EXAM INSTRUCTIONS/SUGGESTIONS. READ THIS CAREFULLY!

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1 1 EXAM INSTRUCTINS/SUGGESTINS. READ THIS CAREFULLY! YU MAY MIT ANY THREE (3) F THE FIFTEEN 6 PINT QUESTINS N THIS EXAM. IF YU D MRE THAN TWELVE F THEM, NLY THE FIRST TWELVE WILL BE GRADED. ALL THER QUESTINS MUST BE ANSWERED. INDICATE N THE NEXT PAGE WHICH THREE QUESTINS ARE NT T BE GRADED BY WRITING DNG (D NT GRADE) NEXT T PRBLEM NUMBER. N PARTIAL CREDIT on any question except where indicated by the statement SHW WRK. When work is requested, set up equations (with numbers substituted in appropriate units) in space provided, but do the calculations on scrap sheet. IF THE QUESTIN STATES "SHW WRK" AND YU GUESS CRRECTLY WITHUT SHWING WRK - YU GET 1/2 CREDIT. CHECK FRNT BLACKBARD FR CRRECTINS/CHANGES. D THE SIMPLER QUESTINS FIRST. IF ANY QUESTIN IS NT CLEAR - ASK TANUJA R ME ABUT IT! CNSTANTS AND CNVERSIN FACTRS ARE N THE PAGE AT THE END F THE EXAM. PLEASE LK THERE! LAST THREE PAGES ARE FR SCRAP WRK. FEEL FREE T TEAR THESE PAGES FF. FIRST REMINDER: FINAL EXAM N WEDNESDAY, AUGUST 11 th FRM 9 AM T 12 NN. PLEASE REMVE THIS SHEET PRIR T STARTING EXAM.

2 2 CHEMISTRY S144 SECND EXAM 7/29/99 PRFESSR J. MRRW PRINT NAME, LAST: FIRST: I.D.# : MAXIMUM PINT VALUE IS IN PARENTHESIS 1. (6) 9. (10) 17. (6) 2. (9) 10. (20) 18. (6) 3. (10) 11. (6) 19. (6) 4. (20) 12. (6) 20. (6) 5. (6) 13. (6) 21. (6) 6. (15) 14. (10) 22. (6) 7. (12) 15. (6) 23. (6) 8. (8) 16. (6) 24. (6) CLUMN TTALS: (MAXIMUM) (86) (70) (48) EXAM TTAL (186 pts) UT F 1

3 3 1) Ionization Energies (kj/mol) Fe First 759 Second 1561 Third 2957 Fourth 4175 A compound, ilmenite, (FeTi 3 ) is composed of either Fe 2+ and Ti 4+ ions R Fe 3+ and Ti 3+ ions. Which combination, (Fe 2+ and Ti 4+ ) or (Fe 3+ and Ti 3+ ) is more reasonable. (6 pts) SHW WRK 2) Give the electronic configuration (1s 2 etc) and the number of unpaired electrons (UE) in each of the following gaseous atoms/ions. (9 pts - 3 pts each: 2 pts/1 pt) ANSWER IS: Cu UE = Cu + UE = Cu 2+ UE = 3) An ionic crystalline solid, MX 3, has a cubic unit cell. Which of the following arrangements of the ions is consistent with the stoichiometry of the compound? (10 pts) i) M 3+ ions at the corners, X - ions at the face centers. ii) M 3+ ions at the corners, X - ions at the body center. iii) X - ions at the corners, M 3+ ions at the face centers. iv) X - ions at the corners, M 3+ ions at the body center. v) M 3+ ions at the corners and the body center, X - ions at the face centers. ANSWER IS:

4 4 g 4) Magnetite, Fe 3 4 ( mol ), has a density of g 3. It is an cm orthorhombic crystal with a = b = Å and c = Å. How many formula weight units of Fe 3 4 are there per unit cell? How many Fe 2+ ions and how many Fe 3+ ions are there per unit cell? (20 pts) SHW WRK The number of formula weight units is: i) 12 ii) 15 iii) 24 iv) 30 v) 36 5) Pervoskite is a material containing calcium, titanium, and oxygen. The cubic unit cell is shown below. # of Formula weights: # of Fe 2+ ions: # of Fe 3+ ions: X X = Ti 4+ = 2- = Ca 2+ Ionic radii: 4+ Ti = Å; 2- = 1.45 Å density = g/cm 3 Molar mass = g/ m Calculate the unit cell edge length in Å. (6 pts) ANSWER IS: 6) smium is one of the worlds most expensive elements. The abundance of osmium is 2x10-4 ppm (parts per million) and it has a melting point of

5 o C. Last year one kilogram of this element sold for 78 million dollars. Aside from all of this fascinating information, osmium crystallizes in a face centered cubic lattice. The atomic radius of osmium is Å, g and its molar mass is mol. a) Calculate the density of osmium. (10 pts) SHW WRK ANSWER IS: b) Calculate its molar volume ( cm3 mol ). (5 pts) 7) Give the hybridization for each underlined atom in the following ions. Also give the actual spatial appearance of the ion. If the ion cannot exist, write CNE, in space provided. (ie. sp 2 / trigonal) Group numbers: N (5), Cl (7), S (6), F (7) (12 pts - 3 pts each) ANSWER IS: i) IF 4 + / ii) SF 5 + / iii) NF 4 - / iv) BF 4 + /

6 6 8) State how many of each of the following types of elements of symmetry exist in chlorofluoromethane. (8 pts) F NUMBER PRESENT Cl center of symmetry H chlorofluoromethane SP 3 hybridized H two fold axis of rotation, C 2 three fold axis of rotation, C 3 planes of symmetry 9) State how many of each of the following types of elements of symmetry exist in square based pyramid below. (10 pts) center of symmetr c a a = b = c b two fold axis of rotation, 2 C three fold axis of rotation, 3 C four fold axis of rotation, 4 C planes of symmetry

7 7 Use the M correlation diagram below (where needed) to answer questions 10, 11, and 12. σ * 2px π * 2py, π * 2pz σ2px π2py, π2pz σ * 2s σ2s σ * 1s σ1s 10) Predict the apparent bond order, relative bond length, and number of unpaired electrons in the following species; C, BN, and BeC. Where relative values are compared, use < or > otherwise use the calculated numerical values. (20 pts) C BN BeC Bond order Bond Length Bond enthalpy Number of unpaired electrons 11) If light of the proper wavelength is used an electron in the π2py molecular orbital is excited to the π * 2p y. What is the bond order after this transition in BeC? (6 pts) bond order = 12) List the following in order of increasing bond length: Li 2, Ne + 2, and F 2. (6pts) < < 13) The bond order of each of the following, C-H, -H, and F-H, is 1. List them in order of decreasing bond enthalpy. (6 pts)

8 8 > > 14) The molecule BNH 2 Cl 2 exists in two forms, a cis form and a trans form. GIVEN: Bond enthalpies (kj/mol): B=N (511); N-N (163); B-N (212); N-H (388); N-Cl (381); B-H (551); Cl-Cl (243); B-Cl (349) Cl H B = N trans H Cl Cl H B = N cis Cl H J Calculate the energy per molecule, ( molecule ), required to convert the trans form to the cis form. (10 pts) i) 8.48x10-19 ii) 4.97x10-19 iii) 3.52x10-19 iv) 2.67x10-19 ANSWER IS: THE FLLWING PERIDIC TABLE MAY BE F USE IN ANSWERING THE REMAINING PRBLEMS. Group Number Period 3 2 I A II A III A IV A V A VIA VII A Li 1. Na.97 4K.9 Be 1.5 Mg Ca B 5 Rb Sr In C N Al Si P S Se 2.4 F Cl Ga Ge As Br 2.8 Sn Sb Te I Inert gas Beneath most symbols are electronegativity values. Pl use them where necessary in answering this question. 15) List the following atoms in order of decreasing 2 nd ionization energy:, S, and K. (6 pts) > > 16) List the following in order of decreasing radius. Na +, Mg +, and K +. (6 pts) > >

9 9 17) List the ions S 2-, P 3-, and N 3-, in order of increasing ionic radius, that is, the largest is last. (6 pts) < < 18) List the following ions in order of decreasing ionic radius. Li +, Be 3+, and B + (6 pts) > > 19) List the following gases in order of decreasing molecular bond enthalpy P 2, S 2, and Cl 2. Lowest goes last. (6 pts) > > 2) List the following atoms in order of decreasing 3 rd ionization energy. Li, Na, and Al (6 pts) > > 21) Which of these molecules is/are non-polar ; IF 3, BF 3, NF 3, SF 4, XeF 4? (6 pts) ANSWER: 22) Circle the stronger acid in each of the following pairs. i) H 2 S 2 3 or H 2 S 4 6 (3 pts) ii) HI 3 or HCl 3 (3 pts) 23) Match up the following bond enthalpies (in kj/mol), 163, 36, 412, and 436,, with the indicated molecules; (6 pts) H-H C-H C- N-N 24) In a multi-electron atom, how many electrons can have the following sets of quantum numbers? (6 pts - 2 pts each) i) n = 3, m λ = 0, m s = ii) n = 4, m λ = -2, m s = iii) n = 4, m λ = +2

10 10 CNVERSIN FACTRS and PTENTIALLY (BUT NT NECESSARILY) USEFUL EQUATINS C = 3. x 1 8 m/sec = 3. x 1 1 cm/sec h = x J. sec = x 1-27 erg. sec m e = 9.18 x 1-28 g = 9.18 x 1-31 kg ε = hν N A = 6.22 x 1 23 R =.821 L. atm mol. degk = 82.1 cm 3. atm mol. degk λν = c 1 Å =.1 nm = 1-8 cm = 1-1 m λ = h p (debroglie equation) where p = mv Heisenberg Uncertainty principle: P X = h 4π where p = mv kinetic energy: ε = 1 2 mv2 = p2 2m where p = mv q = e =1.622 x 1-19 coulombs = 4.86 x 1-1 esu 1 ev = x 1-19 J ε n = x 1-18 n 2 J ε = qv = hν - Φ UNIT RELATINSHIPS 1 amp = 1 coulomb sec 1 volt. coulomb = 1 Joule 1 esu 2 = 1 erg. cm 1 Watt = 1 joule sec 1 Joule = 1x1 7 erg 1 Joule = 1 kg. m 2 sec 2 1 erg =1 g. cm 2 sec 2

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