207.Prelim1.2007 - K 21 (Last) (First) Cornell Student ID...

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Unformatted text preview: K 21 (Last) (First) Cornell Student ID Number Lab Instructor’s Name Lab Section (Day and Time) Chemistry 207 Preliminary Examination 1 October 4, 2007 Time: 7:30 PM — 9:00 PM Please do not open the exam until told to do so. You have 1.5 hours to complete the exam. This exam has 10 pages, none of them blank. Page 10 shows a periodic table and various constants and equations. Before beginning work, make sure your exam is complete. Write directly on these pages. Show all of your work and indicate units where necessary. You may turn in the exam at the front of the room when finished. 1. (30) __ 2. (30) _ 3. (25) _ 4. (30) __ 5. (30) _____ 6. (30) TOTAL (175) r-x 1. [7pm] (a) Light shines onto a metal surface, and the speeds of any ejected electrons are measured. Sketch a plot of electron speed versus increasing wavelength of light. Your sketch should illustrate what this measurement teaches us about the physical world. For > >>° I m. C,“ We (gee-tel - I. FOP )<>o ‘LJ Vg’l‘. elcclnm / J 5(9ch,’\"._ 0 )0 >5 49 >. 2 (/1, J flrcfiulal wwcluyl’l- [7pm] (b) A chunk of iron is maintained at a temperature of 500 0F, and the brightness of emitted electromagnetic radiation at various frequencies is measured. The experiment is repeated at 1000 0F. Sketch one graph of brightness versus increasing frequency showing the results of these two experiments, labeling each plot with the temperature. Efiokl'fit 35 O l" ‘OQQQF Nd“: has 4am? T J Vch-c )l‘ q-«X TAMSH-j T [8pts] (c) This plot of an atomic orbital shows curves of constant probability. The probability of finding the electron in the shaded region is 40%. Name this orbital, and sketch a plot of its radial probability distribution. 1 Y‘ath mule fink 1’ afl-DW “’ “Al-t! 1Qfljq\grn.g\e .._..:9 Q:1 -=7 ‘7 orLth Z “bit; '—‘9 “3-3 , 3P orLAxLI [8pts] (d) Draw two-dimensional cross-sections of a surface enclosing 95% of the electron probability for a Is orbital for Ar, C, and Na atoms. Your labeled sketches should indicate any differences among the surfaces for these three atoms. Far 15 crL'|‘l"D-,CflJ—l“fi} DNMUVH futréxcec are srhru) 5o K~ScccHM5 «rm Cur-ulu‘. Rs .24" e- 4m; Ltu dqu n MGM.“ sa F<vhwj l, u a 1‘. O 0 N47 i‘l\ Hr] ..—- 2. [15pm] (a) Copper (Cu) atoms occur in nature with two different masses. The more common type has mass 62.9296 u and natural abundance 69.17%. How many protons and how many neutrons are contained in the nucleus of the less common type of Cu atom? \Sbhfc-qvcrsugl wuss FV‘d'V“ PMahg Ah.le 64- Cq: C3.S"l(u arm. 2 0.£‘lfl((91.‘\u0 +0- mam HM M, ii «an ‘Sah‘Y-e 63-5“: = 93.51.23 + 0.30% M a; -_~ rm) #qrom :- 2 1‘ ’ #hcfimg: Q9. ‘51 : iEC.) [15pts] (b) Give electron configurations for the following species. Use notation that abbreviates the noble gas configuration, and shows electron spin. In your configurations, n should increase from left to right. Ge(Z=32) Cary uuuuu 3.2 1. _‘L._ '54 9:5 “(r Hg (2:80) C. l (Xe) it’flzlb’lL/lblkfilr lfliki “l 3. The electron in a Li2+ ion is described by a rip" orbital, for parts (a) and (b) of this question. [ I Opts] (a) What is the shortest wavelength of light that could be emitted by this ion. Slofik” “fide‘uh , limb.“- Uxtroy h:‘-l OE 5' "2le _l___ _ l :- q if R H (Lin... (16) H “2} -13 = Latixm 3‘ Ofrlfll= lai- >.:: L-C- :l.O3XIO‘8W\l 9: DE [I5pts] (b) Li ht is absorbed by the ion, causing an electron to fly off with speed 1.60 X106 m s' . What is the frequency of this light? l'wv Z: Tbn\l—¢¥\M {mar-J? + C.“ lc'vxgl-tc {may n = U: ) I : 21m. _., fl. :2“ :ll.13xlo“w$ qt lc #——-—————— kuagkg E = giM‘Vt-‘L :. %(1||\x16«217(|‘g0xi°c)u j ‘: llJ'l-xlo‘ls‘rl Lv '1: 2."‘IDX’°-‘9T iv 2 3,:2x10"He r—x [30pts] 4. Caffeine contains by mass 49.48% carbon, 5.15% hydrogen, 28.87% nitrogen, and 16.49% oxygen. A 12.00 fluid ounce can of a popular cola contains 55.00 mg of caffeine, equivalent to a caffeine concentration of 0.0007981 M. What is the molecular formula of caffeine? F} "J’r {Mc‘nfiCc‘ Hrn‘K)‘ . Txke, ‘07) 3 C£%M. _.—.—.—..-__.‘_ “HG—Ha L 2 {Luz M“ C] SWIS‘DH ___\5‘.|1M.\ H I lidbn Dmd“ l,0¢g appl'd M” :iZ.OGM.\'N [ ‘L-“fia‘” :- '““°°1 a*~““‘ ' Irmwamk‘ ‘l..l.<33 ("I‘ll Hy-h H‘LDC ©L01 (HUM: HHJLL N1.” 0‘ 4 EH! HYNLO fww mu a two mm +Zl|~1\ Mr. 2* \‘H and“ 3 fiTo 131} MQ\Q (VJ Mr L‘fh‘alfi) nch MQ\QCKL‘I Mic 5 JJ M Q . ————._ Melts c('%<_-IM in. CCK'W 2 5—5355 h.‘ lcquL Va‘wm cl Cam -: Itch «i-I. up. ‘ L \ ___ 0.35'LialL 33.31% {—l. we. (Lomafim m : r3161: an L“ (leaa]Mc[o,3$“11\ ML 2 75“” ‘3- \\4L\ C) “A” l a. 1 (o‘ooo1‘18’n (km? ( 35‘“ N 4”?“ QMPZrKJ QIu-vwl‘ MUSJ Mb\(£‘\“/‘ thm\% 2-. H16 Mg CL A H f" 5. (a) [8pm] Carbon forms single covalent bonds with each of the elements N, S, 0, Cl. Rank the bond lengths of C-N, C-0, C-8, and C—Cl . < C~S C‘O C‘“ < C‘Cl — < — shortest bond longest bond [8pm] (b) Rank these atoms according to first ionization energy: Ne, K, He, Cl . \< < c \ < Na < H { lowest II highest I1 [7pts] (c) An exception to the general rule for predicting relative atomic sizes is the case of Cd (2:48) and In (Z249). Which atom is larger, and Why does the mle failin this case? ’— \ H Mold-J Rum Shim M rt «1 m» . _L,{r m1 kaQ-I A“ r1“ 5 I Ta = Crow” 33‘- S‘FV mm c m 5‘? f" ‘- h I. CA: (try-H” 53 d Mk, c M 5-3 5117:“ ML; 31 LL qu'i’lun Qf‘w “Kath-s “Ha-m $5, 'HM. C‘l’kc} *1 lacreghd 11H. (TM Cl.) T4. Cuuflkl’ALR-fla [7pm] (d) The first ionization energies of P and S are nearly identical, contrary to the usual trend. Why does the rule for variation of ionization energy fail in this case? quq {7:11.741 Mud I‘ 1‘ or, 23:; I 5,, j:\(5\ 51-“qu 'u [gag A» 1‘ m . 93 CM] 35"- 3¢3 a, out) 351 _'LL I. 3? 5‘. LNG) 354‘ij or (rod 131. 4:1 l 3? P has {Rh-«n- ghkl,‘ \/.L_£Llla.\ 3, [LLLJL‘{\\ I “‘qu wall Aux AIL-nan all m immakm. IMBHAJ S (real—2.5 “‘6 Wamfskm . {Ll-IQ |‘«c.r{c\<_ 3:“ $“)\ Kean...» I‘D} J ConKkuU‘a-«J 7% china}- «4’ 2m [53) 2:55. 6- (a) [20 PIS] In an indUStl‘ial Process, NH3 , 02, and CH4 react to produce HCN and water. 10.0 kg of each reactant are mixed in a reactor, and the reaction proceeds to completion. What mass of NH3 remains in the reactor? WH3 Jr £101 + CH“ Ab ch +3HLO w :' iSBA‘ MU “H3! “HWU 01- : “£03 3 wu‘“ 31.61 and" 5-5-1 CH ‘0; '3 ‘4 r M‘\ C’Hb‘ ‘6. o q 0 M‘ ‘fl‘ U“ “\«A . 313 Ma 0L revue; (%}(3,3] M.\ an)“ .I- J *1 Akin] 2 Zofl ho‘. 3 )i‘ O I ‘ih'Hfl . gnu ’WLSQ “\MHHh “1 @ftSEM ., L J - 3 mum-«\— NHJ \t-H twin 2 534 Md ~1o‘H‘J Ciw‘w 6. (b) [IOpts] An element X forms oxides with molecular formulas X0 and X20. A 2.00 g sample of X0 is completely converted in a chemical reaction to 1.47 g of X20. None of the other reactants or products in the process contain X. What is X? X0 4r MM“ ——-; “XLO + more JJMJH- 2.503 2 Z_(\.”|3~5 \ ...
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This note was uploaded on 03/31/2008 for the course CHEM 2070 taught by Professor Chirik,p during the Fall '05 term at Cornell University (Engineering School).

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207.Prelim1.2007 - K 21 (Last) (First) Cornell Student ID...

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