CHEM 251 sample exam (summer)

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Phillip Jacobs
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1 HEM 251 sample exam (summer) 1.a (15 pts) ircle the pairs of compounds below that would be miscible (soluble) with each other. H H H 2 H H H 3 H 2 H 2 H 2 H 2 H 3 H 3 H 2 H 3 H H 3 H 3 H 3 H 2 N NH 2 b (6 pts) Rank the compounds (A-E) below in order of solubility/miscibility in hexane (1=most soluble 5=least soluble) H H 3 H 3 H 2 H 2 H 3 H 3 H 2 H 2 H H 3 A H 3 B D E Rank c. (3 pts) which compound(s) above would be soluble in water?

2 2. (4 pts) 100 mg of sulfanilamide is dissolved into 15 ml of water. Which, sulfanilamide or water, is considered the solute? 3. In PLKE experiment #4 part D extraction you used diethyl ether and 1 M Na to extract out the benzoic acid impurity from your unknown. a) (4 pts) What was the compound that precipitated from solution when you added 6 M Hl to the Na extracts? b) (4 pts) ould you have used the solvent methanol instead of diethyl ether in this extraction (assume that you both your unknown and the acid impurity are soluble in methanol). If not briefly explain why. 4. Using the solubility data for the solubility of sulfanilamide in the solvent methanol (boiling point 60 ) is shown below. Using this data calculate questions a-d below. Temp Solubility (g/ml) 60 o 1.5 g/ml 50 o 1.2 g/ml 40 o 0.8 g/ml 30 o 0.4 g/ml 20 o 0.1 g/ml 10 o 0.04 g/ ml a. (4 pts) How much methanol would be required to dissolve 3.0 g of Sulfanilamide at 60 o. b. (4 pts) How much sulfanilamide would crystallize if the solution were cooled to 10 o c. (4 pts) If you wanted to recrystallize 4.5 g of sulfanilamide, how much methanol would you need?

3 5. (4 pts) Why is it important to cool the solution slowly during crystallization? 6. (5 pts) In the solubility lab (PLKE #2), explain why ethyl 4 aminobenzoate was not soluble in water but that it was soluble in 1M Hl? H 2 N H 3 H 3 ethyl-4-aminobenzoate For question 8 a-d, refer to compound A shown below. H 3 A 7.You dissolve 0.25 grams of A in 2 ml of methylene chloride (H 2 l 2 ). You add 5 ml of 1 M Na and shake. You let the layers separate and you evaporate the methylene chloride layer and you find it contains 0.05 g of A. a) (4 pts) Draw the structure of the compound that is dissolved in the 1 M Na layer. b) (4 pts) If this mixture was extracted with water instead of 1M Na, how much of A would you find in the methylene chloride layer: (circle one of the 3 answers) 1) less than 0.05 g, 2) 0.05g or 3) more than 0.05 g. 8. (4 pts) Which compound, or D, would have the largest distribution coefficient (K) between methanol and hexane? (Assume the Hexane solubility term is in the denominator/bottom). H 3 H 3 D

4 9. Shown below are two graphs showing solubility vs temperature. The upper graph is the solubility of m-toluic acid in 3 solvents; methylene chloride, acetone and ethanol. The bottom graph shows the solubility behavior of benzophenone in methylene chloride, acetone and ethanol. Use these graphs to answer a, b and c. a) (4 pts) List the solvent(s) that you could use to recrystallize m-toluic acid. b) (4 pts) For Benzophenone, for which solvent could you say that it was soluble hot and insoluble cold? c) (4 pts) For Benzophenone, for which solvent could you say that it was insoluble hot % userdict/chemdict L/gr/grestore L/tr/transform xl pp l SA RA}{6-1 st}b/ra{py -8 np gs fill e o cp 5 a wy dp 0 In [1 [0 and w 0 cw -1 bw dp/cy -2 2 hemdraw opyright sc p I cm fill pp}{sqrt 0 pa -1 m2 ix o DA}{cw p 2 dv t insoluble l r lt{ mv 3719 sc -1 exec}{al o 4940 px cm 2 sm a}b/pt{8 0 gr}{pp}{gs 4 HA}{dL dv s{dp g mv o dv r x -.6 sc 32 WI b2 12 sm 0-1 A xl neg lp np t 0 mv n LB wf at sc bd a}{ex -9.6 p 7 st px L/gs/gsave e neg mv 1 L/xl/translate cold? Laser A}{1 p 7 arcn 1986, 40 clip}b/t{bs np l -1 p al neg}if/py m 1180 l mv B cp at st}b/ha{lw r wy o mv DSt px ro n s l np fill st}{0 n/ex Prep lp counttomark{bs ac sg 1 ix ar bw e dp SA wx 1987, -1 ro B/bL bd 0.6 sc 7 dict rad ac [2 px gr 3320]B 871]B 947]B 2257]B 7061]B 4915]B 4687]B 5998]B cv 1 fill 8 al 1 sc m1 DLB -1 x L/ie/ifelse 0 dp eq{dd}{ds}ie at DA}{dL n p 3 end}b/db{bs{dp SA py Ar 08 ey gr 120 bd ne{bw put sc r py l dp I L/S{sf mt rot m chemdict ambridge rad gr s -1 px x mv 2168 l}for cm r DA}{cw -1 n/ey m/w e p b1 ro py g A 5180 l 0 ac dv lt{-1 sm tr/dy ac -.6 aa a}ie}b/ww{gs a}ie}b/bw{wd dp p m}b/da{[3 0 st 2 x 871 L/ix/index py sc px 0 A}{1 8 l -8 st}{asc p rot np dv}{bd}ie 6 gr}{gs dx 2.2 s 0 m ne{bw cp begin DLB 1 SA g 0 53 py x/dx 24.6 DSt Scientific a g 0 sc n/dx l m -1 begin/version cm lp r sqrt DA}{dL neg}if/px sl mv type[]type -1 r 012 p [4 sm arc SP ac LB x -4.8 s 180 o py 2.25 x e S]}b/dL{dA sc dp mv L/l/lineto I 0 al B dv/bd B st}{0 gs r 5 wf ac dy lw eq{db}{ds}ie 90 p cw py 25.8 wd pp rev{neg}if 6-1 omputing, w sg 16 r ac l SA B n/dy m 1-1 e A r -2 lp sg SA o x r px begin fill sc dv cw 0 eq{dp x}if r m 2257 Ar DA}{cw cv cx p np[{py dv 1 sg py 24 e 0 fill s 16 L/mt/matrix A}{1 bs DA}{2.25 x 0 setgray arc 2737 p wy -1.6 a fill mv cm rlineto lp def/b{bind lx 0 e 1 bw cm bs p sc}b/v{ra DSt gs 0 g/wb cp p 1 o ac ly wx e sm cm 0 l 27 Inc. 16 r g e mv sm 5 ac cy w n pp}{2 3 cm 0 px py gs g [5 2 clippath st sm m p cp 21.6 ac neg lw ne{bw cm div st}{asc 2 x 1 eq{gs SA sm lp px cm mt I WI gr}b/b{/bs sl l m L/mv/moveto bs fill}b/sa{af sm m or{4 def}bind w dup e 4 0 ro gi st}{px py sm 4883 A}{1.5 p bl e neg put gi 0 st}]e dp 4.8 l tr al g/bb ZLB AA}{1 2 p r 0996 gs py cp l 12 al wy cpt dv/bd pp rad 0.4 r S 7061 ac pp -1 DA}{270 lw 39 r xl}{xl setdash}d/cr p 4 gs x lt{pp a/py 14 o cm e setgray np def/l{load w px -1 sc 1 ap SA m wb DT}]o at ac x end -1 o s L/m/mul p r}if Ar x}if sm}b/b{np[{[{s}{s eq{dl}if cv -0.4 dv g 0 sc DSt 3 xl py mv ro}ie}b/aa{np cp sc lw x A}{1 42 pp exec 0 ix rad gr}b/in{px 763 ZLB 8 sg 4 pp wx round 180 g/cx S}if/lp st}{1.0 1 a Bd [ m/al 3 A -1 pp}ifelse py lw fill 1 0 w g a/px ix gr}ie}b/r{0 0 I 1118 L/n/neg r gs def}b/d/def gr}b/wd nh 360 p AA}{ n SA g 612 DA}{180 x 3 r sc -2 xl o/cx 9.6 ap 1 exec}b/s{p 4 x wb -1 Ac}{0.5 LB cm o dv ac al d/wf 3 A}{1 l sg arc gi lp l 763 s{nh gs w dx o e px s/wx 1 p al gs 0-1 fill rad L/np/ne lt{e}if cm n g/cy cx r dp/cy ar ne{py mv p pp e m s sc 1 S st}{0 A gr dv 9.6 L/a/ mv -1 n 360 dic Ac} 0 DS x sg dv w 212 r ra cm 0 1x m ps dg n methy len e ch lo ride eth an ol so lu bilty (g /ml) aceto n e Gra ph fo r m-toluic a cid Temp eth an ol methy len e ch lo ride so lu bilty (g /ml) aceto n e Gra ph fo r benzo phenone Temp

5 10. (8 pts) You have the mixture of A and B below. You want to isolate and purify both A and B from this mixture. You first dissolve the mixture in ether. Fill in the flow chart below to show the rest of the purification. Be sure to draw the structures that are in each layer of the separation. NH 2 H 3 l A H 3 B 11. ircle all that are true regarding chromatography. a. In our chromatography lab the stationary phase was the developing solvent. b. A polar solvent will only increase the Rf value of polar compounds (and not nonpolar) c. When using a polar developing solvent, polar compounds will not move up the TL plate. d. A carboxylic acid will have a smaller Rf value in hexane than in methanol. e. In hromatography the mobile phase is the solvent.

6 12. You have a mixture of D, F and G. and you will analyzed this mixture by TL. The TL plate developed in acetone is shown below (the left side TL plate). H 3 H 3 G D l F acetone ethanol hexane a. (5 pts) Assign the identity of each spot (D, F and G) on the acetone TL plate b. (4 pts) Rank the relative size of the Rf values for D, F and G. (largest to smallest) c. (4 pts) In the space provided above, sketch what the TL plate might look like if it had been developed in Hexane instead of acetone (be sure to label which spot is which) d.(4 pts) In the space provided above, sketch what the TL plate might look like if it had been developed in ethanol instead of acetone (be sure to label which spot it which)

Experiment 1 SOLUBILITY. TIME ESTIMATE: Parts A-D (3 hours); Part E (1 hour); Part F (1 hour) CHEMICALS AND SUPPLIES PER 10 STUDENTS:

Experiment 1 SOLUBILITY. TIME ESTIMATE: Parts A-D (3 hours); Part E (1 hour); Part F (1 hour) CHEMICALS AND SUPPLIES PER 10 STUDENTS: Experiment 1 SOLUBILITY TIME ESTIMATE: Parts A-D (3 hours); Part E (1 hour); Part F (1 hour) CHEMICALS AND SUPPLIES PER 10 STUDENTS: Part A Benzophenone (Grind up the flakes into a powder) Malonic acid