Document 6539240

Chem 251 sample exam #2
For questions 1,2 and 3: refer to compounds A-I1 shown below
G
You h a w a mixture of: B, C and D. Use a flow chart to show how you could isolate and
purify trll 3 of'these components. Show Ihc structures that a r c h each la~rcrof the
separation. (You do not need to denote the amonnts of solvents used)
Circle all that arc =regarding
chrornatograpl:y.
a. In our chromatography lab the station:l~-yphase was Ihedevcloping solvent.
b. A pollzr solvent will only increase the Rf \ralue of' polar compounds (and not nonpolar)
c. When using a polar dc\lclopi~igsolvcnt. polar con~poundswill
T1,C plate.
move up the
d. A carboxylic acid will have a smaller R f \ialuc in hexanc than in methanol
c. 111 Chromatography the mobile phase is tlic solvenl.
g. In '1'1,C' \\hen you increase thc polarity oi'the Jevcloping sol\,cnt all coinpomds
(polar and non-polar) will increase thcii resl~cctivcR1'values.
Draw the reaction n~echanisn~
and products for :he ;ilcohol dehydration reaction
shwvn belo\?;.
b) (4 pts)fTorthe reaction abo\!c, is sulf~~ric
acid (t12S04)considered 3 catalys!:' (yes or
no)
c) (4 pts) ]:or thc reuciion above, ho\v coi~ldyou ensure t11atthe reaction ccluilibrium i~
shilled lo the right (Ibrrnalio~lof the products).
d ) (4 pts) /it thc c ~ of
~ ~d h cspcriment
c
c'll>ove,sodium sulfate is added to thc product.
Wliat is [lie purpo:ie 01' tl~is'?
c) (6 171s) For the 1,eaction abovc, if you stai-lcd with 2.5 g of alcohol whal ~ z o ~ be
~ lthc
d %
yield if you isolated 1 :I g of thc organic product.
1-or questions 1 and 2, rci'er to compounds A-I I shown below.
F
F
1. a)(J pts) Which compounds above (A-II) woi11d bc soluble in 1 M NaOIi'?
b) (4 pts)tIrau the chClnical stl.Licturtf of !he colnpound(s) rhat \vould bc dissolved in 1 b1
NaOtl.
2. a)(4 pts) Which con~poundsabove (/?-I I ) \rould bc sol!~blcin 1 M fl(ll'!
I>) (0 pts)l)rav, thc chemical structure o:'the ~r)!~:po~~rrd(s)_that
would be ~lissol\~t.d
in 1 M
11CI.
3. Y o u lia\fca mi\turc or I>, 1: and <;. and yo11 will anai!,~cd this mixture bc 1'1 C'.
i'l,(' piate dc\~cloj>cdin acetone is shown belov: (the leli vdc 'l'l,C' plate).
acetone
I lle
ethanol
a. ( 5 pts) Assign the ic!entity ol'cach spot (I). 1; ancl (3) on the acctonc I1,C plate
b. ( 4 pts) Rank tile I-clativc s i ~ of
e the Rf vali~esfor 11, 1' and
(;.
(largest to smallest)
c. (4 ptsj In thc space pro\,idcd above, sltctch what the 'I'I,C' plate might look likc il'it had
been tlcvclopcd in I lesanc instead of acctonc (be sure to label \chich spot is which)
d.(4 pts) In the space pro\,idcd abol'e. sketch what the 'I'1.C plate might look likc il'it had
been developed in ethanol instead of acetone (b:: sure to Iribcl uhich spot it whicll)
4. (13- pts) Yo11hakc: a mistirrc oSE, I: and G . Note the 94ol'cacli compound i n the
mistu~.c.llsc a Ilow chart (as you did f'or expcrirncnt # 5 5 ) to show h o ~ cyou could isolate
and purify 2 of these components. s o w the structures that are in cacl~Iaycr oStlle
separation. (Yo11do pot need to denote the crt?iorlv/.\ of sol vents ~ ~ s c d )
6. A reaction showing thc co~lversionof some vegetable oil to Biodiesel is shown below
0
C
O
O
vcgctablc oil
a. (3 pts) 1 low many dii'fercnt biodiescl molecules woi~ldthis rcaciion produce?
b. (4 p!s) Jlra~vthe structl~reol' o,7c1 of the biodicscl molecules that would bc produccd
c (3 pts) Ilraw thc structure ofglyccrinc
Q L I C S ~ ~7-1
O I -I4 Sperlain to the temperature vs volrrn~egraphs shoivn below
Distillation #2
1)istillation #1
Volunie (nil,)
Volumc (ml,)
7. (3 pts) Which distillation ( k l or # 2 ) ~ v a s11iosLlikely a simple distillation'!
8. ( 3 pts) Which distillation (if any) acliicvcd separation of thc two licluids?
9. (3 pts) \.\'hicli distillation (#I or #2) had morc 'l'hcoretical plates'.
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Question 1 1 -13 reltr to the distillation graphs ~lbnve.
1 1 . (3 pts) Which gas chromatography !race bciow (a-d) illat would most likcly reflect 11ic
2"d ml, li:~c~io:i
ofclistillation # l ?
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12. (3 p ~ s 'Jdllich
)
gas chrolnatography trace bclon (a-d) Illat uould most likcly rcflcct thc
1n1, ]';action of distillation #2'! ---
.,lid
,
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13. ( 3 p l y ) Wliich gas chromatography I~-acebelow (a-d) that woi~ldmost likely rellect the
8''' ml. !raction of distillation # l :' --- -
14. (3 pts) \Vliich gas chromatography trace bclow (a-d) that ~ n i ~ niost
l d lihcly rcllcct tlic
8''' ml, Sraction ol'distillatiun #3?
.
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Chem 251 sample csam #2
ihy
t o r clucs:ions 1.2 and 3. r e t r ro compotinds tj.-ll shni+*nbelow.
You have a r n i s l u l . ~ol': H. C and D. Ilsc a llou chart to shon how you coulci isolate and
purify (:I1 3 ol'lhcsc components. Show the structures that arc i11 each layer ol'll~e
scpx-dtion. ( Y ~ do
L not necd to denotc t h amounts
~
of solvents iised)
a. In our cliro~natogr;ipliylab the s~a1ic)narqphase \vas the dci'clopinz sol\,ent.
b. r\ polar soivent kill only increase tlie Ri'vali~e01'1:olar compounds (iind r,ot nonpolar)
c. When using a p ~ l a tlcvcloping
r
solvent, polar compounds will
'1'1,C' plate.
4 carboxylic acid nil1 have a sm;~llerIIF value
B
ill
not move LIPthe
llesanc than in r1ict1i;inol.
@In Chromatography the mobile plia:;c is the sulvciit.
Q
g. 111'1'1,C when you increasc the polarity ol'the cle\~c!opingsolvent all c o ! ~ ~ p o t n ~ d s
polar and non-polar) will increase their rcspcctive Rf vali~cs.
I>l-a\vthc reaction incchanism and IJI.OC!LIC~S
i?)r the alcohol dehydration reaction
b ) (4pts)lfor the rcaction a b o ~ t .is
. s \ ~ l i i ~ racid
i c ( 1 12SOl)considered a catalqst'!
no)
i i r tq*ct8
c ) ( I PIS)I'or the reaction a b o ~ e hoit
.
collici 101: ellsure that the rcactiol~ccluiilbriuin is
hhilicd to the right ( li)rn~atioiiol'thc. prod ucls).
e ) (6 pls) For thc rcaclion abovc. il'you stiirtcd \vith 2.5 g of alcohol \vhat \vo~!ldbc the O/o
yield if you isolaled 1.4 g of thc organic product.
2.3j --1 )
r n d k
o-o\+sw&,d\,.h.\
1721
--+
0.01% m o b
4 i l 6ptct,
~
l.'or questions 1 and 2, rcfcr to coinpoiti?&; A-11 shown bclo\v.
:L
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3
F
1. a)(4 p!s) Wl!icll compounds xbokc (A-'t1 ) wot:ld be solitblc in 1 hl r\iaOl I*!
Ac
a
2 2
o \ ~
?L.L3
E,
G
b) ( 4 pts)l)rau 1t1echcmical struct~~re
of the con~pound(:i)that would be dissol\,ed in 1 M
NnOl I .
@ U k bJ
EJ
L'
11
0
I
f?
,,\
,J0 4 @
/5yc
-7'
@
A ~ oI r 2 0 ,
I
oH ~ ~ r o t m a b d
E'
Mu
2. a)(4 ptsj !M1Ilich colnpo~lndsabove (A-11) would be soluble in 1 M IIC'I'?
14
A
I
~
G ~ k t bG-delok h a t -
~aluh~.
3. You II;LL'C il niisti~reol' I), F and (;. and y o u \ k i l l analy~cdthis mixture b;, 'I'LC. 'I'he
'I'LC plate dc~clopcciin acetone is sho\vn bclo~v(the left sidc '1'1,C plate).
acetone
ethanol
liesanc
a. ( 5 pts) Assign the identity of each spot (D, I: and G ) o n thc acctonc .1'1.C plat<,:
b. (4 pts) [tank t l ~ crelative s i x of the Rfvalucs for D. 1.' :ind
(;.
(largcst to smallest)
c. (4 pts) In the space providcd abovc, sketch what thc l'l.C platc might look like il'it had
been d c \ ~ l o p c din 1 Icxane instead of acetone (be sirrc to label which spot is \ \ hich)
d.(4 pts) In thc space provided above, sketch \+:hatthe '1'1,C plate might look like i l ' i t had
been dcvclopcd in ethanol instcad oi'acctsne (be sure to label which spot it which)
4. (!2 pts) Yo11! ~ n \ ca niisti~rcol'k. 1: 2nd Ci. %ole!he %I of'cacli compocnd in rhc
misturc. llsc u ilow ::hart. (as you did lbr espcri~ncntit5.5) to show how you coiild isolate
and purify 2 ol'thcsc componcnls. Show the strilcti~rcsthat are iu tach laycr ol'thc
se1);1r:1Iion.(E'OLI
do not rlccd to denote the nr~ro:~n/.s
of solvents L I S C ~ )
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6. A rc:lction sliobing tllc conversion oi'some \c.getablc oil to Hiodiesel is shown below
0
<0&---4-
x.egetablc oil
a. (3 p:s)
110\1
Illilll\' dil'fcrcnt biodicsel ~ ~ ~ o l e c ibould
~ l c s this rcaction product"
6
5. (4 pls) lIl.a\t llie strrlcturc ol'or~eol'tllc biodicscl n~ulcculcsthat woi~ldbe p~.oduccd
c ( 3 pts) Draw tlic slrucli~reof glyccrinc
1
Questions 7- 13 pertain lo the tcmpcraturc vs volarnc gl-al~lissho\vn bclow.
l'olurnc (n-11,)
Voliin~c(ml.)
7. ( 3 ptr) Wlricll distillation ( # l or #?) was most likely a simple ilist~ll;~tiorl'!
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8. (3 pts) Which distillation (if any) achie~rcdscpsration of the t\+o liqi~iils'?
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'9. ( 3 pts) \\'hich distillation ( K 1 or #2) l ~ a dmart' ' 1 heoretical
ol,lr~\'.
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Qucstion 1 1-14 refi'l. to the distillatio~igraphs ~:bovc.
I 1 . (3 pts) Which gas chrl~n~atography
!race bclo1,v (a-cl) that \\oi~lciIIIU!,~ l~hclyrl:llcct tllc
.,"'I mL, li.:rction of clistillation #I '?
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12. ( 3 pth) Which gas chromatography tract belo\\ (;I-(1) that \\nilld n w t libilv ~ e l l c c tthc
,,, rnlJ 1';action ol'disrillation #2:'
ll~!
b
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13. (!I pis) Which 62s chromalography tract. bclow (a-d) that uo~tlclmost I i h c l ~~ctlcct~ l l c
8"' 1111~traction of distil1,ltion ti 1 ? -C
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14. (:ipts) Wllich gas chromatography trace bclow (a-d'r that t ~ o i ~ most
l d libcly ~'cllcctlllc
8"' nl!, fraction of distillation #2? - - -- - -
d
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