EM 17 EXAMINATION February 1, 009 Dr. Kimberly M. Broekemeier NAME: P 1 1 P1 R T T1 ln = - ( - ) l = r l = 8 1/ r l = (4/3 1/ )r onstants: c = 3.00 X 10 8 m/s h = 6.63 X 10-34 J x s R = 0.0806 L x atm/mol x K = 8.314 J/mol x K I A II A III B IV B V B VI B VII B VIII I B II B III A IV A V A VI A VII A inert gase s 1 1.008 3 Li 6.941 11 Na.98 19 K 39.10 37 Rb 85.46 55 s 13.9 87 Fr (3) 4 Be 9.01 1 Mg 4.31 0 a 40.08 38 Sr 87.6 56 Ba 137.3 88 Ra 6.0 1 Sc 44.96 39 Y 88.91 57 * La 138.9 89 * Ac (7) Ti 47.90 40 Zr 91. 7 f 178.4 104 Rf (61) 3 V 50.94 41 Nb 9.91 73 Ta 180.9 105 Db (6) 4 r 5.00 4 Mo 95.94 74 W 183.8 106 Sg (63) 5 Mn 54.94 43 Tc 98.91 75 Re 186. 107 Bh (6) 6 Fe 55.85 44 Ru 101.0 76 Os 190. 108 s (65) 7 o 58.93 45 Rh 10.9 77 Ir 19. 109 Mt (66) 8 Ni 58.71 46 Pd 106.4 78 Pt 195.0 110 (69) 9 u 63.55 47 Ag 107.8 79 Au 196.9 111 (7) 30 Zn 65.37 48 d 11.4 80 g 00.5 11 (77) 5 B 10.81 13 Al 6.98 31 Ga 69.7 49 In 114.8 81 Tl 04.3 113? 6 1.01 14 Si 8.09 3 Ge 7.59 50 Sn 118.6 8 Pb 07. 114 (89) 7 N 14.01 15 P 30.97 33 As 74.9 51 Sb 11.8 83 Bi 08.9 8 O 16.00 16 S 3.06 34 Se 78.96 5 Te 17.6 84 Po (10) 9 F 19.00 17 l 35.45 35 Br 79.90 53 I 16.9 85 At (10) e 4.003 10 Ne 0.17 18 Ar 39.95 36 Kr 83.80 54 Xe 131.3 86 Rn () 58 e 140.1 90 Th 3.0 59 Pr 140.9 91 Pa (31) 60 Nd 144. 9 U 38.0 61 Pm (147) 93 Np (37) 6 Sm 150.4 94 Pu (4) 63 Eu 151.9 95 Am (43) 64 Gd 157.3 96 m (47) 65 Tb 158.9 97 Bk (47) 66 Dy 16.5 98 f (51) 67 o 164.9 99 Es (54) 68 Er 167.3 100 Fm (53) 69 Tm 168.9 101 Md (56) 70 Yb 173.0 10 No (54) 71 Lu 174.9 103 Lw (57)
Part I: Fill-in / Short Answer (49 points total) 1) onsider the following molecule. Lone pairs are not displayed Actual bond angles may differ from those drawn in the figure. All atoms obey the octet rule. 14 O 1 13 N 11 9 10 O 1 3 4 5 6 7 8 a) Identify the hybridization of and N10. sp N10 sp 3 b) Identify the bond angles. -3-13 10 o 6-7-8 180 o c) ow many σ and π bonds are in this molecule? σ 13 π 5 d) ow many unhybridized p orbitals are in this molecule? 10 e) ow many non-bonding pairs of electrons are in this molecule? 5 f) Identify the bond type and orbitals from each atom that participate in the bonds between 5 and O6. σ bond sp of and sp of O orbitals π bond p and p orbitals ) onsider the structure of a molecule that has been determined to have a trigonal bipyramidal electron density arrangement around the central atom. Around the central atom are two non-bonding regions. The rest are bonding regions. a) onsider the structure if one non-bonding pair were placed in an axial position and one non-bonding pair was in an equatorial position Is this the preferred structure with minimum repulsions? b) If the structure in a) is not the preferred structure, what would be the preferred placement of the non-bonding pairs? If it is the preferred structure select one equatorial and one axial ( yes no ) ( both equatorial both axial one equatorial and one axial none of these ) c) What would be the molecular shape of this molecule in its preferred structure? T- shaped 3) Dichloroethene ( l ) can exist in three different isomers (different bonded forms), all of which have the two carbons bonded to each other. Draw the Lewis diagram of each and label them A, B, and. l l Which of the structures are polar? Which two structures can be interconverted by breaking a pi bond? 4) ircle the quantity in each pair that is greater. l A B a) boiling point of F boiling point of l A and b) vapor pressure of 3 3 vapor pressure of 3 3 c) Δ vap of 4 Δ vap of 3 l d) Br bond enthalpy Δ fus Br l l B and a sigma bond? _any two l
5) onsider the O anion to answer the following questions. (sσ), (sσ * ), (pσ), (pπ x )=(pπ y ), (pπ x * )=(pπ y * ), (pσ * ) eleven valence electrons σ* a) In the molecular orbital diagram to the left, place the electrons of the O anion in the appropriate orbitals? π* π * b) Is this species paramagnetic or diamagnetic? paramagnetic π π c) What is the bond order for the O -- anion?.5 σ d) What is the bond order for the O + cation? e) ircle the species with the shortest bond length O -- O O + σ * f) ircle the species with the strongest bond. O -- O O + σ 6) Use the following phase diagram of a hypothetical compound to answer the questions below. a. If the pressure on this compound is increased, its melting point temperature ( increases decreases remains constant ) b. Which point represents a gas to liquid conversion? c. What phase is this compound in at point G? gas d. If the substance is at the conditions of point B and pressure decreased to 0.5 atm, circle the phase transition that occurs: evaporation condensation deposition sublimation freezing melting 7) onsider the orbitals shown below. Place the correct orbital type (chosen from the list) on the blank. a. A. hybrid orbital B. s atomic orbital b. A. p atomic orbital D. d atomic orbital E. σ bonding molecular orbital c. E F. σ* anti-bonding molecular orbital G. π bonding molecular orbital. π* anti-bonding molecular orbital d.
PART II: MULTIPLE OIE (33 POINTS TOTAL) 1. In which one of the following molecules is the central atom not sp 3 hybridized? a. 4 c. l e. SF 4 b. O d. N 3 f. S. When compared to anti-bonding molecular orbitals, the bonding molecular orbitals a. hold more electrons d. are formed from only s orbitals b. have electron density concentrated between nuclei e. are of higher energy c. form only σ molecular orbitals f. none of these 3. The hybrid orbitals formed from mixing one s orbital and three p orbitals point towards the corners of a(n): a. octahedron c. see-saw e. tetrahedron b. equilateral triangle d. triagonal bipyramid f. cube 4. Which one of the following molecules exhibits only London dispersion forces? a. SF 6 c. N 3 e. SF 4 b. O d. PF 3 f. ( 3 ) 3 N 5. Which one of the following cations would exhibit the highest ion-dipole forces of attraction with water? a. Na + c. Rb + e. Mg + b. Sr + d. Al 3+ f. In 3+ 6. Which pair of orbitals, coming together on the x axis, would not form a sigma bond? a. s and sp c. p x and p x e. sp 3 and sp 3 b. p y and p y d. p x and s f. s and dsp 3 7. Which one of the following molecules exhibits the greatest London (dispersion) forces? a. 4 c. F 4 e. Br 4 b. 3 Br d. Br f. Br 3 8. A particular solid substance is soft and melts at a low temperature, to form a liquid which does not conduct electricity. It is a. a metallic solid c. an amorphous solid e. an ionic solid b. a covalent solid d. a molecular solid f. a semiconductor 9. Of the following oxides, which are basic? i. ao ii. ro 3 iii. O iv. P 4 O 10 v. SO a. i. only c. iii. and v. e. none b. i. and ii. d. ii. and iv. f. all
10. ow much heat energy is evolved when 10.0 g of a certain liquid freezes at its melting point? Its molar mass is 78.1 g/mol, its molar enthalpy of fusion is 5.50 kj/mol and its molar enthalpy of vaporization is 0.0 kj/mol. 5.50 kj/mol x 0.1 mol = a..56 kj c. 1.8 kj e. 0.704 kj b. 3.91 kj d. 0.56 kj f. 0.550 kj 11. The graphite (G) structure of carbon is a conductor while the diamond (D) structure is an insulator. Which best explains this property difference in carbon? a. G is sp hybridized, while D is sp 3 hybridized. d. G is a molecular solid while D is a covalent solid. b. G is amorphous, while D is crystalline. e. G is soluble in water and D is not. c. G is soft, so electrons can migrate through it more easily. f. G is ionic, while D is atomic. Part III: Problems (18 points total) Do three of the following four problems. Place an X through the number of the problem you do not want graded. Show your logic and work. Include units on the final answer. 1) Determine the kj of heat energy needed to convert 300 g of liquid methanol, originally at 10.0 o to gas phase methanol at 100.0 o. The following data, heat capacities ( p ) and phase change enthalpies pertain to methanol ( 3 O) at 1 atm pressure. Melting point (T 0 m) = -97.7 o Boiling point (T 0 b) = 64.0 o molar mass = 3.04 g/mol p (s) =.08 J/g x K p (l) = 3.01 J/g x K p (g) = 1.95 J/g x K 0 vap = 35.3 kj/mol 0 fus = 3.16 kj/mol mol 300 g x = 9.36 mol 3.04 g Step 1: warm liquid from 10 o to 64 o 3.01 J x 300 g x 54 K = 48.76 J g x K Step : convert liquid to vapor 35.3 kj 1000 J x 9.36 mol = 330 kj x mol kj = 330,000 J Step 3: warm vapor from 64 o to 100 o 1.95 J x 300 g x 36 K = 1,060 J g x K Δ = 48,76 J + 330,000 J + 1.060 J = 400,03 J ) Using information from problem 1 above, calculate the vapor pressure, in Torr, of methanol at 5.0 0? One set of data is the normal boiling point and associated enthalpy of vaporization P 1 = 760 torr P = X torr Δ vap = 35.3 kj/mol = 35,300 J T 1 = 64 0 + 73 = 337 K T = 98 K P 1 1 P1 R T T1 ln = - ( - ) ln = - (0.00336-0.0097) ln = - J 35,300 P 1 1 ln = - mol ( - ) 760 torr J 98 K 337 K 8.314 mol x K P 446 K 760 torr P 1 446 K x 0.00039 = -1.656 760 torr K P -1.656 P = e and = 0.1909 and P 145 torr 760 torr 760 torr
3) Iridium crystallizes in a face-centered cubic unit cell. The density of iridium is.65 g/cm 3. What is the radius of its atoms? Present the answer in pm. atoms 1 mol g 4 x x 19..65 g 3 = cell 6.03 x 10 mol 3 3 3 cm ( 8) -1.65 g 1.76 x 10 = and r =.489 x 10 3 3 cm.63 r 3-4 - 1-8 10 m 10 pm r = 1.355 x 10 cm x x = 135.5 pm cm r m 4) ommercial hydrofluoric acid, F(aq), is 55.0 % F by mass. Determine the (a) molality, and (b) Molarity The density of this solution is 1.04 g/cm 3 (a) molality mol 55 g F x =.749 mol F 0.008 g kg 46 g O x = 0.046 kg 1000 g.749 mol m = = 61.1 m 0.046 kg (b) molar concentration 45 g O + 55 g F = 100 g total mass 3 cm ml L 1.04 g 3 cm 1000 ml 100 g solution x x = 97.66 ml x = 0.09766 L solution.749 mol F = 8.15 M 0.09766 L solution