2015 YJC H2 Chem 2015 Prelim Suggested Answers

8/18/2019 2015 YJC H2 Chem 2015 Prelim Suggested Answers

1/23

2015 JC2 H2 Chemistry 9647 Preliminary Examinations – Suggeste !ns"ers

H2 CHEMISTRY 9647

Pa#er 1$ulti#le Choi%e &uestions

Worked Solutions

1 Sin%e 6'02 × 102(

o) #arti%les is the same asone mole o) the #arti%les

⇒ *ust nee to etermine the num+er o)moles o) the state #arti%les in ea%h %ase

A, 2

12 2 2 1.0

2.0− = × = × = × = H e

mn n mol

M

B, 3 2 1 1 1.0= × = × =CH CO H n c V mol

Ho"e-er. sin%e ethanoi% a%i is a "ea/

a%i.3 2

+ = CH CO H H n n

C, 235.5

0.571.0= = =Cl

mn mol

M

D, 22.4

2 2 2 2.022.42

atoms = × = × = × =m

V n n mol

V

Ans A

2 et the )ormula o) the hyro%ar+on +e C xH y.the euation o) the %om+ustion is there)ore,

2 2 24 2

+ + → + ÷

x y

y yC H x O xCO H O

Sin%e the -olume o) gaseous mixture

e%rease +y (0 %m( "hen it "as #assethrough 3aHa ⇒

2COV (0 %m(

Com#aring the moles ratio to the -olume

ratio o) C xH y "ith that o) C2,

⇒ 2 2= x y x y

CO CO

C H C H

n V

n V . ⇒

30

1 10=

x. ⇒ x (

Sin%e a)ter the %om+ustion the -olume o) themixture e%rease +y 25 %m(.

⇒ ( ) ( )2 2 2

25 rea%te+ − + = x yC H O CO H OV V V V

Su+stituting the /no"n -olumes into theeuation an ta/ing -olume o) H2 at r't'# to+e 0 %m(.

⇒ ( ) ( )2

10 30 0 25 rea%te+ − + =OV

⇒ 2

25 20 rea%te = +OV 45 %m(

Com#aring the moles ratio to the -olume

ratio o) C xH y "ith that o) 2 rea%te. an

su+stituting x ( into the euation,

⇒ 2 2rea%te rea%te=

x y x y

O O

C H C H

n V

n V . ⇒ 454

1 10

+=

y x

.

⇒ 3 4.54

+ = y . ⇒ 4.5 3 1 .54

= − = y

⇒ 1.5 4 6= × = y

Hen%e. the )ormula o) the hyro%ar+on isC(H6'

Ans B

! he euation )or the raioa%ti-e e%ayes%ri+e in the uestion is,

1 1 0

0 1 1+ −→ +n p e

ex#elle )romnu%leus

"here n neutron. p #roton.

an e ele%tron

here)ore. in this )orm o) raioa%ti-e e%ay.the mass num+er o) the nu%lei "ill remainsthe same. "hile the #roton num+er "illin%rease +y one unit'

A, 11 12

6 6→C C . is not a #ro%ess o) this sort

B, 111 111

53 52→ I Te . is not a #ro%ess o) this sort

C, 76 76

35 36→ Br Kr . is a #ro%ess o) this sort

D, 76 75

35 35→ Br Br . is not a #ro%ess o) this sort

Ans C

4 Element E must +e a metal sin%e it has ahigh melting #oint an is a goo %onu%tor o)ele%tri%ity the only ex%e#tion is #ro+a+lygra#hite' he %hlorie o) E must +e a%o-alent %om#oun as it oes not %onu%tele%tri%ity in +oth the soli an molten state.

an is solu+le in a non8#olar sol-ent li/e+enene' 3ote that an ioni% %om#oun "ill+e a+le to %onu%t ele%tri%ity in the moltenstate. an "ill +e insolu+le in +enene'

A, :e is a metal. an :eCl 2 is a sim#le%o-alent %om#oun "hi%h has a#olymeri% stru%ture. an that a%%ounts )ora melting #oint that is higher thannormally ex#e%te o) a sim#le %o-alent%om#oun'

B, Si is a non8metal an it is only a semi8

%onu%tor o) ele%tri%ity. an SiCl 4 is a

sim#le %o-alent %om#oun'

C, Cu is a metal. an CuCl 2 is an ioni%%om#oun'

D, i is a metal. an iCl is an ioni%%om#oun'

Ans A

" he stru%ture o) #otassium %hlorie is thesame as that o) soium %hlorie. "here the%ations an anions are arrange alternatelyin a regular three8imensional array. "here

ea%h ;

<

ion is surroune +y six Cl

=

ions.an ea%h Cl = ion is surroune +y six ;


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%harge #la%e sie8+y8sie in the ioni% latti%e'

Ans B

6 ?hen a metal rea%ts "ith a non8metal. theioni% %om#oun )orme is al"ays the onethat is more sta+le @ that has lo"er energy'

he sta+ility o) CaCl 2s %an +e %om#are"ith CaCl s using the enthal#y %hange o)

)ormation. ∆H ) . -alues' ?e /no" thatCaCl 2s more sta+le +e%ause ∆H ) )orCaCl 2s is more exothermi%'

he -alue o) ∆H ) ACaCl 2sB e#ens on the-arious #ro%esses in the :orn8Ha+er %y%le,

t %an +e seen that ∆H ) "ill +e moreexothermi% i) the magnitue o) theenothermi% #ro%esses atomisation o) theelements an the ionisation o) Ca aresmaller. an the magnitue o) the exothermi%

#ro%esses ele%tron a))inity o) Cl an latti%e

energy are greater'

A, t is not #ossi+le to etermine "hetherenergy is release "hen %hlorie ions are)orme )rom %hlorine mole%ules. as theenthal#y %hange e#ens on the relati-emagnitue o) the +on isso%iation

energy o) the Cl =Cl +on enothermi%an the )irst ele%tron a))inity o) %hlorineexothermi%'

DCl 2g → Cl g → Cl =

here)ore. it is not #ossi+le to etermine

"hether this statement is true or not'B, rue statement'

Sin%e less energy is reuire to ioniseCag to )orm Ca


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% he euation )or the rea%tion +et"een CuS4an ;I is,

2Cu2


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C, Corre#t

$gCl 2 #rou%es a solution that is slightlya%ii% "hen issol-e in "ater. as $g2<

a unergo %ation hyrolysis slightly to#rou%e H


5/23


17 he #ossi+le isomers "ith the )ormula

C2H6=nCl n are,

n iso)ers

1 C

H

H

H

C

H

H

Cl

2 CH

H

C

C

H

H

Cl l

C

H

H

H

C

H

C

Cl

l

( C

H

H

C

C

H

C

Cl

l

l

C

H

H

H

C

C

C

Cl

l

l

4 C

H

C

C

C

H

C

Cl

l

l

l C

H

H

C

C

C

C

Cl

l

l

l

5 C

H

C

C

C

C

C

Cl

l

l

l

l

6 C

C

C

C

C

C

C

Cl

l

l

l

l l

⇒ total num+er o) isomers 9

3ote that there are no stereoisomers#ossi+le

Ans C

1% Oeneral )ormula o) ali#hati% al/anes, CnH2ni%hloroi)luoromethane is %hemi%ally inertas the C= +ons are -ery strong +onenergy

440 /J mol=1'

!s )luorine is -ery ele%tronegati-e. the δ<%harge on the %ar+on atom is uite large i'e'

Page 5 o) 2(

***


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the C= +on is -ery #olar. an so the C8atom shoul +e -ery sus%e#ti+le to atta%/ +ynu%leo#hiles. an so i%hloroi)luoromethaneshoul +e uite rea%ti-e "hi%h is not the%ase'

Ans A

24 n the ex#erimental setu#. one reagent isae )rom a ro##ing )unnel to another inan i%e "ater +ath. i'e' the rea%tion is %arrieout in %ol %onitions'

A, he rea%tion +et"een #henol an :r 2 in

CCl 4 in the %ol "ill ensure thatmonosu+stitution ta/es #la%e' he %ol%onition #re-ents )urther su+stitution o)the #henol'

B, he reagents an %onitions )or the%on-ersion o) ethene to ethanol shoul+e, %ol. %on%entrate H2S4. )ollo"e +y

H2. heat' he rea%tion +et"een ethenean %ol %on%entrate H2S4 "ill only#rou%e the )ollo"ing %om#oun,

C C

HH

H

H

H

S(H

C, he hyrolysis o) 28%hloro#ro#a#ne "ith3aHa to )orm #ro#an828ol reuiresheating or re)lux %onitions'

D, he )ormation o) ester )rom al%ohol an

%ar+oxyli% a%i in the #resen%e o) %'H2S4 %atalyst reuires heating or re)lux%onitions'

Ans A

2" A, :rayNs reagent 2.48>3PH "ill gi-e#ositi-e test )or +oth alehyes an/etones'

B, ehlingNs reagent only gi-es +ri%/ re ##to) Cu2 )or ali#hati% alehye' Hen%e. it"ill gi-e negati-e test )or +oth%om#ouns'

C, 3a gi-es e))er-es%en%e o) H2g "henae to al%ohol. #henol or %ar+oxyli%a%i' Hen%e. it "ill gi-e negati-e test )or+oth %om#ouns'

D, !ueous al/aline ioine "ill gi-e a yello"

##t o) CHI( )or 18#henylethanone +ut no##t )or +enalehye'

Ans D

26 A, *+lsenly the al/ene )un%tional grou# in

%ortisone "ill unergo mil oxiation "ith%ol ilute ;$n4 to )orm a #rou%t "ith 4hyroxyl al%ohol grou#s'

C

CH2H

HCH

(

CH(

H

H

B, *+lseCortisone oes not %ontain the =CCH( or =CHHCH( stru%ture

C, Truehe three /etone )un%tional grou#s in%ortisone "ill unergo reu%tion "ith3a:H4 methanol is the sol-ent to )orm a#rou%t "ith 5 hyroxyl al%ohol grou#s'

C

H

CH2H

HCH

(H

CH(

H

H

D, *+lsehe #rimary al%ohol )un%tional grou# in%ortisone "ill +e oxiise to a %ar+oxyli%a%i. "hile the al/ene )un%tional grou# "illunergo oxiati-e %lea-age "ith hota%ii)ie ;$n4 to )orm a #rou%t "ith 4%ar+onyl grou#s

C

H

CH(

CH(

C2H

C2H

3ote that the tertiary al%ohol %annot +eoxiise. an the C in %ar+oxyli% a%isare not %ar+onyl grou#s'

Ans C

27 Com#oun S #rou%es an orange #re%i#itate"hen ae to 2.4 initro#henylhyraine+ut no #re%i#itate is o+ser-e "hen "arme"ith ollenNs reagent' Hen%e. it must +e a/etone' nly o#tion ! an C ha-e /etone)un%tional grou#'

?hen heate "ith ilute a%ii)ie #otassium

manganateVII. only o#tion ! #rou%esethaneioi% a%i "hi%h %an +e )urtheroxiise to %ar+on ioxie gas "hereaso#tion C "ill #rou%e ethanoi% a%i'

Page 6 o) 2(


7/23


Ans A

2% he )ully #rotonate )orm o) as#arti% a%i is atri+asi% a%i,

>e#rotonation o%%urs "hen the gi-en #H isa+o-e the #K a -alue' !t #H (. e#rotonationonly o%%urs at ① α –C2H "here #K a 2'10'3o e#rotonation o%%urs at ② –C2H at sie

%hain "here #K a ('F6 an at ③ α8aminogrou# "here #K a 9'F2'

Ans C

29 he ty#e o) rea%tion that o%%urs "hen a#rotein is +ro/en o"n into #e#ties anamino a%is is hyrolysis

Ans A

!& Proline #tion > %ontains a se%onaryamine grou#' !)ter )orming #e#tie lin/age.#roline has no more 38H grou# a-aila+le to

)orm hyrogen +on to sta+ilise the #e#tieT8helix'

CH3 C

no H8atom

Ans D

!1 1, Corre#t !t %onstant . a-erage ;'E' remains%onstant

2, Corre#t

# nU ⇒ $r mU@#Sin%e #. an are %onstant.$r S , $r T mS , mT

0'5 g , 2'5 g 1 , 5

!, Wron,Sin%e n #@U an #. an are%onstant. n is %onstant an hen%e no' o)

mole%ules is %onstant )or ' an Y'Ans B

!2 1, Corre#t>issol-ing the solute in the sol-entn%reases the num+er o) "ays o)arranging mole%ules in the solution "hi%h"ill lea to an in%rease in entro#y#ositi-e VS'

2, Corre#t

E-a#oration %auses the sol-ent to %hange)rom liui to gas' his %hange in statein%reases the isorerliness in the system#ositi-e VS'

!, Corre#the mo-ement o) sol-ent mole%ules )romthe #ure sol-ent through the semi8#emea+le mem+rane to the solutionuring osmosis in%reases the num+er o)"ays o) arranging sol-ent mole%ules inthe solution "hi%h "ill lea to an in%reasein entro#y #ositi-e VS'

Ans A

!! ne8 trans)erre 290@96500 ('01 x 10 –( mol

e

M

n x

n x

8(

8(

('01 10 (

11'00 10

−

= =

Hen%e. at the %athoe. $x


8/23


Ans B

!" 1, Corre#t

∆Hhy o) %ation α


9/23


10/23


Pa#er 2Stru%ture &uestions

.uestion 1

/+0 K s# GCa2rain !7"& #)! o) the hyro%hlori%

a%i )rom the +urette into a 2"& #)! olu)etri# l+sk' To:u the -olumetri% )las/ u# to the

mar/ "ith de:ionised ;+ter ' ! the last )e" ro#s o) e8ionise "ater using a ro##er till the

+ottom o) the menis%us %oin%ies "ith the mar/'2' Stoer the -olumetri% )las/ )irmly an in-ert it 10 to 15 times to ensure #o)lete )i


11/23


/d0/i0 310M 3 HCl n mol −= × ×

2

3

( )

1 110

2 2M 3Ca OH HCl n n mol

−= × = × × ×

⇒ 3

3

2 1 3

110

12[ ( ) ]25.0 10 50

M 3M3

FACa OH mol dm

−

−

−

× × ×= =

×

/ii0Sin%e

3

2 1

1[ ( ) ]

50M3

FACa OH mol dm−= .

⇒ 2 31

[ ]50M3Ca mol dm+ −= an 3

1 1[ ] 2

50 25M3 M3OH mol dm− −= × =

⇒ K s# 2

2 2 5 3 3 3 91 1[ ][ ] 3.2 1050 25

M3 M3 M 3Ca OH mol dm+ − − − = = × ÷ ÷

/e0 :oth HCl an CaH2 are #orrosie We+r ,loes = ut on + l+or+tor3 #o+t = ut on,o,,les = use + droer "hen hanling the %hemi%als

r HCl is to Aer+,e M+rk 6% /42"?0

/+0 %hemi%al #arameters a-erage reaing @ mg m−( a-erage reaing @ mol m−(

Cl 2a 2'( ('24 x 10−5

3H2Cl a 2'0 ('FF x 10−5

P4(− 0'012 1'26 x 10−7

e as e2


12/23


/#0 or #re%i#itation to o%%ur. & Z K s#

GCa2


13/23


/ii0 !l


14/23


/ii0K c =

2 3

2

3

[ ][ ]

[ ]

NO NO

HNO

+ −

= 2 2[0.1][0.1] 0.01

90.3[0.05 0.2105] 0.0105

= =×

(no units)

/iii0 32< "ill unergo ele#tro5ili# sustitution "ith the +enene ring o) #henol to )orm nitro#henol'

!s a result G$2F ;ill de#re+se.

:y e ChatelierNs #rin%i#le. the #osition o) euili+rium "ill shi)t to in%rease the G3 2 Aer+,e M+rk 7" /"&&?0

/+0reagent

%om#ounW. '. Y or (

stru%tural )ormula o) the organi% #rou%ts

P:r ( W:r

2.48initro8#henylhyraine '

3 3

H

32

23

Page 14 o) 2(


15/23


ehlingNsreagent.

heat'

8

a%ii)ie;2Cr 27a.

heatW

/0/i0 ele%tro#hili% aition

/ii0 6

/iii0 28methyl828#henyl+utanoi% a%i

/i0

C

CH2CH

(

C2H

CH(

C

CH2CH

(

C2H

CH(

mirror #lane

/#0

C C

s#2 hy+riise

#8or+itals

s#2 hy+ri or+itals

Page 15 o) 2(


16/23


Pa#er (ree Ues#onse &uestions

.uestion 1 @

/+0/i0 ! "ea/ a%i is one that disso#i+tes +rti+ll3 to don+te H ions

/ii0 Sin%e #H 1'44

1.44 2 3[ ] 10 3.63 10 H moldm+ − − −= = ×

2 2 23 3

1 2

[ ] (3.63 10 )8.05 10

[ ] 0.20 3.63 10a

acid

H K moldm

c H

+ −− −

+ −

×= = = ×

− − ×r

2 2 23 3

1

[ ] (3.63 10 )6.59 10

0.20a

acid

H K moldm

c

+ −− −×= = = ×

/iii0 ?hen a small amount o) a%i is ae.

S(2=

< H<

→ HS(=

?hen a small amount o) +ase is ae.

HS(= < H= → S(2= < H2

/i0 he anion o) the salt )orme at the se%on eui-alen%e #oint. S (2=. is a "ea/ +ase. an

unergoes hyrolysis in "ater to #rou%e H='Hen%e' #H at #oint C is greater than 7'S(

2= < H2 ⇌ HS(= < H=

/0 :oth leum an sul)uri% a%i ha-e sim#le mole%ular stru%ture an they are hel +y hyrogen+oning +et"een their res#e%ti-e mole%ules'leum has mu%h more ele%trons than sul)uri% a%i an hen%e has stronger instantaneous i#ole –inu%e i#ole i8i attra%tion than sul)uri% a%i'

re heat energy is reuire to o-er%ome the stronger i8i attra%tion in oleum⇒ higher melting #oint

/#0/i0 Stanar enthal#y %hange o) neutralisation is the 5e+t #5+n,e "hen one )ole o ;+ter isor)ed "hen an a%i neutralises a +ase uner stanar %onitions o) 29% G +nd 1 +t)'

/ii0 CH(SH < 3aH → CH(S=3a


17/23

δ+


/ii0 Ste# , %ol. %on%entrate H2S4. )ollo"e +y heating "ith H2Ste# , ;$n4 or ;2Cr 27. H2S4/+0. re)luxSte# , H2S4/+0. re)luxSte# , CH(CH2H. %on%entrate H2S4. re)lux

/iii0 3u%leo#hili% !ition

3aC3 → 3a


18/23


/e0 CH

3H(<

H

CHCH2

3H2

-

CH2CH2H

3H2

TCH2CH

3H(<

S

3H

CH2C

R

$ M G

• 28nitro+enene unergoes redu#tion "ith Sn in %on%entrate HCl to gi-e .28amino+enoi% a%i' he amino grou# is #rotonate uner the a%ii% %onitions'

• $ is a ter)in+l +lkene as it unergoes o


19/23


C

3

CC

C

C3

H

C

H

C HH

C

H

C

3 C

H

C

H

C HH

C

H H H

H

HH

H

H

H

/iii0

/0/i0 he !uaternar" structure o) a #rotein is the asso%iation o) )ore t5+n one ol3etide #5+ins to)orm a t5ree:di)ension+l stru#ture that %on)ers the +iologi%al )un%tion to the #rotein' hestru%ture is sta+ilise +y inst+nt+neous diole : indu#ed diole inter+#tions et;een non:ol+r R:,rous> 53dro,en onds et;een ol+r un#5+r,ed R:,rous> ioni# inter+#tionset;een oositel3 #5+r,ed R:,rous +nd disul5ide link+,es et;een @SH ,rous o t;o

#3steine residues' Haemoglo+in %onsists o) 4 #oly#e#tie %hains. 2 :suunits +nd 2 J:suunits "hi%h are "oun to gi-e a s#heri%al sha#e' Ea%h #oly#e#tie %hain is linked non:#o+lentl3 to a 5+e) ,rou #ont+inin, *e2 ion'

/ii0 aline %ontains a non:ol+r +lk3l ,rou that )orms inst+nt+neous diole : indu#ed dioleinter+#tions "hile glutami% a%i %ontains a ne,+tiel3 #5+r,ed @C ,rou /+t H K 70 that)orms ioni# inter+#tions'he hyro#ho+i% sie8%hain o) -aline is a+le to inter+#t ;it5 t5e non:ol+r +t#5 on t5e sur+#eo +not5er 5+e)o,loin )ole#ule. %ausing the haemoglo+in mole%ules to aggregate'

/#0/i0 CH

CH

CH

C3H2

8 .

/ii0 Ste# I, CH(2CHCl . anhyrous !l Cl (Ste# I, Con%entrate 3H( or 3H(g. room tem#erature in a seale tu+e

/iii0 Ueagent, ;$n4 "ith ilute H2S4 an heat+ser-ations, Pur#le ;$n4 e%olourise "ith methyl+eneneY ;$n4 remains #ur#le "ith P!:!'

r

Ueagent, :r 2a+ser-ations, Ueish +ro"n :r 2 e%olourise "ith methyl+eneneY :r 2 remains reish +ro"n"ith P!:!'

Page 19 o) 2(

+

+

−

..

Hyrogen +on

−


20/23


r

Ueagent, 3a @ 3a2C(+ser-ations, E))er-es%en%e o) C2@H2 )orme "ith P!:!. "hi%h )orms a "hite ##t "ithlime"ater@extinguishes a lighte s#lint "ith a M#o#N sounY no e))er-es%en%e "ith methyl+enene'

r

Ueagent, PCl 5 or SCl 2. anhyrous

+ser-ations, ?hite )umes o) HCl )orme "ith P!:!Y no "hite )umes "ith methyl+enene'

/d0/i0 e < 2HCl → eCl 2 < H2Sn < 2HCl → SnCl 2 < H2

/ii0 o #re%i#itate out e2


21/23


PT = P

N2O +P

N2

+PO2

total #ressure. & 25'0 = x < ' x


22/23


/ii0

.uestion "

/+0/i0 Cl 2a < H22a → 2Cl =a < 2H


23/23


#H =log F'29 _ 10=( 2'0F#H 14 – 2'0F 11'9

/d0 High tem#erature !t high tem#erature. the gas #arti%les #ossess high /ineti% energy su%h that they ha-e su))i%ientenergy to o-er%ome the intermole%ular )or%es o) attra%tions +et"een them' Hen%e. theintermole%ular )or%es +et"een the gas #arti%les are insigni)i%ant an negligi+le'

o" #ressure !t lo" #ressure. the gas #arti%les are )ar a#art )rom one another an so they ha-e negligi+le-olume as %om#are to the -olume o) the %ontainer' n aition. the intermole%ular attra%tions+et"een the gas #arti%les are also insigni)i%ant an negligi+le sin%e they are -ery )ar a#art'

En o) Suggeste !ns"ers

Documents

2015 YJC H2 Chem 2015 Prelim Suggested Answers