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HW08-solutions-QUY - arriaga(yga77 HW08 quy(50970 This...

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arriaga (yga77) – HW08 – quy – (50970) 1 This print-out should have 31 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points What would be the most significant type of intermolecular forces in a liquid sample of fluoroform (CHF 3 )? 1. dipole-dipole correct 2. hydrogen bonding 3. dispersion 4. covalent 5. ionic Explanation: London forces, dispersion forces, van der Waals or induced dipoles all describe the same intermolecular force. London forces are in- duced, short-lived, and very weak. Molecules and atoms can experience London forces be- cause they have electron clouds. London forces result from the distortion of the elec- tron cloud of an atom or molecule by the presence of nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London forces and occur be- tween polar covalent molecules due to charge separation. H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electroneg- ative atoms – F, O or N only. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding. CHF 3 is a polar molecule that does not con- tain H bonds; therefore, dipole-dipole forces will be the most significant type of intermolec- ular forces present. 002 10.0points Forces between particles (atoms, molecules, or ions) of a substance are called 1. intramolecular forces. 2. armed forces. 3. intermolecular forces. correct 4. None of these Explanation: Bonds within molecules or formula units are called intramolecular forces. Bonds between particles are called intermolecular forces. 003 10.0points Which of the following structures represents a possible hydrogen bond? 1. Br H · · · Br 2. Cl H · · · Cl 3. C H · · · O 4. F H · · · F correct Explanation: H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electroneg- ative atoms – F, O or N only. 004 10.0points Identify the kinds of intermolecular forces that might arise between molecules of Br 2 . 1. hydrogen bonding 2. None of these 3. London forces correct 4. London forces, dipole-dipole, hydrogen bonding 5. London forces, dipole-dipole 6. dipole-dipole Explanation:
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arriaga (yga77) – HW08 – quy – (50970) 2 Br Br is non-polar. 005(part1of2)10.0points Calculate the ratio of the potential energies for the interaction of a water molecule with an Al 3+ ion (of radius 53 pm) and with a Be 2+ ion (of radius 27 pm). 1. 0.52 2. 0.24 3. 0.63 4. 0 . 39 correct 5. 0.76 6. None of these Explanation: r Al = 53 pm r Be = 27 pm The energy E p -| z | μ r 2 , so the ratio is E Al E Be = | z Al | r 2 Be | z Be | r 2 Al = | 3 | (27 pm) 2 | 2 | (53 pm) 2 = 0 . 389284 006(part2of2)10.0points Which ion will attract a water molecule more strongly?
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