C2510_Exam_Key_Fall_2008 - Name: TA: First Lab Day (Circleo...

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Unformatted text preview: Name: TA: First Lab Day (Circleo e): M T W Th F LabTime (Circle one): AM PM Cornell University Chemistry 25 10 Examination November 18, 2008 Instructions: Read all questions completely before answering. You may find it helpful to first read through the entire exam and then answer those questions that you find easier and later return to those you find more difficult. Please follow the directions for each _ question as answers that are not written where or how it is specified in the question will lose all credit. Good Luck! !! Signature: Page 1 of15 1) (15) a) An aqueous solution containing 5.0 g of solute in 100 mL is extracted with three 25-mL portions of diethyl ether, where the distribution coefficient (K) (aka the partition coefficient) is7 (K=7). What is the total amount ofsolute that will be at; 4 p extracted after the three extractions? You mustfizlly Show work to get any credit. K4‘ 3%; ,s 1L L waif/3’3 isr / loo“ - A6. w i HEM?) 5.x " "5?; ‘- 7 ‘ ‘ ' 'WL w=n~W "x: X7— .2ng “" mat; F: ? '5 {Egg}: __ [75X l/X: [28"?X _L-§,3_i‘.. ‘ hie—x H'x : (M? K: We loomL 3C4 g Lg;«{.(lg:0.éb€r 41x: a59~2x L K/ = r :0? 1&7: affix 1. 0% m; 4‘64 X 27 b) The original aqueous solution In (a) £336? is instead extracted one time with a 100- mL portion of diethyl ether. What is the total amount of solute that will be extracted in this single extraction? You mustfulbz Show work to get any credit. Kr? .“Z' 50:”). X XI?Y%< 51X [ WWL Page 2 of 15 2) (15) You have a 1.0 g sample of Benzoic Acid that is contaminated with 0.23 g of Salicylic Acid. Use the following water solubility data below to answer the questions for this problem. Compound Solubility (0°C) g1; Solubiligfi g 100°C! gJL Benzoic Acid 1.7 68 Salicylic Acid 2.17 66.6 a) What volume of boiling water is needed to completely dissolve the 1.0 g of benzoic acid? You must fully Show work to get any credit. 58% x; .ZZ b) How much benzoic acid will remain in solution at 0°C when the fully dissolved benzoic acid solution from (a), above, is cooled? You must fully Show work to get any credit. IRE amia: aaw i, * er c) Will all of the salicylic acid remain in solution at 0°C? You must fully show work to get any credit. e@0% 8,233. x 0:061. :2 0:033? fifdbéalpg M vim“ a d) Will the benzoic acid be pure at the end of this recrystallization (yes or no)? 9% . Page 3 of 15 3) (13) True or False? Write “T” on the line before each statement for true and “F” for false. E A Broken glass should be left in the waste hood. _/ k B When trying to warm a solid in a solution in order to dissolve it, you want to make sure the flask is tightly sealed so that no liquid evaporates. C Sandals are allowed in the lab when the weather is warm. " D Safety goggles are to be worn on the forehead. E The safety shower is to be used immediately when you are on fire. WWNW F The best thing to do in a chemical fire is to immediately pour water on it to extinguish the flames. / r G When a flask is on fire on your hotplate, the first thing you should do is turn the hotplate off to reduce the energy going to the fire. l fl Your Cornell organic lab has at least two means of exit. I It is best to dry solids on the bottom shelf of the oven so it is closer to the heating element. NW J A compound with a warning of “lachrymator” means it causes reproductive problems in women. / i, K If your clothing catches fire in the lab, you should immediately go to the fire blanket and use it to extinguish the flames. L The red emergency phone outside your labs automatically dials the Cornell police when the receiver is picked up. F M Dirty glassware should be washed with acetone in the sink. . Page 4 of 15 4) (12) Briefly describe six things wrong in the following attempt at a reflux set-up. <— Waler In —> Water Oul Lab Bench Top 1. 100 dump on Q?) mask 2. SGUch. VIO+ €(Eua‘gbb 0g; 3. Wadi! #0 COWOQQVLSE/ WW9 £94957sz 4. ample/[gar {/las S‘éJf’FE/ M Ff. 5. No 88‘)” bay/507F013; OLUYS F/mI/IIZ. 6. IQQHUKEHLWV) fob—0J6 be pfowe: M lnooofl. - WW‘HQ L2: ’99 I CSP‘ o (“7(6 7? W5? a6 gas/30w us M51424!) /47L(0 Page 5 of 15 5) (5) Circle the shape elow that best represents a monoclinic crystal. 7) (15) Propose a reasonable mechanism to account for the formation of the following observed minor reaction product(s). —-* H 0%? Page 6 of 15 8) (I2) Refer to the following phase diagrams for miscible two component mixtures when answering the questions below. Phase Diagram Y Phase Diagram X 100 150 E e “ 2 '5 a E e 2. Ear- E 80— l.) 0 I- E— l | WA 0.5A LOB 1-0A 05A 1.013 0.5 B 0.5 B Composition mole fraction Composition. mole fraction Phase Diagram Z 175 E 3 E 8. E 95 H | 10A 0.5A LOB 7 2:780‘ I 0.513 Composition. mole fraction 3) Which mixture (X, Y, or Z) is the best candidate for a simple distillation? V b) Which mixture (X, Y, or Z) is the best candidate for a fi‘actional distillation? X c) Which mixture (X, Y, or Z) cannot easily be purified by distillation? 2 (1) Draw a vapor temperature (y-axis) vs. drops (Jr-axis) graph of what you would see for a distillation of mixture Z that was 75% component A and 25% component B. Label temperatures on your graph. Page 7 of 15 9) (12) Refer to the following silica gel TLC plate taken of a reaction’s progress at time = 0, 20, 50, 80, and 100 minutes when answering the questions below. The solvent used is 10% ethyl acetate in hexane. Solvent Front 0 20 5080 100 Time of Reaction ( minutues) a) At what time (earliest time, in minutes) does it appear clearly that the reaction is finished? 80 b) How many reactants can you say with surety are used in the reaction? (Circle the one best choice below) A) One C) Three D) Four E) One or Two F) One, Two, orThree C) One, Two, Three, or Four H) Three or Four I) Two or Three 0) How many products can you say with surety are generated in the reaction? (Circle the one best choice below) A) One B) Two C) Three D) Four E) One or No )One, Two, or Three G) One, Two, Three, or Four H) Three or Four I) Two or Three Page 8 of 15 10) (20) Sally A. Mide has really goofed up. She is the lab technician for the organic labs at Kornell University. She had four standards ready for a TLC lab for the students. She filled four reagent bottles with one each of the four compounds and then she lost track of which was which! Unfortunately, it was the last of the compounds as well. Her boss, Dr. Evil, has promised to fire her if she makes any more mistakes. DeSperate to figure out which was which, she obtains an IR spectrum of each. Those Spectra, labeled A, B, C, and D are shown on the following 2 pages (pages 9 and 10). Sally has asked for your help. Find the spectrum that is most consistent with each compound shown below. Write your answer (A, B, C, or D) on the line below each structure. Page 9 of 15 S ectrum A "mmlil Page 10 of 15 S ectrum C MNMEIII I" “9‘ #l S ectrum D [W ruin-1mm 3 "Ga M m "n 100‘ m mm« 50 ‘5 N 6‘ K 04 SO Page 11 of15 11) (I5) Propose a reasonable mechanism to account for the formation of the following observed reaction product(s). <4__ ffifig‘éfr-f /( C4,; . I Page 12 of 15 12) (10) A chermst w1shes to carry out a gravity silica gel column chromatographic separation using diethyl ether (CH3CH200H20H3) and ethanol (CH3CH20H). a) With which solvent should the chemist begin the elution? A74 do‘hw chrmfifiivq’rayfi? r5 abwaayg UJ mtg [535' Sb/umj— "" All b) What would happen if the chemist started with the other solvent? ( (436 We mm, ,ana/ 30A:er WU COW/7 M (W firm/5A )2; Cd/me od/ ([fiew/Mo SWMm- 13) (20) Stew A. Flask has a huge problem He had done the chalcone lab and has four compounds in separate flasks on his desk. Two are starting materials and two are possible products of his reaction. The possible structures of the four compounds are shown below. Please match them to the spectrum, on the following pages (labelled A, B, C, and D), most consistent with each structure. Write the letter (A, B, C, or D) on the line below each structure. 5 C Page 13 0f15 Hutu-(11:: mIl-fl Page 14 of15 Spectrum C HID ninth-(am 8 my; _ {M IIWIU'IIEIID 11' E 52 u H IO 56 Page 15 of 15 14) (5) Circle the picture below which best indicates the refractometer is properly adjusted for reading the refractive index: B) D) A) Illuulunllllllllllll Immumrmmm "llllfillllllluu5;}; mnm'iillll [nu \ llllll‘ll'l‘Ill‘I'I' llllllllll {uninhith II',"'%3'_{\:\I\‘.‘.\- » H 15) (8) Why must a solid drying agent be removed from a solution before the solution is distilled? m Fe I‘WJ&J alt37l77(a‘l1¥»\ m‘f/ CM‘SB m hymn) owe/ml; l2: old/weal; W0) [ECU/{\lLat/mhafe we ArSé‘flemmFé («01% Wag/fl 16) (10) In an extraction, name two ways of determining which layer is the top layer in the separatory funnel. Methodl: 9r 2' 5 9.914% / 6/ u x' f “’7’ El. ofer Mg fife; £2347 MethodZ: 056 erM5/;%, 0.5 at garage/Wen Mammal 1% al?: 12% We slaw/r a; 1569' /a ,«m‘o J (Db Cyfiate/ M9 OESEWE. 5.25:4 (S 17) (8) When a compound is contaminated with a small amount of an impurity, it shows a depressed and broadened melting point range. Why? We MMQWS heme”, fir; +000 m up, 5/ gut) 5/9014” q /a4/7é/ WOW-’39 W 771056 0x. We STD/“J / fad/74": ‘14 bmoJémAA—a 7=y€%/€gfgjf ...
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C2510_Exam_Key_Fall_2008 - Name: TA: First Lab Day (Circleo...

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