Chemistry HW 9 - Kim Eugene Homework 9 Due Nov 6 2007...

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Kim, Eugene – Homework 9 – Due: Nov 6 2007, midnight – Inst: McCord 1 This print-out should have 23 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Room Assignments for EXAM 2 A-Ma WEL 3.502 Mc-Z WEL 2.246 001 (part 1 of 1) 10 points Identify the kinds of intermolecular forces that might arise between molecules of Br 2 . 1. None of these 2. London forces, dipole-dipole, hydrogen bonding 3. London forces correct 4. dipole-dipole 5. hydrogen bonding 6. London forces, dipole-dipole Explanation: Br Br is non-polar. 002 (part 1 of 2) 10 points 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. 0.76 2. 0.24 3. 0.63 4. None of these 5. 0 . 39 correct 6. 0.52 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 003 (part 2 of 2) 10 points Which ion will attract a water molecule more strongly? 1. Equal attraction 2. Al 3+ 3. Be 2+ correct Explanation: The attraction of the Be 2+ ion will be greater than that of the Al 3+ ion. Even though the Be 2+ ion has a lower charge, its radius is much smaller than that of Al 3+ , making the attraction greater. 004 (part 1 of 1) 10 points Which of the following cations is likely to be hydrated in compounds? 1. NH + 4 2. Rb + 3. Li + correct 4. Cs + 5. K + Explanation: Li + is the smallest. 005 (part 1 of 1) 10 points Which of the following compounds is UN- LIKELY to be commonly available and thus not found in the laboratory? 1. BaCl 2 · 2H 2 O
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Kim, Eugene – Homework 9 – Due: Nov 6 2007, midnight – Inst: McCord 2 2. La(NO 3 ) 3 · 6HO 3. Na 2 CO 3 · 10H 2 O 4. KCN · 2H 2 O correct 5. CuSO 4 · 5H 2 O Explanation: K + is only a +1 cation AND it is too large to substantially attract waters of hydration. +2 and +3 cations will generally form hydrates. Na + will also attract water due to its smaller size. 006 (part 1 of 1) 10 points What would be the most significant type of intermolecular forces in a liquid sample of fluoroform (CHF 3 )? 1. hydrogen bonding 2. dispersion 3. covalent 4. ionic 5. dipole-dipole correct 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-
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