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sample_exam_Exam_1_Key - [Cza/ CHEM 241 SAMPLE EXAM #1 1.(5...

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Unformatted text preview: [Cza/ CHEM 241 SAMPLE EXAM #1 1.(5 pts) In the recrystallization lab you cooled the solution from boiling to 0 °C. What would be the consequence of only cooling this solution to 35 °C instead of 0 °C? WV. 074}, (amid. LUCIAch i’l‘L lOWQY~ mg, 74—,» Egg. m ftivn’hfing (Dower Sbiven+ ‘5 Wade“ ’HAW‘ “4. Dace?) 1+ Cam dissatw. MM C6 ‘HA-LSMJJ an”( Wm Luna c{‘H/u1_ Compound will CW“, hawk; 2. (6 pts) What would be the consequence of trying to carry out a recrystallization of a mixture that was 60% compound to be purified and 40% organic impurity? M13 Uw‘ouwflt‘g ‘i‘km’l‘tl‘g Luci-«id GLFSO CVLIJI‘ZJ’)“ along a,th flu, Compound 96M. 1L0 pari‘fy. 3. (6 pts) In the acid base extraction lab, why did you use 6 M NaOH instead of 1M NaOH to neutralized the acid extracts? (TOM mufir 13/44 éMHfiOH +0 Mu’fletan Dad/Ci ’fhcm IMMADHV 3% add-m?) (Mo Kala/4 (101342 may“; W Udium, when ¥o+9w duh-Mall Sfig’l‘ema (MO [Ala-+91 MM Cw,)ao-4,hd€ Cay! p/LeLIij‘a‘b S a tutti m . 4. (6 pts) In the acid/base extraction lab what was the structure of the compound that was isolated when you neutralized the acidic extracts with 6 M NaOH? Questions 5, 6 and 7 refer to compounds A-H below. 0 o o \ H30 W\/OH V\O A CH C ' 3 .5350 LE3 “hp 101 D Cl mp 76 mp 131 Br I j] Q , mpl45 H ,. 1:53 F COZH bp 45 mp 125 mp 185 5. Equal amounts of A, C and H were mixed together and the mixture is distilled. a) (6 pts) What would be the order in which each compound would be distilled over (first, second and third)? Las+ furs"? & K ~——> C. -_> . ‘ A) é buywrl B10 [own 8? b) (8 pts) Circle the gas chromatography trace depicted below which would most likely represent the 1st mL fraction collected from a simple distillation of A,C and H. Tram mum 100K Md 41%;“) \/ H ~1awes+ fel‘ewhm “ +|v‘vu.. —‘? lowest 3? W C. J A , wry/13+ VC’l‘en’héfi +|Mbrqutfl Tlm a 5 c. (8 pts) Draw what the Temp vs Volume graph of this distillation would look like if all 3 compounds (A,C and H) were completely separated. Be sure to denote appropriate temperatures and volumes. Assume that the volume of the original mixture was 30 mL and that there are equal proportions of each compound in the mixture. [6 \Q “’3 I g 10 ml. \lclum/z (ij 6. You have a l:l:l mixture of B, E and G and you will purify this mixture by acid/base extraction. You dissolve all 3 in diethyl ether. You then extract the ether layers 2 times with l M NaOH (you mix then separate from the ether layer). a) (6 pts) Depict the species (draw the chemical structure) that is dissolved in the l M NaOH solution. Mk; I 1L‘ a; 5 ‘06 m9 b)(6 pts) If you wanted to isolate (as a solid) the compound that is dissolved in the l M NaOH solution in 6 a, what would you do next? Add éMHC\ *5 fefwo’l‘O'naftp ’Hu. and \ (OW ’0 Q C) j ) \~\ @ o¢CKOIH ¢¢L\ 9 9.(6 pts) A faulty recrystallization procedure is given below in which there is one procedural error. Point out this error and explain what is wrong with it. Also make the appropriate correction to the procedure. Propanol, h , is added to an impure sample of toluic acid until all of the solid just di olves. The solution is then slowly cooled to 0° C. The solvent is then removed b centrifugation. The boiling point of propanol is 970 C and the melting voluic acid is 1100 C. point of t .4 Shoultfl l/LL at’l‘ Karin/1‘} @453 P m Holler" mauv. FAKE.va (10 .66va [((m Ohm)!“ W as mmdfl b2! \ . l 0 RS SdHAQ—n-t +0 Ambh‘q a” ‘__\ 10. The graphs below show solubility behavior of m-toluic acid and benzophenone in methylene chloride, acetone and ethanol. Use this data to answer a and b. a) (8 pts) Would it be possible to recrystallize a mixture of 85% Toluic acid and 15% Benzophenone using methylene chloride as the solvent? If yes, at what point would the benzophenone be separated from toluic acid (by the filter tip pipet or when the Craig tube is centrifuged?) (amp cc;qu fin Toluic NRA in whast cuts}de ngzspbnam blame). be, Wop/mud Wi— “ELL grant} 31%!) R (Symon) b) (6 pts) What would be the solvent of choice to recrystallize a mixture of 90% Benzophenone and 10% tolulc aCId? a“ “0“ I, 51 mp Cuvwe (methylene chloride methanol - T solubilty (g/mL) __________.__—————-——--—‘ acetone / Graph for m—toluic acid Temp --—-> / A ethanol r _____________.__._—————————- methylene chloride Graph for benzophenone solubilty (g/mL) ____________._.————————-—-“ acetone / Temp 11. Using the solubility data for the solubility of biphenyl in the solvent methanol is shown below. Using this data calculate a and b Temp Solubility (g/mL) 60 °C 0.5 g/ml 50 °C 0.4 g/mL 40 °C 0.3 g/mL 30 °C 0.2 g/mL 20 °C 0.1 g/mL 10 °C 0.04 g/ mL a. (6 pts) How much methanol would be required to dissolve 1.5 g of biphenyl. At 60 °C. at MCI "’5 OBS/“L “53" "w; 3 :fiw‘m‘mol (5.53, b. (6 pts) How much biphenyl would remain in solution if it were cooled to 20 °C? out 100‘; GAS/ML 3 ML (mtg) : 0. '3 gilamc ‘ML 12. (6 pts) What is the difference between precipitation and crystallization? c + Cvnqhhza’mw ” S MN Cool I 347’; Weft—M Cquhd FovMax’hW‘. "/5 (“‘61 10““ g’ PMMP'MhW‘ {0.13364 (Obllha w‘agf-quanl14>VMdgf)’:n ..a\ empwrfieg P 1 I , C . . Va )9 ,0 i VI 13 Draw a flow chart to deplct the separation of F, E and D. Mi H0 3177‘}. ...
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sample_exam_Exam_1_Key - [Cza/ CHEM 241 SAMPLE EXAM #1 1.(5...

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