Colligative Prperties Oklahoma City Community College依数性质俄克拉荷马城社区学院.pptVIP

Colligative Properties Consider three beakers: 50.0 g of ice 50.0 g of ice + 0.15 moles NaCl 50.0 g of ice + 0.15 moles sugar (sucrose) What will the temperature of each beaker be? Beaker 1: Beaker 2: Beaker 3: Colligative Properties The reduction of the freezing point of a substance is an example of a colligative property: A property of a solvent that depends on the total number of solute particles present There are four colligative properties to consider: Vapor pressure lowering (Raoult’s Law) Freezing point depression Boiling point elevation Osmotic pressure Colligative Properties – Vapor Pressure A solvent in a closed container reaches a state of dynamic equilibrium. The pressure exerted by the vapor in the headspace is referred to as the vapor pressure of the solvent. The addition of any nonvolatile solute (one with no measurable vapor pressure) to any solvent reduces the vapor pressure of the solvent. Colligative Properties – Vapor Pressure Nonvolatile solutes reduce the ability of the surface solvent molecules to escape the liquid. Vapor pressure is lowered. The extent of vapor pressure lowering depends on the amount of solute. Raoult’s Law quantifies the amount of vapor pressure lowering observed. Colligative Properties – Vapor Pressure Raoult’s Law: PA = XAPOA where PA = partial pressure of the solvent vapor above the solution (ie with the solute) XA = mole fraction of the solvent PoA = vapor pressure of the pure solvent Colligative Properties – Vapor Pressure Example: The vapor pressure of water at 20oC is 17.5 torr. Calculate the vapor pressure of an aqueous solution prepared by adding 36.0 g of glucose (C6H12O6) to 14.4 g of water. Colligative Properties – Vapor Pressure Solution: Answer: 14.0 torr Colligative Properties – Vapor Pressure Example: The vapor pressure of pure water at 110oC is 1070 torr. A solution of ethylene glycol and water has a vapor pressure of 1.10 atm at the same temperature. What is the mol