Colligative Properties Prepare for Recitation November 10th ALEKS Objective 11 due November 5th ANGEL Quiz 11 November 6th Note the special due dates Lecture 31 November 2nd Lecture 32 November 4th Lecture 33 November 7th Review for Exam Read Ch 13 5 13 6 Additional Preparation BLB 13 9 58 61 69 75 Packet 13 13 18 Exam 3 Monday November 7th CH110 FA11 SAS 1 Colligative Properties KEY QUESTIONS THE BIG PICTURE How 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 origins How 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 By the end of Today s Lecture you should know Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure CH110 FA11 SAS 2 Colligative Colligative What determines Colligative Properties 1 2 Colligative Properties Affect Vapor pressure Lowering Boiling point Elevation Freezing point Depression Osmotic pressure next time CH110 FA11 SAS 3 Number of Solute Particles How many particles are in solution 0 5 m molal solution of Pb NO3 2 Is it an electrolyte Concentration of Pb2 Concentration of NO3Total m of particles 0 5 m molal solution of CH3COOH Is it an electrolyte Total CH3COOH and CH3COOConcentration of H Total m of particles CH110 FA11 SAS 4 Practice Problem Which of the following has the highest molality of particles A B C D E 0 2 m aluminum sulfate 0 3 m ammonium sulfate 0 4 m potassium hydroxide 0 2 m sugar 0 3 m acetic acid CH110 FA11 SAS 5 Vapor Pressure Lowering Addition of a non volatile solute to a solvent lowers the vapor pressure The lowering of vapor pressure is a colligative property Depends upon of nonvolatile solute particles not their Favorable solute solvent interactions require more kinetic energy to overcome Raoult s Law PA vapor pressure of solution XA mole fraction of solvent PoA vapor pressure of pure solvent CH110 FA11 SAS 6 Practice Problem The 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 C11H22O11 in 100 0 g of H2O A B C D E 21 7 torr 22 7 torr 23 76 torr 24 9 torr 25 9 torr CH110 FA11 SAS 7 Phase Diagrams for Solutions How is melting point affected by the solute particles How is boiling point affected by the solute particles CH110 FA11 SAS 8 Boiling Point Elevation Addition of a non volatile solute to a solvent increases the boiling point Boiling point Colligative properties vapor pressure so a temperature is required to reach boiling than for pure solvent KB molal boiling point elevation constant m total molality of solute KB depends on solvent KB water 0 51 oC m 1 CH110 FA11 SAS 9 Freezing Point Depression Addition 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 constant m total molality of solute KF depends on solvent KF water 1 86 oC m 1 CH110 FA11 SAS 10 Freezing Point Depression and Ocean Water Ocean 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 B C D E 2 23 oC 1 12 oC 0 0 oC 1 12 oC 2 23 oC CH110 FA11 SAS 11 Daniel Fahrenheit Fahrenheit 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 Scale CH110 FA11 SAS 12 Daniel Fahrenheit Temperature scales are defined by two points needed to define a line Fahrenheit s wife s oral temperature was originally defined as 100oF Ultimately the definition of 100oF was restandardized to the rectal temperature of a cow Only Americans still use this system CH110 FA11 SAS 13 Molecular Weight Determination Stepwise Problem Solving 1 From Tb or Tf calculate m from solution molality 2 From m and knowledge of how the solution was prepared calculate MW Example A solution of 12 g of glucose in 100 g H2O boils at 100 340oC What is the MW of glucose Kb water 0 51 oC m 1 CH110 FA11 SAS 14 Osmosis pure solvent ordilute solution concentrated solution semipermeable membrane Osmosis the net movement of toward the solution with solute concentration movement continues until osmotic pressure builds up to stop it Osmotic Pressure CH110 FA11 SAS 15 Consequences of Osmotic Pressure Red Blood Cells have a semi permeable membrane The solute concentration in blood plasma is regulated cell in hypertonic solution mcell mplama cell in hypotonic solution mcell mplama CH110 FA11 SAS 16 What You Should Know Colligative 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 solutions CH110 FA11 SAS 17
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