Exam 2-solutions

Exam 2-solutions - Version 038 Exam 2 McCord(53130 This...

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Version 038 – Exam 2 – McCord – (53130) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. McCord CH301tt This exam is only For McCord’s Tues/Thur CH301 class. IF Quest works properly, you should be able to see your score For this exam by 11:30 PM tonight. Do realize however that Quest has been taking up to 8 hours to get through the grading, so your score might appear bit by bit. I will post an announcement on our web page and/or Quest when I Feel like all bubblesheets have been graded. PLEASE carefully bubble in your UTEID and Version Number! We av- erage about 20-30 students per exam that misbubble this inFormation. Get it right! 001 10.0 points Choose the species that is incorrectly matched with electronic geometry about the central atom. 1. 4 : tetrahedral 2. BeBr 2 : linear 3. H 2 O : tetrahedral 4. 3 : pyramidal correct 5. NH 3 : tetrahedral Explanation: 002 10.0 points IdentiFy the hybrid orbitals used by the underlined atom in acetone (CH 3 C OCH 3 ). 1. sp 2 correct 2. sp 3. sp 3 4. Pure p z orbitals are used in bonding. 5. sp 3 d Explanation: The structure is C H 3 C CH 3 O b b b 003 10.0 points Which oF the molecules I) O H H II) B Cl b b Cl Cl III) Cl Cl b b contains polar covalent bonds but is NOT itselF a polar molecule? 1. III only 2. II and III only 3. I and II only 4. All ft the criteria. 5. None ft the criteria. 6. II only correct 7. I and III only 8. I only Explanation: I) Water has polar covalent bonds and is itselF polar. II) Boron trichloride contains polar covalent bonds but is not polar overall due to symmetry.
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Version 038 – Exam 2 – McCord – (53130) 2 III) Chlorine gas has nonpolar bonds only. 004 10.0 points Which of the following is the correct Lewis formula for thioformaldehyde (CH 2 S)? 1. b b b b b b b b b b b b b b b b b b H C S H 2. b b b b b b b b b b b b b b b b b b b b H C S H 3. b b b b b b b b H C S H 4. S C H H b b b b b b b b b b 5. H b b b b b b C S b b b b H b b b b b b 6. b b b b b b H C S H 7. H C S b b b b H correct 8. H C S H 9. b b b b b b b b b b b b b b H C S H 10. b b b b b b b b b b b b H C S H Explanation: The Lewis formula for thioformaldehyde (CH 2 S) is H C S b b b b H 005 10.0 points The molecule AX 3 is polar and obeys the octet rule; therefore, the central atom A 1. has no lone pairs of electrons. 2. has two lone pairs of electrons. 3. has one lone pair of electrons. correct 4. has four lone pairs of electrons. 5. has three lone pairs of electrons. Explanation: The molecule AX 3 could obey the octet rule in one of two ways. The molecule could contain two A - X single bonds and one A - X double bond, yielding the structure A X X X This molecule would have a trigonal planar geometry. It is symmetrical and therefore non-polar, so this is not the correct structure for our molecule. The second possible dot structure for AX
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This note was uploaded on 10/28/2009 for the course CH 53130 taught by Professor Mccord during the Fall '09 term at University of Texas.

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Exam 2-solutions - Version 038 Exam 2 McCord(53130 This...

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