17. Benzene, C.He, and toluene, CH-CH, form ideal solutions. At 35°C the vapor pressure of benzene is 160. torr and that of toluene is 50.0 torr. In an experiment, 3.9 mol of benzene and 4.9 mol of toluene are placed in a closed container at 35°C and allowed to come to equilibrium. What is the mole fraction of toluene in the vapor phase? a) 0.15 b) 0.28 c) 0.52 d) 0.60 e) 0.72 a) b) c) 18. Which of the following methods cannot be used to determine the molar mass of a nonelectrolyte? measurement of the freezing-point depression of a solution of the compound measurement of the boiling-point elevation of a solution of the compound measurement of the osmotic pressure of a solution of the compound d) measurement of the x-ray diffraction of a pure crystal of the compound e) measurement of the pressure, temperature, volume, and mass of the compound in the gaseous state a) 1,1 b) 2,1 c) 1,2 d) 4,1 e) 1,4 19. As the number of solute particles in a given volume of solution increases, a) b) the freezing point will increase and the vapor pressure will increase. the freezing point will decrease and the vapor pressure will decrease. the boiling point will increase and the vapor pressure will increase. the boiling point will decrease and the vapor pressure will decrease. the osmotic pressure will decrease and the lattice energy will increase. The volume of a 15.6% (by mass) solution is 79.2 mL. The density of the solution is 1.480 g/mL. What is the mass of the solution? c) d) e) 20. a) 183 g b) 53.5 g c) d) e) 18.3 g 117 g 1830 g 21. For a solution containing only one solute dissolved in a solvent, we can calculate the mole fraction of the solvent directly, given only a) the density of the solution. b) the molarity of the solution. c) the mole fraction of the solute. d) the molar mass of the solvent. e) the molar mass of the solute. 22. 23. 23 What is the molar mass of an aromatic hydrocarbon if 0.71 g of the compound depresses the freezing point of 125 g of benzene by 0.26°C? (Ky for benzene is 5.12°C/m.) What is the freezing point of an aqueous 1.18 m CaCl2 solution? (Ky for water is 1.858°C/m.)