CHEM 135 1st Edition Lecture 5 Outline of Last Lecture I Solutions a Definitions and components b Types of formations II Solubility a Effect of temperature b Effect of pressure III Colligative Properties IV Vapor pressure and Dynamic Equilibrium V Raoult s Law Outline of Current Lecture VI Review of Raoult s Law VII Phase Diagram to indicate Freezing and Boiling point VIII Freezing point depression and boiling point elevation Current Lecture VI Review of Raoult s Law Vapor Pressure of the solution is given by Psolution Xsolvent P solvent Xsolvent mole fraction of the solvent n solvent n solute n solvent Vapor pressure lowering P P Xsolvent P solvent These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Ex Calculate the vapor pressure at 25 C of a solution containing 55 3 g ethylene glycol HOCH2CH2CH2OH and 285 2 g water The vapor pressure of pure water at 25 C is 23 8 torr Psolution Xsolvent P solvent Given P solvent 23 8 torr Mass of solvent 285 2 g Mass of solute 55 3 g Find P solution Strategy mass moles Xsolvent Psolution Xsolvent n solvent n solute n solvent Xsolvent 15 84 mol 0 956 mol 0 727 15 84 Psolution Xsolvent P solvent 0 956 23 8 22 76 torr VII Phase Diagram to indicate Freezing and Boiling point VIII Freezing point depression and boiling point elevation The freezing point of a solution is lower than the freezing point of the pure solvent Tf m Kf The boiling point of a solution is higher than the boiling point of the pure solvent Tb m Kb m molality of a solution in moles solute per kilogram solvent Kf Kb freezing point depression and boiling point elevation constants Ex
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