Chem 625 Midterm Exam Answer Key

Chem 625 Midterm Exam Answer Key - Mswefil KEN Chem 625...

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Unformatted text preview: Mswefil KEN Chem 625 Midterm Exan‘t‘t‘i‘ March 13, 2008 8:00-10:00 pm Room 1001 Malott 60 points (20 questions - 3 points each) Please be sure to fill in your Name, Student ID Number and Laboratory Section Number on .your scantron. Tuesday AM - Susanthi 84234 Tuesday AM - Steven Tuesday PM - Tony Acid HCI Rcom Hzco, PhOH RfiWH tho cu‘ 54213 54217 pKa 6.5 10 1.0 I 5.7 Wednesday PM - Tony 54219 Thursday PM - Briana 54221 Saturday AM - Susanthi 54215 Base acoz- ' nco; “10' 11,1» - 'OH n30 _ Use the following reaction information to answer questions 1-3. M Br + NaCEN ———> MCEN + NaBr Acetone 1-bromobutane Sodium Cyanide Butyl cyanide Used 300 mg Used 101 mg Isolated 162 mg MW = 137.02 glmol MW = 49.01 glmol . MW = 83.13 glmol d = 1.28 gImL mp = 563 °C d = 0.795 g/mL bp =100°C bp=139°C 1. When setting up reactions, liquids are easily dispensed using micropipets. Calculate the volume of 1—bromobutane necessary to perform this reaction. A) 0.11 mL B) 0.38 mL C? 0.59 m: . m 2. Calculate the theoretical yieldvof the reaction. l.,— meo bwtawv : 29 g; E3 300 m ‘ MO \ : ‘w1\a1 MD\ E) 247 "1% tooom'] “51.013 " Mam“ mm“ kg 5 mb\ {DOUMaj “FLOW? oOO'LDUMoquCN \wmtwq. ' i l 0 ' _ r 3. if the reaction does not consume all of the 1-bromobutane. an appropriate technique to separate the butyl cyanide from 1-bromobutane? A) water/ether extraction E Ye 0+ { a \ B) acid/base extraction 0} m Mp MMDU M3 is C) suction filtration DE simEle gistillgifian n ‘ \ess AMA/n 4. After running his reaction, Max takes a melting point of his previously unknown compound and observes a melting point range of 123-125 °C. Can he assume that his compound is pure based on this melting point? A) Yes. the sharp melting point range indictates the compound is pure B 7 ‘ m- — -- -- edthemeltin Lo [9 0 he could haveaml ure - I o, i eme - - 1 00 95 A —s c 5.5!“.- “small-II I-ImW-II-II ,5 V I... ‘ ,0 III-ll-ll-I- -- - Temperature (°C) I-Iflll-I I-II-III- 65 l 60 “In-I- 0% Benzoic‘ Acid ' 05%", x 100% Benzoic Acid 100% Triphenylmethane 39$Wm 0% Triphenylmethane Composition 5. After an extraction of benzoic acid and triphenylmethane, the two white solids get mixed up on the benchtop. Vlflsely, you decide take a melting point of one of the samples to clear up the confusion. The melting point range of the sample is 70-95 °C. What is the composition of the sample? A) 20% triphenylmethane : 80% benzoic acid = i° u’l Ilt3'lzl— ' 0% benzoicacid C 35% triphenylmethane: - o nzorcacl I A o o“ - ' me ne: '- nzorcacl E) 100% triphenylmethane : 0% benzoic acid 6. If a sample at the eutectic composition is heated to 75 °C. what is the nature of the sample? A) vapors of benzoic acid and triphenylmethane B) pure liquid benzoic acid and a solid mixture C) pure liquid triphenylmethane and a solid mixture lid 4 r o: oic acid and trihen Imethane Iqw mixture of benzorc am an I eny me ane 7. Predict the order of elution of the following compounds using a reverse phase C18 stationary phase on a chromatographic column. 0 OH O ' ,H / CI + _ \OM ii“ M (CH3CH2)4NBT 1 2 3 4 5 «K [45- ?!)‘kV meg-POM Y‘ s. A 3. 4, 2,5and C) 2,1,4, an g) §.§.1.gangi Reverse, phase - vwn polar 5%.?W ‘ ) , ,5, an 8. Not so average Joe Was running a column on Al203 to separate his desired compound from an impurity. He spotted his fractions on a SiOz TLC plate. developed it in a chamber and realized something was not right. Mat is wrong with his TLC plate? D) The wrong mobile phase was used to develop the TLC plate E) The Rf values are are not far enough apart to separate on a column. 9. Limonene, an organic component of spearmint oil has a normal boiling point of 178 °C. If the system pressure is is changed to 50 mmHg, what is the expected result? A) the vapor pressure of Iimonene will be lower B) the boiling point of Iimonene will be higher C) the my ‘ . . . nene will remain at 178 °C “\W ’ LI) e ilin 'ntoflimon ' -: ower bm\\‘\‘\ more In orma on IS necessary to determine the result “4 M51" 0 “M ' N0 «W; . * a: W“ ~R emce1£ oweSSm-c o? .‘a reflux lou'mml ‘Pm‘n-i- of: 0(5vavava 10. In the lab, (+)-tartaric acid was added to racemic methylbenzyl amine to form diastereomeric salts. Changes in which of the following physical properties allowed for the separation of these diastereomers? A meltin m- ' . Wham“, Wm ., ' :3 bgon factgrcm Sic2 7)"? M a Y t N 0‘ Sbwwe/ D) boiling point tonne w W Wow r “mama E) optical rotation 11. Two extractions are performed on a reaction that affords 4.0 g of benzylamine as the product. Assuming that 3.4 g of the benzylamine is partioned into the organic layer after two extractions. calculate the volume of methylene chloride (CHZCIZ) that was used for each extraction. (Hint both extractions will use the same volume) = I Y\ sglurfigHzO: 135 mL Wit-LP ; Wu H b \l «- A) 88 mL 1' “19 W) B) 4 mL . . 3,443 Home m 2m}. W mL so OM a) "(‘{Whlé N'\ WW3 \Q/VCV 1.. o u ff...— 4‘05 Q’s-k 1. o |§ L \‘5? X ' f' \3S*’(‘ZT\ ‘/~ __ 295’ 5‘2. ‘1' "a?" "$5— .. l i a I as, | .fdny ‘ mg” ; 313 12. Choose the appropriate name for the glasswar Etured below. X : 1Q - ‘ I" e "i as C) filtration flask D) West condenser E) round bottom flask For questions 13 and 14, use the following information Racemic thalidomide was a drug prescribed in the late 1950's to help control morning sickness. Sadly. it was found that the (S)-enantiomer resulted in severe birth defects in infants. 0 o , | N o | N--- 0 NH NH 0 o o o (S)-thalidomide (R)-thalidomide [a] = + 58.2 ° [0.] = - 58.2 ° 13. Mich of the following techniques could be used tq separate the enantiomers of thalidomide? A) add HCI B Si lumn chromatora lemmmmu D)pe orm ractIOna'l - " ' E) polarimetry hy 14. The sample of thalidomide after the separation rotates plane polarized light 27 ° counterclockwise. Mat is the optical purity of your sample and which enantiomer is in excess? A) the sample is racemic B)54%ee; (S) Cave: e) 0%: “2'10 rm ;, Au you; Likfloea with (at . as we ‘ «$5 . emei‘ommot (Madmen is (.5 M LR) trim—timer \s Me;qu Use the following phase diagram to answer questions 15—17. Temperature (°C) Illllnmll IIIIIIMII “II-“III 60 45% twaw 10W 2 ta I 0% 2-pentanone 55% Will 0° 'Pen "one 0 A: ethyl acetate 100% ethyl acetate Composition , 15. Wnat type of mixture does the above diagram represent? A = 9 C) liquid mixture with low boiling azeotrope D) non ideal liquid mixture‘that follows Henry's Law E) mixed solid solution 16. A Sample composed of 80% ethyl acetate and 20% pentanone (X) is heated to 82 °C, what is the composition of the liquid phase? A 55% on - one: 45% eth lacetate ‘ o pentanone: "e y acetate % ntanone: 50 eth lacetate o pen «I‘ . y — E) 22% pentanone: 78% ethyl acetate 17. How many steps of a fractional distillation would be necessary to obtain pure ethyl acetate if the composition of the intial sample is 84% pentanone and 18% ethyl acetate (Y)? ‘ “"" A) 1 taxi) C) 9 D)11 E)15 The following separation scheme was carried out. To answer questions 18-20, first work through the separation t/Aqueous layer is neutralized with excess NaOH. then separated by suction filtration , "\7 Wash with saturated NaHCOssoln evaporate ether and run standard SiOz column Aqueous Phase #19 Aqueous Phase Solid that‘is filtered off #18 Compound which elutes first from column #20 18. A) 5 B) 1 C) 2and4 E) 1and2 19. A) empty B) 2and3 C) 1and2 D) 3 E)5 20. B) 2 C) 3 D) 4' E)5 ...
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Chem 625 Midterm Exam Answer Key - Mswefil KEN Chem 625...

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