Exam 1-solutions - Version 026 Exam 1 fakhreddine (51615) 1...

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Unformatted text preview: Version 026 Exam 1 fakhreddine (51615) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Kb for benzene is 2.53 C/m and Kf for ben- zene is 5.12 C/m The freezing point of a benzene solution is 2 C. What is the expected normal boiling point of the solution? The normal freezing point of benzene is 5 . 5 C and the normal boiling point of benzene is 80 . 1 C. 1. 83.24 C 2. 81.83 C correct 3. 80.20 C 4. None of these 5. 78.06 C 6. 79.32 C Explanation: T 1 = 2 C k f = 5 . 12 K mol / kg T 2 = 5 . 5 C k b = 5 . 12 K mol / kg T f = 5 . 5 C- 2 C = 3 . 5 K = k f m m = T f k f = 3 . 5 K 5 . 12 K mol / kg = 0 . 683594 mol / kg . The change in boiling point temperature is T b = k b m = 2 . 53 K mol / kg (0 . 683594 mol / kg) = 1 . 72949 K = 1 . 72949 C . and the boiling point is BP = 80 . 1 C + 1 . 72949 C = 81 . 8295 C . 002 10.0 points Which one of the following statements is false? 1. Carbon tetrachloride (CCl 4 ) is more mis- cible with hexane (C 6 H 14 ) than it is with a polar solvent such as methanol (CH 3 OH). 2. Gases are generally more soluble in water at high temperatures than at low tempera- tures. correct 3. As temperature increases, the solubilities of some solids in liquids increase and the sol- ubilities of other solids in liquids decrease. 4. Gases are generally more soluble in water under high pressures than under low pres- sures. 5. Water dissolves many ionic solutes be- cause of its ability to hydrate ions in solu- tion. Explanation: The polarity of water allows it to hydrate the individual ions in the ionic solute. CCl 4 is non-polar and will be miscible with another non-polar liquid and not with a polar one. Increasing temperature makes salts with exothermic H sol more soluble, but salts with endothermic H sol less soluble. Gases are generally more soluble in water under high pressures than under low pressures because of Henrys Law; as the pressure of a gas above a liquid increases, the concentration of the gas in the solution increases. 003 10.0 points Calculate the temperature at which pure wa- ter would boil at a pressure of 404 torr. The heat of vaporization of water is 40431 J / mol at 100 C. 1. 85.011 2. 89.1842 3. 75.1136 4. 74.1965 5. 82.7572 Version 026 Exam 1 fakhreddine (51615) 2 6. 81.2316 7. 90.9374 8. 76.9366 9. 86.6584 10. 75.9019 Correct answer: 82 . 7572 C. Explanation: P 1 =760 torr P 2 = 404 torr T 1 = 100 C + 273 = 373 K T 2 = ? H = 40431 J / mol ln P 2 P 1 = H R parenleftbigg 1 T 1- 1 T 2 parenrightbigg R H ln P 2 P 1 = 1 T 1- 1 T 2 1 T 2 = 1 T 1- R H ln parenleftbigg P 2 P 1 parenrightbigg = 1 373 K- bracketleftbigg 8 . 314 J / mol K 41000 J / mol ln parenleftbigg 404 torr 760 torr parenrightbiggbracketrightbigg = 0 . 00281091 K 1 T 2 = 355 . 757 K- 273 = 82...
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Exam 1-solutions - Version 026 Exam 1 fakhreddine (51615) 1...

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