userdata-paziras-Chem101-Chap_12A

204 06 08 molefractionofsolventa 10xa pao pa

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Unformatted text preview: ne Glyco l can be considered to be nonvo lat ile compared to Water · The Vapor pressure of a volatile solvent is lowered by addition of a nonvolatile solute. Pure Solvent (water) Pv at 20°C Solution (0.100 mole fract ion ethylene glyco l in water) 17.54 mmHg 17.36 mmHg DP = Vapor Pressure Lowering = 17.54 mm Hg – 17.36 mm Hg = 0.18 mm Hg Raoult’s Observat ion; · The Vapor Pressure of a solvent (A) over the solut ion of a non­electrolyte so lute (B) depends on the Mole Fract ion (XA) of so lvent in the solut ion. SOLUTION = SOLVENT A + (volat ile) SOLUTE B (non­electrolyte) (volat ile or nonvo lat ile) 13 Chemistry 101 Chapter 12 RAOULT’S LAW · The partial pressure of so lvent (PA) over a solution equals the vapor pressure of the pure solvent (PA o) times the mo le fraction of so lvent A in the so lut ion (XA) PA = PAo x XA partial pressure of solvent A over a solut ion (A+B) NOTE: (1) XA < 1 (2) vapor pressure of pure solvent A mo les A XA = ¾¾¾¾¾¾¾ mo les A + mo les B PA< PA o ; Vapor Pressure is lowered therefore: If so lute B is nonvo lat ile: PA = PT (Total vapor pressure of so lution) IDEAL SOLUTIONS: · These are so lut ions for which Raoult’s Law ho lds true for ALL VALUES OF MOLE FRACTIONS. · In these so lutions: Ø Solvent A and Solute B are chemically similar Ø Intermo lecular Forces of Attraction between: A ¾> <¾ B similar to A ¾> <¾ A similar to Ø Solvent A is vo lat ile Ø Solute B is a non­electrolyte and may be vo lat ile or nonvo lat ile NON­IDEAL SOLUTIONS: · These are so lut ions for which Raoult’s Law ho lds true only if : Ø Solute B is a nonvo latile electrolyte and Ø Solution is dilute (XA >>>>> XB) 14 B ¾> <¾ B Chemistry 101 Chapter 12 IDEAL & NON­IDEAL SOLUTIONS PAo PA (Vapor Pressure of Pure Solvent A) (mm Hg) IDEAL SOLUTION Concentration of solution increases 0.2 0.4 0.6 0.8 (Mole Fraction of Solvent A) 1.0 XA PAo PA (Vapor Pressure of Pure Solvent A) (mm Hg) NON­IDEAL SOLUTION (follows Raoult’s law for dilute solution) Concentration of solution increases 0.2 0.4 0.6 0.8 (Mole Fraction of Solvent A) 15 1.0 XA Chemistry 101 Chapter 12 For an Ideal Solut ion: DP = Vapor Pressure Lowering DP = PA o ­ PA = PA o - PA o XA = PA o (1 - XA) Recall: Mole Fract ion of Component 1 + Mole Fract ion of Component 2 = 1 Mole Frac...
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This document was uploaded on 03/18/2014 for the course CHEM 101 at Los Angeles Mission College.

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