Presentation on theme: "Solutions Colligative Properties of Solutions. Objectives 1.Describe the colligative properties of a solution. 2.Calculate freezing point depression and."— Presentation transcript:
Solutions Colligative Properties of Solutions
Objectives 1.Describe the colligative properties of a solution. 2.Calculate freezing point depression and boiling point elevation for solutions
Colligative Properties A property that depends on the concentration of solute particles but not on the identity of the solute.
Vapor Pressure Lowering As the concentration of a solute increases, the concentration of the solvent particles at the surface of a liquid decreases. This causes the vapor pressure to be lower. A 1.0 m solution of glucose (C 6 H 12 O 6 ) lowers the vapor pressure to the same extent as a 1.0 m solution of sucrose (C 12 H 22 O 11 )
Freezing Point Depression Freezing Point Depression (Δt f ): the difference between the freezing point of a pure solvent and a solution of a solute in the same solvent. Δt f = K f m K f = molal freezing point constant in o C/m m = molality
Sample Problem 1.What is the freezing point depression of water in a solution of 17.1 g of sucrose (C 12 H 22 O 11 ) and 200. g of water? What is the actual freezing point of water. Water has a Molal F.P. constant of o C/m.
Sample Problem 2.A water solution containing an unknown quantity of a non-electrolyte solute is found to have a freezing point of o C. What is the molal concentration of the solution?
Sample Problems 1.Determine the freezing point of a water solution of fructose (C 6 H 12 O 6 ) made by dissolving 58.0 g of fructose in 185 g of water o C 2.Calculate the molality of a solution of 39.2 g of urea, H 2 NCONH 2, in 485 g of pure acetic acid. Determine the freezing point of this solution. For acetic acid: Normal f.p. = 16.6 o C K f = o C/m 1.35 m, 11.3 o C
Sample Problems 1.What is the expected change in the freezing point of water in a solution of 62.5 g of barium nitrate, Ba(NO 3 ) 2, in 1.00 kg of water.
Sample Problems 1.What is the expected freezing point depression for a solution that contains 2.0 mol of magnesium sulfate dissolved in 1.0 kg of water? -7.4 o C 2.A water solution contains 42.9 g of calcium nitrate dissolved in 500. g of water. Calculate the freezing point of the solution o C
Boiling Point Elevation Boiling Point Elevation (Δt b ): the difference between the boiling point of a pure solvent and a solution of a solute in the same solvent. Δt b = K b m K f = molal boiling point constant in o C/m m = molality
Sample Problem A solution contains 50.0 g of sucrose, C 12 H 22 O 11, a non- electrolyte, dissolved in g of water. What is the boiling point elevation?
Sample Problems 1.What is the boiling point of a solution of 25.0 g of 2-butoxyethanol, HOCH 2 CH 2 OC 4 H 9, in 68.7 g of ether? (For ether, ∆t b = 2.02 o C/m) 40.8 o C 2.What mass of glycerol, CH 2 OHCHOHCH 2 OH, must be dissolved in 1.00 x 10 3 g of water in order to have a boiling point of o C? 810g 3.What is the expected boiling point of a 1.70 m solution of sodium sulfate in water? o C