Chem%20161-2009%20final%20exam%20%2B%20answers

Chem%20161-2009%20final%20exam%20%2B%20answers - Chemistry...

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1 Chemistry 161 Final Exam December 17, 2009 + Answers Chem 161-2009 Final exam Hill, Petrucci et al. Chapter 11 – States of Matter and Intermolecular Forces Structures and types of solids (e.g., crystal structures) 1. A unit cell of TiO 2 contains one Ti 4+ ion in the center of each face. What is the total number of ions contained in that cell? A. 3 B. 6 C. 8 D . 9 E. 10 Since there are six faces, and one-half of the atom in each face belongs to the unit cell, then there are 3 face-centered Ti 4+ ions in the unit cell. Since the ratio of Ti 4+ to O 2- is 1:2 in TiO 2 , then there must be 6 O 2- ions in the unit cell (perhaps one atom from the corners, three from the edges, and two in tetrahedral holes). The total ions in that cell is therefore 9. The question doesn’t rule out the possibility of there being more than 3 Ti 4+ ions. However, if there were more than 3, e.g., 4, then there would be at least 8 O 2- ions, with a total number of ions of at least 12, which is not an answer option. Chem 161-2009 Final exam Hill, Petrucci et al. Chapter 3B - Stoichiometry Reaction stoichiometry 2. Consider the following series of unbalanced reactions: FeO(s) + O 2 (g) Fe 2 O 3 (s) Fe 2 O 3 (s) + KCN(aq) K 3 Fe(CN) 6 (aq) K 3 Fe(CN) 6 (aq) + K 2 S(aq) Fe 3 S 4 (s) + KCN(aq) Assuming 100% yield, how many moles of Fe 3 S 4 can be produced from six moles of FeO? Also, assume O 2 , KCN, and K 2 S are all present in excess. A . 2 B. 3 C. 4 D. 5 E. 6 2FeO(s) + O 2 (g) Fe 2 O 3 (s) Fe 2 O 3 (s) + KCN(aq) 2K 3 Fe(CN) 6 (aq) 2K 3 Fe(CN) 6 (aq) + K 2 S(aq) (2/3)Fe 3 S 4 (s) + KCN(aq) Note that in the above equations, it is only necessary to balance the linking components: 2FeO Fe 2 O 3 2K 3 Fe(CN) 6 (2/3)Fe 3 S 4 6 m o l ? m o l 6molFeO x ((2/3)molFe 3 S 4 /2molFeO) = 2.0 mol Fe 3 S 4
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2 Chem 161-2009 Final exam Hill, Petrucci et al. Chapter 11 – States of Matter and Intermolecular Forces Intermolecular forces (e.g., H-bonding) 3. Which of the following species is expected to have the lowest vapor pressure? A. CH 4 B. CH 2 Cl 2 C. NH 3 D. CH 3 OCH 3 E . CH 3 OH The molecule with the lowest vapor pressure would be the one with the strongest intermolecular force. A. CH 4 is London forces (weak). B. CH 2 Cl 2 is a dipole-dipole force (moderate). C. NH 3 is hydrogen bonding (moderately strong). D. CH 3 OCH 3 is dipole-dipole interaction (moderate) E. CH 3 OH is hydrogen bonding (moderately strong) Both C and E are hydrogen bonding. An O-H hydrogen bond should be stronger than an N-H hydrogen bond, because O is more electronegative than N. In addition, the fact that CH 3 OH is a liquid, while NH 3 is a gas, further demonstrates that CH 3 OH has the stronger intermolecular force. Chem 161-2009 Final exam
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This note was uploaded on 03/08/2011 for the course CHEM 161 taught by Professor Vacillian during the Fall '08 term at Rutgers.

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Chem%20161-2009%20final%20exam%20%2B%20answers - Chemistry...

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