PSU CHEM 110 - Colligative Properties

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Colligative PropertiesColligative PropertiesColligative?Number of Solute ParticlesPractice ProblemVapor Pressure LoweringPractice ProblemPhase Diagrams for SolutionsBoiling Point ElevationFreezing Point DepressionFreezing Point Depression and Ocean WaterDaniel FahrenheitDaniel FahrenheitMolecular Weight DeterminationOsmosisConsequences of Osmotic PressureWhat You Should KnowColligative PropertiesCH110 FA11 SAS 1Exam 3: Monday November 7thPrepare for Recitation November 10thALEKS Objective 11 due November 5thANGEL Quiz 11, November 6thNote the special due dates!Lecture 31: November 2ndLecture 32: November 4thLecture 33: November 7th(Review for Exam)Read: Ch. 13.5,13.6Additional Preparation: BLB 13: 9,58,61,69,75; Packet 13: 13-18CH110 FA11 SAS 2By the end of Today’s Lecture you should know:Vapor pressure loweringBoiling point elevationFreezing point depressionOsmotic pressureKEY QUESTIONS: THE BIG PICTUREColligative PropertiesHow do you determine the total solute concentration in a solution?What forces drive the dissolution process?How do the properties of solutions differ from the properties of pure solvents?Remember: macroscopic properties come from microscopic originsHow does the change in vapor pressure as a function of solute concentration influence the freezing and boiling points of solutions?What is the relationship between vapor pressure and osmotic pressure?Colligative?CH110 FA11 SAS 3What determines Colligative Properties?1) 2) Colligative Properties Affect:• Vapor pressure (Lowering)• Boiling point (Elevation)• Freezing point (Depression)• Osmotic pressure (next time…)Colligative:Number of Solute ParticlesCH110 FA11 SAS 4How many particles are in solution?0.5 m (molal) solution of Pb(NO3)2Is it an electrolyte?Concentration of Pb2+Concentration of NO3-Total m of particles = 0.5 m (molal) solution of CH3COOHIs it an electrolyte? Total CH3COOH and CH3COO-Concentration of H+ Total m of particles =Practice ProblemCH110 FA11 SAS 5Which of the following has the highest molality of particles?A) 0.2 m aluminum sulfateB) 0.3 m ammonium sulfateC) 0.4 m potassium hydroxideD) 0.2 m sugarE) 0.3 m acetic acidVapor Pressure LoweringCH110 FA11 SAS 6• The lowering of vapor pressure is a colligative property• Depends upon _____________ of non-volatile solute particles, not their _______• Favorable solute-solvent interactions require more kinetic energy to overcome:Raoult’s LawAddition of a non-volatile solute to a solvent lowers the vapor pressurePA= vapor pressure of solutionXA= mole fraction of solventPoA= vapor pressure of pure solventPractice ProblemCH110 FA11 SAS 7The vapor pressure of water is 23.76 torr at 25oC. What is the vapor pressure of an aqueous soln. at 25oC made by dissolving 84.75 g C11H22O11in 100.0 g of H2O?A. 21.7 torrB. 22.7 torrC. 23.76 torrD. 24.9 torrE. 25.9 torrPhase Diagrams for SolutionsCH110 FA11 SAS 8How is melting point affected by the solute particles?How is boiling point affected by the solute particles?Boiling Point ElevationCH110 FA11 SAS 9• Boiling point :• Colligative properties _________ vapor pressure, so a ______ temperature is required to reach boiling than for pure solventAddition of a non-volatile solute to a solvent increases the boiling pointKB= molal boiling point elevation constantm = total molality of soluteKBdepends on solvent:KB(water) = 0.51 oC m-1Freezing Point DepressionCH110 FA11 SAS 10Addition of a non-volatile solute to a solvent decreases the freezing point• Colligative properties decrease the freezing point of solutions compared to pure solvent• The triple point of the phase diagram must be at a lower temperature. Why? KF= molal f.p. depression constantm = total molality of soluteKFdepends on solvent:KF(water) = 1.86 oC m-1Freezing Point Depressionand Ocean WaterCH110 FA11 SAS 11Ocean water is full of solute particles: e.g., Cl-, SO42-, Mg2+, Na+, Ca2+, K+ but mostly NaCl ( ~ 35 g / 1 kg water). What is the freezing point of ocean water?A. -2.23 oCB. -1.12 oCC. 0.0 oCD. 1.12 oCE. 2.23 oCDaniel FahrenheitCH110 FA11 SAS 12Fahrenheit created a saturated NH4Cl solution called a “Frigorific Mixture” (a solution that stabilizes at a fixed temperature). The mixture was 20.4% NH4Cl by weight. What was the freezing point of the mixture?Fahrenheit’s ScaleDaniel FahrenheitCH110 FA11 SAS 13• Temperature scales are defined by twopoints (needed to define a line)• Fahrenheit’s wife’s oral temperature was originally defined as 100oF. • Ultimately, the definition of 100oF was re-standardized to the rectal temperature of a cow.• Only Americans still use this system.Molecular Weight DeterminationCH110 FA11 SAS 14Stepwise Problem Solving1. From ΔTbor ΔTfcalculate m from solution (molality)2. From m and knowledge of how the solution was prepared, calculate MWExampleA solution of 12 g of glucose in 100 g H2O boils at 100.340oC. What is the MW of glucose? (Kbwater = 0.51 oC m-1)OsmosisCH110 FA11 SAS 15concentratedsolutionsemipermeablemembrane• movement continues until osmotic pressurebuilds up to stop itOsmosis: the net movement of _______toward the solution with _________ solute concentration.Osmotic Pressure:pure solvent-or-dilutesolutionConsequences of Osmotic PressureCH110 FA11 SAS 16• Red Blood Cells have a semi-permeable membrane.• The solute concentration in blood plasma is regulatedcell in hypertonicsolution(mcell< mplama)cell in hypotonicsolution(mcell> mplama)What You Should Know CH110 FA11 SAS 17Colligative Properties and Vapor Pressure• What are colligative properties and what do they depend on?• What is the relationship between solute concentration and the vapor pressure of a solvent?Freezing point and Boiling Point• Why does addition of a solute to a solvent decrease its freezing point?• Why does addition of a solute to a solvent increase its boiling point?• How can we use these properties to determine solute molecular weights?Osmotic Pressure• What is osmotic pressure?• What are hypertonic and hypotonic


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PSU CHEM 110 - Colligative Properties

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