5 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 (C6H12O6) lowers the vapor pressure to the same extent as a 1.0 m solution of sucrose (C12H22O11)
7 Freezing Point Depression Freezing Point Depression (Δtf): the difference between the freezing point of a pure solvent and a solution of a solute in the same solvent.Δtf = KfmKf = molal freezing point constant in oC/mm = molality
8 Sample ProblemWhat is the freezing point depression of water in a solution of 17.1 g of sucrose (C12H22O11) and 200. g of water? What is the actual freezing point of water. Water has a Molal F.P. constant of oC/m.
9 Sample ProblemA water solution containing an unknown quantity of a non-electrolyte solute is found to have a freezing point of oC. What is the molal concentration of the solution?
10 Sample ProblemsDetermine the freezing point of a water solution of fructose (C6H12O6) made by dissolving 58.0 g of fructose in 185 g of water.-3.24oCCalculate the molality of a solution of 39.2 g of urea, H2NCONH2, in 485 g of pure acetic acid. Determine the freezing point of this solution.For acetic acid:Normal f.p. = 16.6oCKf = oC/m1.35 m, 11.3 oC
11 Sample ProblemsWhat is the expected change in the freezing point of water in a solution of 62.5 g of barium nitrate, Ba(NO3)2, in 1.00 kg of water.
12 Sample ProblemsWhat is the expected freezing point depression for a solution that contains 2.0 mol of magnesium sulfate dissolved in 1.0 kg of water?-7.4oCA water solution contains 42.9 g of calcium nitrate dissolved in 500. g of water. Calculate the freezing point of the solution.-2.92oC
13 Boiling Point Elevation Boiling Point Elevation (Δtb): the difference between the boiling point of a pure solvent and a solution of a solute in the same solvent.Δtb = KbmKf = molal boiling point constant in oC/mm = molality
14 Sample ProblemA solution contains 50.0 g of sucrose, C12H22O11, a non-electrolyte, dissolved in g of water. What is the boiling point elevation?
15 Sample ProblemsWhat is the boiling point of a solution of 25.0 g of 2-butoxyethanol, HOCH2CH2OC4H9, in 68.7 g of ether? (For ether, ∆tb= 2.02oC/m)40.8oCWhat mass of glycerol, CH2OHCHOHCH2OH, must be dissolved in 1.00 x 103 g of water in order to have a boiling point of 104.5oC?810gWhat is the expected boiling point of a 1.70 m solution of sodium sulfate in water?102.6oC