Exam 01 - ycs73 EXAM1 Fakhreddine(53605 This print-out...

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ycs73 – EXAM1 – Fakhreddine – (53605) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. 001 12.0 points How many grams o± water at 80.0 C must be added to 10.0 grams o± ice at - 20 C to result in ONLY liquid water at 0 C? 1. 12.5 g 2. 22.4 g 3. 68.8 g 4. 74.0 g 5. 21.2 g 6. 1.25 g 7. 11.2 g correct 8. 25.0 g 9. 56.6 g 10. 109.2 g Explanation: 002 10.0 points We observe the ±reezing points o± ±our di²erent aqueous solutions as ±ollows: Solution A ±reezes at - 0 . 10 C; Solution B ±reezes at - 4 . 00 C; Solution C ±reezes at - 10 . 00 C; and Solution D ±reezes at - 13 . 00 C. In each solution, the solute is a non-volatile non-electrolyte. Which solution should be expected to have the highest boiling point? THINK!! No calculation should be necessary! 1. Solution B 2. Solution D correct 3. Solution A 4. Solution C Explanation: Δ T f = K f m m = Δ T f K f Δ T b = K b m m = Δ T b K b K f The ±reezing point lowering is inversely pro- portional to the boiling point elevation, which means that the solution which ±roze at the lowest temperature will boil at the highest temperature. 003 12.0 points Methanol (CH 3 OH) and ethanol (C 2 H 5 OH) are common organic solvents. The vapor pressures o± pure methanol and pure ethanol at 25 C are 122 . 7 torr and 58 . 9 torr, respec- tively. I± the mole ±raction o± CH 3 OH in the mixture o± the two solvents at 25 C is 0 . 35, what is the mole ±raction o± C 2 H 5 OH in the vapor phase that is in equilibrium with the liquid mixture? 1. 0 . 241 2. 0 . 471 correct 3. 0 . 321 4. 0 . 556 5. 0 . 641 6. 0 . 161 7. 0 . 404 Explanation: P methanol = 122 . 7 torr χ methanol = 0 . 35 P ethanol = 58 . 9 torr χ ethanol = 1 - χ methanol = 1 - 0 . 35 = 0 . 65 .
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ycs73 – EXAM1 – Fakhreddine – (53605) 2 P methanol = χ methanol P methanol = (0 . 35)(122 . 7 torr) = 42 . 945 torr . P ethanol = χ ethanol P ethanol = (0 . 65)(58 . 9 torr) = 38 . 285 torr . From the ideal gas law n P , so χ methanol = n methanol n methanol + n ethanol = P methanol P methanol + P ethanol = 42 . 945 torr 42 . 945 torr + 38 . 285 torr = 0 . 471 . 004 8.0 points Colloids 1. do not exhibit random molecular mo- tion. 2. do not exhibit the Tyndall efect.
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Exam 01 - ycs73 EXAM1 Fakhreddine(53605 This print-out...

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