Chemistry 1210, Section 1 Third Hour Exam November 21, 2011 Instructions: Do not begin until 8:30 AM. The exam must be turned in by 9:20 AM. Enjoy your thanksgiving break! This exam should have 25 questions. Each question is worth 4 points for a total of 100 points. A periodic table should be on the next page. Use only a #2 Pencil to mark the best answer on the ScanTron Sheet. You will turn in only the Scantron sheet. You should keep the rest of the exam. Information: h = 6.63 x 10 34 J s c = 3.0 x 10 8 m/s 1 J = 1 kg m 2 /s 2 Av# = 6.02 x 10 23 R = 0.0821 L atm/mol K λυ = c λ = h/mv E = q + w E = hυ M1V1 = M2V2 H = HfinalHinitial H = (n Hproducts) (n Hreactants) q specific heat = Q k 1 Q2 lattice energy = m ΔT d Z eff = Z S H = D (bonds broken) D (bonds formed) Bond D Bond D Bond D H H 436 C H 413 C C 348 C C 614 C C 839 C N 293 C N 615 C N 891 C 358 C 799 C 1072 C S 259 N H 391 N N 163 N N 418 N N 941 N 201 N 607 H 463 146 2 495 S H 339 S S 266
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3 1. Which of the following is the correct electron configuration for the Molybdenum (III) ion, Mo 3+? a. [Kr] 5s 2 4d 1 b. [Kr] 5s 0 4d 3 c. [Kr] 5s 2 4d 9 d. [Kr] 5s 2 4d 7 e. [Kr] 5s 0 4d 5 2. The following electron dot symbol could represent which element(s) in the Periodic Table? a. only C b. any element in row 6 of the periodic table (n = 6) c. any element in group 6A of the periodic table d. any element in group 8A of the periodic table X e. C, Si, or Ge 3. Which of the following is NT isoelectronic with Kr? a. As 3 b. Rb + c. Y 3+ d. I e. all of these are isoelectronic with Kr 4. Which of the following is a correct definition of electronegativity? a. The energy change that occurs when a neutral atom gains an electron b. the ability of an atom in a molecule to attract electrons to itself c. The energy required to remove an electron from the neutral atom d. both (a) and (c) are correct definitions of electronegativity e. all of the above are correct definitions of electronegativity 5. Which of the following cations would have the greatest lattice energy when combined with S 2 in an ionic compound? a. K + b. Ca 2+ c. Rb + d.cs + e. Ba 2+ 6. Referring to the following bonds, which order is correct for decreasing polarity (most polar first)? AsBr GeBr GeCl SeBr a. GeCl ; GeBr ; AsBr ; SeBr b. GeCl ; AsBr ; GeBr ; SeBr c. AsBr ; SeBr ; GeBr ; GeCl d. SeBr ; AsBr ; GeCl ; GeBr e. SeBr ; AsBr ; GeBr ; GeCl
4 7. Multiple bonds, when formed between two defined atoms such as C and N, tend to be (i) and (ii) than single bonds. a. (i) stronger; (ii) longer b. (i) weaker, (ii) longer c. (i) weaker, (ii) shorter d. (i) stronger, (ii) shorter e. it depends on the type of bonds that are present. 8. How many total valence electrons are present in the carbonate ion, C 3 2? a. 28 b. 32 c. 22 d.24 e. 20 9. In order to satisfy the octet rule, which of the following atoms will want to form 3 bonds? a. Li b. B c. Al d. N e. S 10. In drawing Lewis structures for the following species, which one has an atom that does not satisfy the octet rule? a. C b. C 2 c. N d. N 2 e. N 3 11. What are the formal charges on the phosphorus atoms in each of the following possible Lewis structures for the phosphate anion: 3 3 (i) (ii) (iii) P P P 3 (i) (ii) (iii) a. 1 +1 +2 b. 1 0 +1 c. 2 1 0 d. +2 0 2 e. +1 0 1
5 12. What is the oxidation number on the S atom in sulfuric acid, H 2 S 4? a. +6 b. 0 c. +8 d. 4 e. +4 13. How many equivalent resonance structures can be drawn for (i) the nitrate ion (N 3 ) and (ii) the carbonate ion (C 2 3 )? a. (i) 1 (ii) 1 b. (i) 2 (ii) 2 c. (i) 3 (ii) 3 d (i) 2 (ii) 3 e (i) 3 (ii) 2 14. Using the information in the table of average bond energies on Page 1 of this exam, estimate ΔH (in kj/mol reaction) for the combustion of acetylene according to the following balanced chemical equation (be careful to use the right bond energy values and numbers of bonds, and look carefully at the reaction stoichiometry!): 2 HC CH + 5 2 4C 2 + 2H 2 a. +757 kj b. 2439 kj c. +485 kj d. 3265 kj e. 757 kj 15. Valence shell electron pair repulsion (VSEPR) theory is based on the idea(s) that a. atoms in molecules are restricted to 4 bonds, or 8 total electrons around each atom. b. Electron domains arrange themselves in such a fashion as to minimize the interaction between each electron domain c.. double and triple bonds count as a single electron domain for the purpose of predicting electron pair geometry d. both (b) and (c) are correct e. all of the above are correct 16. In the Lewis structure for SF 4, S has (i) lone pairs of electrons and (ii) bonded pairs of electrons. a. 0, 4 b. 1, 4 c. 2, 4 d. 4, 8 e. 4, 1
6 17. What are the electron pair and molecular geometries in XeF 2? Electron pair geometry Molecular geometry (a) linear linear (b) tetrahedral bent (c) trigonal planar bent (d) Trigonal bipyramidal bent (e) Trigonal bipyramidal linear 18. Which of the following molecules does NT have a trigonal planar molecular geometry? a. CH 2, where C is the central atom b.n 3 c. PF 3 d.bcl 3 e. both (a) and (c) 19. Which of the following molecules is/are polar? a. CH 2, where C is the central atom b.n 3 c. PF 3 d.bcl 3 e. both (a) and (c) 20. What hybrid orbital set would be used for the central atom of a molecule that has a trigonal pyramidal molecular geometry? a. sp b. sp 2 c. sp 3 d. sp 3 d e. d. sp 3 d 2 21. Draw a Lewis structure for hydrogen cyanide, HCN. Then answer the following: the bonding in HCN is best described by how many TTAL bonds, and of which types: a. two sigma bonds and two pi bonds b. three sigma bonds and no pi bonds c. three sigma bonds and one pi bond d. three sigma bonds and two pi bonds e. two sigma bonds and three pi bonds 22. The following is the structure of acetic acid (vinegar). According to valence bond theory, what hybridizations would you predict for the indicated atoms?
7 H 3 C C H ii i iii What hybridizations would you predict for the indicated atoms? a. i sp 3 ii sp 3 iii sp 3 b. i sp 3 ii sp 2 iii sp 2 c. i sp 3 ii sp 2 iii no hybridization d. i sp 3 ii sp 2 iii sp 3 e. i sp2 ii sp2 iii no hybridization 23. What are the orbital hybridizations on bromine in the following compounds: (i) Br 3, (ii) BrCl 3? a. (i) sp 2 (ii) sp 2 b. (i) sp 3 (ii) sp 3 c. (i) sp 3 (ii) sp 3 d d. (i) sp 3 d (ii) sp 3 e. (i) sp 3 (ii) sp 2 24. Which ion in the isoelectronic series below has the smallest radius? a. Al 3+ b. Na + c. 2 d. F e. Ne 25. The angles in a perfect tetrahedron are 109.5, and those for a trigonal plane are 120. Based on its Lewis structure, what would you predict for the bond angles in ammonia, NH 3? a. 109.5 b. 107 c. 112 d. 120 e. 124