exam 3 answers - Iype Shelby Exam 3 Due Nov 8 2007 11:00 pm...

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Iype, Shelby – Exam 3 – Due: Nov 8 2007, 11:00 pm – Inst: Vandenbout 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Vanden Bout 2 PM ONLY ! ! ! ! 001 (part 1 of 1) 10 points Two gases are contained in gas bulbs con- nected by a valve. Gas A is present in a 18 L bulb at a pressure of 473 torr. Gas B exerts a pressure of 651 torr in a 73 L bulb. What is the partial pressure of gas B after they equili- brate once the valve has been opened? Correct answer: 522 torr. Explanation: V A = 18 L P A = 473 torr V B = 73 L P B = 651 torr V total = V A + V B = 91 L P B V B = P t V t P t = P B V B V t = (651 torr) (73 L) 91 L = 522 torr 002 (part 1 of 1) 10 points Which of the following is NOT a characteristic of a hydrogen bond? 1. It is responsible for the unusual physical properties of water. 2. It can occur when hydrogen is covalently bound to very electronegative elements liks F, Cl, Br and I. correct 3. It is stronger than other dipole-dipole interactions. 4. It is weaker than a covalent bond. Explanation: Hydrogen bonding only ocurs when hydro- gen is covalently bonded to very electronega- tive elements like O, N or F. 003 (part 1 of 1) 10 points The following experiment was carried out us- ing a newly synthesized chlorofluorocarbon. Exactly 50 mL of the gas effused through a porous barrier in 157 s. The same volume of argon effused in 76 s under the same condi- tions. Which compound is the chlorofluoro- carbon? 1. C 2 Cl 5 F 2. C 2 Cl 2 F 4 correct 3. C 2 ClF 5 4. C 2 Cl 3 F 3 5. C 2 Cl 4 F 2 Explanation: 004 (part 1 of 1) 10 points Consider four molecules I) CHCl 3 II) CH 4 III) CH 3 Cl IV) CCl 4 Which of these exhibit permanent dipole- dipole interactions? 1. I only 2. I and III only correct 3. None of these 4. III only 5. I, III, and IV only Explanation: Dipole-dipole interactions occur in polar molecules. CHCl 3 and CH 3 Cl are polar be- cause their dipole moments do not cancel. CH 4 and CCl 4 are symmetric; their dipole moments cancel and the overall molecule is non-polar. 005 (part 1 of 1) 10 points
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Iype, Shelby – Exam 3 – Due: Nov 8 2007, 11:00 pm – Inst: Vandenbout 2 Which best describes the hydrogen bonding between two water molecules? hydrogen oxygen 1. 2. correct 3. 4. Explanation: Note the water molecules line up as the δ - on the O of one molecule is aligned with a δ + on a H of another molecule. 006 (part 1 of 1) 10 points Under what conditions is a gas most likely to deviate from ideal behavior? 1. low density 2. high pressure correct 3. when considering noble gases 4. high temperatures Explanation: Under high pressure, there are many more collisions between molecules. This increases the likelihood that a non-ideal interaction will occur. 007 (part 1 of 1) 10 points At room temperature which of the following gases will have the fastest average velocity?
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