MidtermFall1999Key

MidtermFall1999Key - Print your name ANSWER KEY 1 Print...

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Unformatted text preview: Print your name ANSWER KEY 1 Print your TA's name ‘ CHEM 2364 Organic Laboratory Midterm Examination October 4, 1999 Dr. Tamara Nauman Dirmfiiqmgz DC) N©T @PEN Y©Ulfii TEST UNTHL EVERVEDNE HAS A C©PYE Prim ymuf mamca and ycamr [email protected]@hin Aggigfiamvg mama; @zm @vcary pacao Print your name ANSWER KEY 2 Print your TA's name Safety 1. (15 pts.) Describe the proper disposal method for each of the following: w a. a glove used during the caffeine experiment Place it in the ordinary trash. b. aspirin dissolved in ethanol ' Flush it down the sink drain with water. c. a test tube used for the Lucas test Rinse the test tube and then dispose of it in the broken glass box. d. a 20 mL solution of 3 M H2804 Flush it down the sink drain with water. e. a broken thermometer Collect the broken glass and give it to Benn in the stockroom. Dust any spilled mercury with sulfur. Sweep up the mercury / sulfur mixture and place it in the mercury disposal jar and return the jar to Benn. 2. (5 pts.) Give two reasons why dichloromethane (DCM) is a good solvent choice for use in the organic lab. 422mm 1. DCM has low toxicity. 2. DCM has no flammability. Print your name ANSWER KEY 3 Print your TA's name Acetylsaligylic Acid and Caffeine A/- solubility B C / Temperature 3. (15 pts.) In regards to recrystallization, for the above solubility vs. temperature graph, explain the solubility of the solute in each solvent A, B, and C. s a v te 'o Solvent A: The solute is soluble in the solvent at all temperatures thus only a small crystal crop would result. Solvent B: The solute is insoluble when the solvent is cold and soluble when the solvent is hot. The insoluble impurities can thus be removed from the solute when the solvent is hot by using filtration. All the solute recrystallizes when the solvent is cold. Solvent C: The solute is insoluble in the solvent at all temperatures thus it is impossible to separate the solute from insoluble impurities. 4. (5 pts.) Using the above graph which solvent A, B or C will be the ideal recrystallization solvent (fill in the box). Solvent Print your name ANSWER KEY 4 Print your TA's name 5. (25 pts.) Describe using a flow diagram how you would separate a mixture of the following two compounds into the pure compounds. acidic compound neutral compound CH3—-(CHZ)3iOH and CH3---(CZ}12)3/IOLNH2 Add DCM and dilute NaOH (or 5 pts. aqueous N 2101-1) and then separate. Aqueous Layer Orgm.____'_c__L_a1__er H20 and DCM and CHg—(Cthj‘o-Nl CHs-(CHzlaj‘ NH2 5 pts. Add dilute HCl (or 5 pts. 1) Dry over anh. MgSO4 aqueous HCl) and 5 pts. 2) Evaporate OR distill DCM and then separate off DCM CH3—(CH2) i 3 NHz Aqueous Layer l Organic Layer Discard DCM and H 1) Dry over anh. MgSO4 5 pts. 2) Evaporate OR distill off DCM CH3—(CH2)3iO H Print your name ANSWER KEY 5 Print your TA's name Thin Layer Chromatography 6. (5 pts.) Which of the following solvents is the most polar? (Circle your answer) 0 CH3 1 b o i a) CH3/LCH3 ) CH3CH20H C) G 6) CH3 OH 9) C1 c1 C1 7. (10 pts.) A graduate student was using TLC to follow a reaction. If the Rf value of the starting material was 0.25 and the Rf value of the product was 0.75, then determine the order of preparation for the resulting plates: (Label in the blanks with the first prepared plate as 1 and the plate prepared at the end of the reaction as 4.) _2______1_____4_.__3_______. 8. (10 pts.) Explain what went wrong in the following TLC experiments (assume the same type of plate was used as in the TLC experiment you performed). TLC plate 1 TLC plate 2 g . E 1 l . TLC plate 1: The solvent used for the mobile phase was not polar enough. TLC plate 2: The initial spot made was too concentrated or too large so trailing resulted. Print your name ANSWER KEY 6 Print your TA's name t—Butyl Chloride 9. (30 pts. total) Aspirin (acetylsalicylic acid), C9H804, is prepared by heating salicylic acid, C7H603, with acetic anhydride, C4H6O3. The by-product is acetic acid, C2H402. C7H6O3 ‘ + C4H603 —""> C9H804 + (321—1402 MW: 13806 g/ mol 102.06 g/ mol 180.08 g/ mol grams: 6.00 g 5.00 g 6.10 g # of moles: 0.0435 mole 0.0490 mole (A) (15 pts.) What is the theoretical yield (in grams) of aspirin when 6.00 g of salicylic acid and 5.00 g of acetic anhydride are used. (B) (10 pts.) What is the limiting reagent? (C) (5 pts.) If the actual yield of aspirin is 6.10 g, then what is the percent yield? (USE: C = 12.00 g / mole, H = 1.01 g / mole and O = 16.00 g/ mole. LABEL and SHOW ALL WORK!!!) 15 points (A) Theoretical Yield: 111016 C7H603 X 1 H1016 = mole C9H804 1 mole C7H603 0.0435 mole C9H804 X g C9H804 = g C9H804 1 mole C9H804 Ageing (B) Limiting Reagent: C7H6O3 (salicylic acid) ipeigt (C) Percent Yield: percent yield = actual yield x 100 theoretical yield 6.10g x 100 = 77.9% 7.83 g Print your name ANSWER KEY 7 Print your TA's name 10. (15 pts.) Number the following carbocations in order of stability (#5 is the least stable and #1 is most stable). + + + + + H2C==I§I--CH2 Qc—CH3 H2C==CH H3c——-c1~12 H3C—Cl—CH3 CH3 CH3 3 1 5 4 2 11. (10 pts.) In the work up of the t—butyl chloride experiment you neutralized the excess acid with sodium bicarbonate solution. Why not use sodium hydroxide solution instead? Explain. (fig EH3 H3C——- ————C1 + OH —-—————> H3C— -————0H CH3 CH3 Sodium hydroxide will react with the t-butyl chloride by an 8N1 mechanism to give back the t—butyl alcohol from which it was made. 12. (10 pts.) Explain why the following reaction does not occur. CH3CH20H + HCl ‘96» CH3CH2C1 In order to transform an alcohol into an alkyl halide using hydrochloric acid, an 5N1 reaction mechanism takes place. The formation of a stable carbocation intermediate is necessary in this mechanism for the reaction to occur. Ethanol would form a very unstable primary carbocation thus the reaction does not occur. Print your name ANSWER KEY 8 Print your TA's name gflalitative Analysis 13. (30 pts.) What qualitative analytical test(s) would give positive results with the following (if no test available for the functional group present then write NONE) {HINT: there should be 10 tests total with some repeated}. - H3 H2c1 Br CH3 CH3 Brz NONE AgNO3 NaI/acetone H 2'4'DNP 2 4 DNP Tollens I — Jones / H £1335 BIZ 14. (20 pts.) Three unknowns, A, B and C, give the following results when tested with the listed qualitative analysis tests of functional groups (where P = positive and N = negative). Determine which structures are A, B and C. Circle the three structures and label with either A, B or C. Positive for ,4—DNP, Jones, FeCl; 9‘13 ch—c—CHZCHZOH CH3 gm mo)K 60” Negative for all l? S? CH3CCH2CH2CH Positive for Mal / acptnne Print your name ANSWER KEY Print your TA's name Luminol 15. (10 pts.) Fill in the boxes with the missing compounds: 2 gogg gggg box N02 N02 COOH NH 0 + I 2 If H N H2 methylene NH COOH glycol 3? aqua C . C—OH —-——-‘> C--OH C(7- ’ CH3NH2 @\H CH3E\I.H2 .0. e h .0. .Rar‘.‘ H .W 1 HO C—OH CHI‘LH ' 2 \" 3632 *—> \§m3 CH3N H }II Print your name ANSWER KEY 10 Print your TA's name Cyclohexene 17. (5 pts.) If water boils at 100°C and cyclohexene boils at 83°C, why during the initial fractional distillation performed during the cyclohexene experiment does material boil over at 71°C? Explain. A low—boiling or minimum boiling azeotrope is formed between water and cyclohexene. This azeotrope distills as a constant composition mixture at a constant temperature of 71°C. The composition of this mixture will not change with further distillation. 18. (10 pts.) Give the organic product for the following reactions: W H A) H3 3) 5 pts. H3C OH H3 H3 3 pts. H3C \ CH3 ...
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MidtermFall1999Key - Print your name ANSWER KEY 1 Print...

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