pure Liquid vs...

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1 Vapor Pressure of Pure Liquid vs. Solution The vapor pressure of a liquid when pure is greater than when it is in a solution.

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2 Vapor Pressures of Solutions Raoult’s Law: The partial pressure of a solvent vapor above an ideal solution P A is given by P A = X A P o A X A = mole fraction of solvent in solution P o A = vapor pressure of pure solvent Consider NaCl (aq). At 25 o C, the vapor pressure of water is 23 Torr (23 mm Hg). Plot the vapor pressure of the solution as a function of mole fraction water. pure NaCl X H2O pure H 2 O Add 0.1 mol NaCl to 0.9 mol of H 2 O. NaCl (s) Na + (aq) + Cl - (aq) 82 . 0 1 . 1 9 . 0 1 . 0 1 . 0 9 . 0 9 . 0 Cl moles Na moles O H moles O H moles moles total O H moles X 2 2 2 O 2 H = = + + = + + = = + Torr 9 . 18 ) Torr 23 )( 82 . 0 ( P X P o O 2 H O 2 H O 2 H = = =