322a lab quiz 2 spring 06 blank

322a lab quiz 2 spring 06 blank - CHEMISTRY 3223L W W WSPJ7...

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Unformatted text preview: CHEMISTRY 3223L W W WSPJ7 BY Rage NAME_________________—____ l.(15) 2 . (13) Lab time 3. (12) T.A TOTAL (40) This test comprises this sheet If told to limit the number of words in an answer, DO SO. and three numbered pages. Also, deduction if any part ofananswerisnnnzresmnaile Lethem Tests‘ywizl} be available from your TA at lab and office hours 2 Apr aha—86, and if you initial here ————— > , will be put out in the Study Room by 5 pm. Fri Apr #11? ALL tests, whether in the Study Room or Dr. Ellern's office, will be thrown out on May 2'. Elm mu is Wed, May 1,) 11-1 in SGM 124 (lecture room). - 1 _ 1.(9)(a)(3) Regarding the prep of methylpentenes from 4-methyl-2- 2. pentanol and aq H2804: a higher total yield of methylpentenes. Use of 60% rather than 70% H2804 gives State whether average carbocation lifetime is longer or shorter in 60% acid, then explain the yield results, using <15 words. thing about alkene mixture composition. ZERO if say any (b)(4) Write a minimum path mechanism for the isomerization of 4—methyl—1-pentene, (Cfli3) 2CH{CE{=CH{CE{3. (c)(2) Is Kequil >1 for (b) above Yes No tene mixture --------- > (a)(2) Write HB above the peak associated wit the highest hailing component- (b)(2) Peak area is taken as "Xb-h". For the peak labelled 3, mark its height. (6) Note the gas chromatogram of a methylpen- h (c)(2) Given that an unknown GC peak, X, is known to be due to either cpd A or cpd B. Suppose one adds authentic A to the or nal mixture and then re-runs the GC. is in fact due to A, tell how the GC w change; use <10 words. igi— If X ill (CH3)2CHCH2CH=CH2, to 4-Me-2-pentene, Show each bond-breaking and bond—making step distinctly; regard H3O+ and H20 as the acid and base. ‘—"7 ‘._ _§ , l"'“====l""" Il-l-I-.ll-III a I Ill-ll:===I,: ‘Il-IIIIII== mil-IIII-lr‘ |====II====4 - III-IIIIIII' . III-IIII-Ilv ‘ lI-I-Il-III - II-IIIIIIII - IIIIl-lllI-x- IIIIIIIIIII IIIIIIIII-l‘»\ VII-Ill..- :Jllllll-II . i iiiivv I I I 'E E. II 'I . : II“? TulI-II-I ' ' ll “III-III..- III1 II III-IIIIIIIII II- II “III-III...- _ ll lull-III...- 7:5: 1- I::a:::aga:::::=:: .gi J? “i I II“ ~a E‘ “ii! II!!! E! !-"‘ l: 'S'iilillili "IE 3. (13 points this page) - 2 - (22) (a)(3) In the last experiment, you studied the Br2-catalyzed isomeri- zation of I, cia—X-CH=CH—X (X = COOMe) to the trans isomer, III. The Br-containing radicals II-gauche and II—anti, gener- al structure Br-gH——-$H- , are intermediates. X X Based on the behavior of the two 512 _ggn;aiging Iggggigg mixtures, describe the visual evidence that the main and side reactions both involve Br attack on I; use < 13 words. Answer only THIS question; ZERO for practice test answer. (b)(6) Write only a set of chain propagation reactions for I » III in which the chain carrier is II—gauche. Sum the reactions, then explain briefly how the sum shows that II—gauche is catalytic. (c)(4) 0.80 mmole Br2 (MW = 160) reacts with 2.88 g I (MW = 144). All the Br2 is consumed, while 75% of the I is converted to III; some I is left unreacted. (1) Calculate the mass of III produced, and (2) the initial mole ratio of I to Brz. -3- Ques 3(continued) (d)(3) Use of more Br2 can increase the conversion of I to III. All the Brz reacts to give solid by—product(s). Recalling how one purified III, explain in <20 words why use of more Brz may make getting a good yield of very pure III difficult. (e)(6) Suppose the I 9 III Kequilib in solution, Keq,soln = 1, and that the main driving force for the reaction is the crystalli— zation (xtln) of III. This amounts to viewing the reaction as two steps: I » supercooled liquid III (IIIscl) a IIIcryS' (1) Given that mPIII = 102°(375 K), that the average differ- ence in molar entropy (S) between solid III and scl III = 20 cal/K, and that Gscl ‘ Gsolid = ‘(Sscl ' Ssolid)'AT' calculate ‘5G for crystallization of scl at 22°(295 K). Remember, this process must be spontaneous; Zkatln,22° must be < O. (2)(i) Calculate Kequilibrium based on result of (1), using ln K = —(AG/RT) and taking RT = 590 cal. (ii) Tell in <12 words what this Keq means. (3) Solid A's solubility is 1.0 g A per 10 g §olvent at 20°. A warm solution of A in S comprises 40 g A in 100 g of sggu. Calculate how much A will precipitate on cooling the warm solution to 20°. ...
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