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exam 2 - Ansari Usman Exam 2 Due Nov 7 2007 11:00 pm Inst...

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Ansari, Usman – Exam 2 – Due: Nov 7 2007, 11:00 pm – Inst: Brodbelt 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Brodbelt CH301 Exam 2 November 7, 2007 This exam has 31 problems. Programmable calculators and cell phones are prohibited. Bubble in your correct EID and version code! 001 (part 1 of 1) 10 points Assume a molecule AB 4 has ten shared elec- trons in which A has an expanded octet. The central atom is “A” and has no lone pairs of electrons. The atoms surrounding A are represented by B. Pick the true statement. 1. It has two single bonds and two double bonds. 2. It exhibits resonance. correct 3. It has a trigonal bipyramidal electronic geometry. 4. It has a seesaw molecular shape. 5. It must be an anion. 6. It is sp 3 d hybridized. 7. A has five regions of high electron den- sity. Explanation: The structure for AB 3 is A B B B A molecule exhibits resonance if more than one Lewis structure can be drawn. In this case the double bond could be between the central atom and any of the B atoms. 002 (part 1 of 1) 10 points At a temperature of 300 K, all gases (like He, Ar, Kr) have ? average kinetic energies and they have ? . 1. different; different average velocities. 2. different; the same diffusion rates. 3. the same; the same diffusion rates 4. the same; different average velocities cor- rect 5. the same; the same average velocities 6. different; the same average velocities Explanation: T 1 = 100 C + 273 = 373 K T 2 = 300 C + 273 = 573 K r. 003 (part 1 of 1) 10 points At constant temperature, the rate of effusion of H 2 is 1. twice that of helium gas. 2. None of these 3. four times that of oxygen gas. correct 4. one-fourth that of oxygen gas. 5. one-half that of helium gas. Explanation: Rate of effusion of O 2 Rate of effusion of H 2 = p MW H 2 p MW O 2 Eff O 2 Eff H 2 = r 2 32 = 0 . 25 = 1 4 Eff O 2 = 1 4 Eff H 2 004 (part 1 of 1) 10 points If a molecule of AB 2 has 2 lone pairs of elec- trons on A, what would you expect the B-A-B angle to be closest to? A is the central atom
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Ansari, Usman – Exam 2 – Due: Nov 7 2007, 11:00 pm – Inst: Brodbelt 2 and follows the normal octet rule, and B are the bonded atoms. 1. 62.5 degrees 2. 120 degrees 3. 109.5 degrees correct 4. 90 degrees Explanation: This molecule fits the general formula AB 2 U 2 . These structures, which have 4 re- gions of high electron density, have tetra- hedral electronic geometries, and they have bond angles close to 109.5 degrees. 005 (part 1 of 1) 10 points Gas X has a larger value than Gas Y for the van der Waals constant “b”. This indicates that 1. the molecules of X are larger than the molecules of Y. correct 2. the molecules of gas X repel other X molecules. 3. the molecules of X have stronger inter- molecular attractions for each other than the molecules of Y have for each other.
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