NAME Chemistry 413 Examination November 3rd 1992. This exam is in two sections (total 100 points). Section 1 should be answered in the blue examination booklet provided. Section 2 is multiple choice and must be answered on these sheets by circling the appropriate answer. WRITE CLEARLY!! IT WILL HELP ME TO UNDERSTAND YOUR ANSWER AND PROBABLY GET YOU MORE POINTS!! Section 1. (1). Use VSEPR Theory to predict the structures of the following molecules and assign a point group symmetry to each. Show all work, including which operations are present for the simpler point groups. (3 points each) (a) XeO 2 (b) NH 3 (c) PF 5 (d) SF 6 (2). Determine the point group symmetry of the following. Show all work, guesses will receive NO CREDIT! (3 points each) (a) Ferrocene (staggered) Fe (b) Fe Li (c) (d) (e) Tetrachloroallene (f) Borazine (planar) H H B H C C C N N B B H N H H 1
(3). The following Xenon compounds are listed in decreasing order of acidity. Suggest a reason for this trend. XeO 2 F 4 > XeO 3 F 2 > XeO 4 > XeOF 4 > XeO 3 (5 points). (4). Suggest Autoionization possibilities for IF 3, IBr, and BrF 5, and probable structures of the ions formed. (6 points). (5). Compare the relative acidities of the group 13 and group 14 halides within each group. If there are any unusual trends, explain them. (10 points) (6). SF 4 and SF 6 are known. OF 2 is known but OF 4 and OF 6 are not known. Suggest a reason for this. (3 points) (7). Suggest a synthesis for polymers containing the following atoms in the backbone. (a) P and N (4 points) (b) Si and O (4 points) (c) S and N (2 points) (8). What is meant by the terms "Hard" and "Soft" when they refer to Lewis acids and bases? (4 points) (9) Explain what is meant by CLOSO, NIDO and ARACHNO in polyhedral boranes. Suggest a molecule (B x H y ) for each of these structure types. (6 points) SECTION 2. MULTIPLE CHOICE (CIRCLE ONE ANSWER ONLY) (1 point each) 1. Nearly all of the Group 1 metal compounds are ionic with very limited covalent character. However, one Group 1 metal ion promotes more covalent character than the other metal ions in that Group. Identify that ion. a) Li + b) Na + c) K + d) Rb + 2. Since the Group 1 metals are readily they are strong agents. a) oxidized; oxidizing b) oxidized; reducing c) reduced; reducing d) reduced; oxidizing 2
3. In the presence of excess oxygen potassium, rubidium and cesium form a) normal oxides b) peroxides c) superoxides d) hyperoxides 4. Chemically, a sapphire is a) KAl(SO 4 ) 2 12H 2 O. b) aluminum chloride that contains trace amounts of Be 2. c) aluminum oxide that contains some transition metal ions. d) NaAl(OH) 4. 5. Which halide ion is most readily polarized? a) F - b) I - c) - d) Br - 6. Except for fluorine, the halogens show four positive oxidation numbers. What are those oxidation numbers? a) +1, +3, +4, +6 b) +1, +3, +5, +6 c) +3, +4, +5, +6 d) +1, +3, +5, +7 7. When the equation is balanced for the preparation of antimony pentafluoride from fluorine and the metal, what is the sum of the coefficients in the balanced equation? a) 10 b) 8 c) 7 d) 9 8. When forming interhalogen compounds, what determines which halogen will be the central atom? a) The smaller of the two halogens is the central atom. b) The halogen with the higher first ionization energy is the central atom. c) The less electronegative of the two halogens is the central atom. d) The halogen with the higher standard reduction potential is the central atom. 3
9. Select the strongest oxyacid. a) HBrO 3 b) HBrO 4 c) HBrO 2 d) HBrO 10. How many sulfur atoms are there in the solid sulfur molecule? a) 1 b) 2 c) 6 d) 8 11. The `rotten egg' smell is due to a) H 2 S b) HCN c) H 2 SO 4 d) SO 2 12. Arrange the Group 16 hydrides in terms of decreasing acid strength. a) H 2 Se > H 2 S > H 2 Te b) H 2 S > H 2 Te > H 2 Se c) H 2 Te > H 2 Se > H 2 S d) H 2 S > 2 Se > H 2 Te 13. The gas SO 2 is the anhydride of which acid? a) H 2 SO 4 b) H 2 SO 3 c) H 2 SO 2 d) HSO 14. What is the formula of selenous acid? a) H 2 SeO 4 b) H 2 SeO 2 c) H 2 SeO 3 d) HSeO 4
15. When ammonia undergoes autoionization, what is the formula of the Bronsted-Lowry base that forms? a) NH 2 OH b) NH 2 - c) NH 4 + d) N 2 H 4 16. The bond angles in hydrazine, N 2 H 4, should be about a) 120. b) 90. c) 109. d) 180. 17. Fresh nitric acid is colorless whereas the aged acid has a yellow or brownish color. What compound is responsible for this color? a) NO b) N 2 O c) NO 2 d) O 3 18. How many phosphorus atoms are present in the white phosphorus molecule? a) 6 b) 4 c) 2 d) 8 19. Phosphine, PH 3, is the phosphorus analog of ammonia, but it is a much weaker base. The K b of PH 3 is about 10-26 while the K b of NH 3 is 10-5. What does this suggest about the occurrence of phosphonium (PH 4 + ) salts? a) The weak base means that PH + 4 ions are quite common and therefore many salts are known. b) The occurrence of PH + 4 ions is not related to the base constant K b. c) Such salts should be rare since there is little tendency for phosphine to form PH + 4 ions. d) Phosphonium salts are very stable. 5
20. How many acidic hydrogens does phosphorous acid, H 3 PO 3 have? a) 1 b) 2 c) 3 21. What are the products of the "water gas" reaction? a) CO 2 and H 2 O b) CO 2 and H 2 c) C and H 2 d) CO and H 2 22. Although silicon dioxide has the empirical formula SiO 2, it is a network solid that is based on interconnecting a) cubes. b) hexagons. c) tetrahedra. d) octahedra. 23. The very high melting point of SiO 2 (quartz melts around 1600 C) suggests that a) the intermolecular bonding in SiO 2 in not like the bonding between CO 2 molecules. b) the Si-O bond is very strong. c) SiO 2 is very stable. d) all of the above 24. Silicone polymers, since they contain Si-O bonds, should be a) resistant to heat and attack by chemical agents. b) rigid and resistant to deformation. c) solids. d) readily vaporized. 25. What is the hybridization on B in boric acid, H 3 BO 3? a) sp b) sp 3 c) sp 2 d) dsp 3 26. If diborane (B 2 H 6 ) had a `normal' structure - borons bonded to each other and three hydrogens bonded to each boron - how many electrons would be required? How many electrons are actually available for bonding? a) 14 electrons; 12 electrons b) 14 electrons; 16 electrons c) 12 electrons; 14 electrons d) 16 electrons; 14 electrons 6