Cape Chemistry 2015 U2 p2 Ms

 

022].2020/CAPE/MS 2015

CARTBBEAN

EXAMINATTONS

COUNCII,

CARIBBEAI{ ADVANCED PROFICIENCY EXAMINATION@

CHEMTSTRY

UNIT2_PAPER02 MARK SCIIEME MAY/.TUNE 2O].5

g

 

a'.. ::"

'. ..

l,-

.

lr

...\'1::;:

1,r,1.,i...;,:

r',l..ii:lf

'

r.,i::.:,:$ 'r:rt'-1,:i,1

..." ::.;i

,$

.:;,

-z-

.j:l

o

CIIEMISTRY

22L2O2O / QAEE h"rs / 20 Ls

UNTT2-PAPER02 MARK SCHEME

Question

1

Specif,ic objectives: Module: 1 _ l.L, 2-5, 2.3, 2.4, 2.s

(a) (i) (ii

cracking )

KC

(1)

vapour passed over cataTyst/ A1zO3/SiOz at 450 oC (1)

I'K xsi

2

OR

Thermal Cracking high temperature (>600"C)

(iii)

B: methane, cHa c: propene,

NOBE:

b) (i)

(1)

CHsCH

=

CH2

(1)/

2

CH:cgcgz

condensed must be products ttre are both foruriI.aei ft gases and can be either girrea aCg o There is the unpairinq of (Ll 2sz electronsor(orc tion o 2s2 to the orbi and e.l-ectron en ters the empt P orbi-tal o The f, taLs sed ve4 (1) orbitals

(ii1 B.o*ine with propane in sunlight Iaitiation:

a1;Gr

----D

Br. + Br.

Ensure fish hook arrow is stroytr

Propagation

EE

tr E

I

c I

E

(1)

"E + .'Ar Irt-C l^,'-^

EE

I

v

EEf,

tll

tr-c-c-c.

ltl

+ E:Br

EEE

(1)

BEX

tlt

E-c-c

ltt

EEE

-c {_gr.: ar

ltl+

(11

IIEEI

*

-C-C:Br ttl EEE

+.Br

2

:::\

 

-3o

CHEMISTRY

22L2O2O /CAPB /MS /2

UNIT2-PAPER02 ITIARK SCHEME

stion

1

.

cont, d .

frro etepa ate r€quLred in tlle ptopagatiolr stage, if -^ two steps are present and no tisn hook i..o* f..ri-' o If one of j.s no marks   missing the twoallotted steps missing and fish hook is

Ieraiuation: .Br + .Br Br3Br -.. E EE

lt c

I

2a-g-

-c. tt EE

I

E

I

I

E

OR

f,

-+

tt -c-c tt EE

EE

E

a-c

EE

lt

tttt

c-c-c

ltlt

EEES EEE

ttt

- tt-c. 'i.st c

E

-c-

1)

R-C-C-C-Br

ltt

EE

ETE Any ONE to receive 1 narh

bromine with propene (without sunlight)

EE

tt E-c-c-c

E

I

+ Br:/\Br

E

E

fu.LI arrors and not FISE EOOR (1)

E

tt

E

E-C I -C

c

+

+

lt

I

E

E-c-c-

I

tt

c

+

f,

EBT

I

c I

E

:Br' (1)

E

E

A]1 anrors

l

E

G

EEEE

+

Br(1)

EEI

ttt

-c -c -E

tt

Br

Ba

(1)

shouJ.d be

O

15

 

-4-

o

22L2O2O / CAPE /t{S /2

o1

s

CHEMISTRY

UNIT2_PAPER02 MARK SCHEME

OR

ll,/ H-C-C-c UE

B

r

1r

E

E

I

I

c I

-c

E

+ I

c

+

I

UE

(1)

steps can'be merfed with the appropriate arrow, one mark for

I

c

+

T

E

I

I

I

I

+ E

+

Br-

(1)

Br

u

E

 ,

the direction of each arrow

E

H-C-C

c

:Br-

E

Br

The two first

ll ll

(1)

n

E

E

Br

c

c I

r

I

Br

B

I (1)

 

-5-

o

CHEMISTRY

22L2O2O / CAPE /MS /

201

s

UNIT2-PAPER02 MARK SCHEME

Ouestion 1 cont'd KC

(iii)

Free radi.caL substitution OR

Electrophilic addition, (c) (i) ii)

(1)

xs

1

The reddish brown colour (1)of the bromine is decolourisbd in sunlight (1) -

2

The purple colour (1) of immediately decolourised

2

the permanganate sol_ution is / pale pink(1)

Eotal 15 uarks

*

T'K

5

6

4

 

-6-

|22L2O2O/CA.PGArSl2O15

CHEMISTRY

UN]T2-PAPER02 Question

i{ARK

SCHEME

2

Specific objectives: l{odule: 2 - L-L, 2-2, 2-3, 2.A, 2'5 (a) (i)

C

T'K

Accuracy

burette at eye levef of filter funnel after adding titrant to burette Reading burette to 2 decimal places (1) Eliminate any bubbles in bureEte tap

Reading

Removal-

not blow out remaining liquid at the tip of the pipette Overshooting the burette Do

AnY

ONE

1

(ii) Precision: Adding titrant drop by drop near the end point Taking successive readings untj-l constant voh:rnes are

(b)

obtainedsuccessive readings until the volume does not dj-ffer Taking (1) by more than 0.1cm3 Faulty calibration of instrument If the student answ€trs in the positive or negatine, acceptArly oNE o High level of purity (1) . Atmospheric stability (1) (1) . Large mofar mass

. Reasonable solubility in titration . Absence of hydrate water (1) o Cheap and readily avai-lable

(c)

(i)

(1)

Any lIEo (2)

Graph: (Page 7) Draw a curve, (1) 6 accurate points fit Best Accepted fit - 1 mark onIY End

(iii)

point volume: 24-5 + 0-5

25 cm3 NaoH

contain

2

4

(1) (2')

(ii)

1

(1)

1

2'o x 25 1000

: 0.05 moles (1) Give the mark for expression NOT the answer. Moles NaoH: HC[: 1:1 Moles HCL : 0.05 24-5 cm3 HCt contaln 0-05 mol-es (1) 2

1000

*

cm3

conEal-n 0-05x1000 24 -5 :2.04 M HCI

Not Earkirrg for unit

(1)

xs

 

-1-

o

22L2O2O I CAPE /Ms / 2 O 1 s

CHEMISTRY

UNIT2-PAPER02 MARK SCHEME

Question 2 cont'd KC

25

(d)

cm3 NaoH added

T'K

to a polystvrene cup using a

pipette. (1) (Sofrrtiot allowed for few minutes)and (1) noted-standing temDerature acid added from burette, mixture ffi stirred and temperature noted. (1) This is:repeated"until a total of 45 sr3 of acid until the (1) temperature stablised' "." "aa"a'or

Total 15 marks

*

xs

4

e

7

4

 

;t.14

a i.il

'

-8-

|22L2A2A / CAPE /t{S /2

01

CHEMISTRY

UNIT2-PAPER02 MARK SCHEME

r..)'iesEion

2 cont'd

.l:;.. LLtrp. r

.*r. l.;. '-F|-

+* -l..-

-i_-

It t

a ,.

& E

u

-l -f

-i-;

j-

I

'-1-r

32

.,-:], r.J."

-r. l-l LI, .-LL -l- t ---

-

' ll

 ,rt -r{+

i Tl : i].1 i; Ii ri.I. i/{

ti l.:

.1,.1 - :

I

-l+--i-

-;*{-F--i -ilt-ird

rl-.- J -f-1--tst-;_ -rln'I -' l'l^:.f

"-

-1'1r'

I

(f) tor 2 ilfutbat llnor (l) tor p.tot tG aooutet tolut.) (2, b..t llt Lbcr

-+,

ri ..r

.l

ffi I il ;- i i

-T .l

ll i ,...-i

--- -

il

I L.

,1

l

+

f

. i'f

-F i-'

i.

 -

li

ii+f;

I

10

*

ls

30

0

33

volur of rcld rddod (crt)

tlfi

5

.

'.'5i l:ii

''Lrt

,:,

+,#,

1 ii;,l ttt:

'i

 

-9-

o22L2O2O lCAPE/Ms /201 s

CHEMISTRY

UNIT2-PAPER02 MARK SCHEME

Question

3

Specifie Objectives:

tfioduJ.e:

3 - L.2,7. ,

1.2, 1.3 KC

(X Increased Decreased pressure/conc. temperaFure (1ofKC,reactants

(a)

usd of d catityst'

(b) (i)

(ii)

:

(1 KcI

KC)

xs

UK

3

i

chatelier's Pr Prin inci cip ple le:: if one or more factors that affect an equilibrium are chanqed, the position of equiltbriurn shift-3 in the direction which opposes the change- (1 XC)

rLe:

. Low terperature (1

o ltigh pressure

(1

1

UK)

2

tII()

(iii)

o The sulfur trioxide is dissolved inLo conc. sulfuric acid to form oleum (1 xS) . The oleum j.s diluted with water to form conc. sulphuric acid .(1 Iq) (iv) o HzSOr(/) + Sog(S) -+H2S2or (1)) o

HzSzoz(|,)

+ Hzoot --+

Z

2 2

2Hzsoa(|,)

For each :eglll: B;+anced (1) + state .s1mbo1s (1) If in b(iii) 'studditts"uied sulphuric acid o..r Qi fute sulphuric acid, state slnnbol for sulphurj-c acj-d must'be ( aq) in part (iv)

(v) Safetyconsiderations Reaction between SO: and vlater is highly exotherrnic (1)

Clouds of sulfuric acid are produced. (1)

and Lo cause can burns acid the skin flesh. sulfuric acid can cause blindness if it gets into the (1) Sulfuric

3

eyes. (1) Use of protective gear

Any

THREE

of. ttre aborTe, 3 x

1 i I

Eotal 15

:\.

G

marks

4

6

5

 

.

. .l :

.r;,1:

.:l-:'.i ' I ':ri'ri

..':r*41 r;r'l; r:

I

':;,'ilt

:.,.:;,:il |'.';) ..: .;:t:ti.

',i:ii.i

'+;,

10-

022L2O2O lCAPE /MS/2

O 1

s

CHEMISTRY

UNIT2_PAPER02 MARK SCI{EME

Question

4

Specific objeetives: Modulei L - 4-L, 4.2, 1.?, 4.4, 4.4, 4-5,.4-5 Addition polymerisdtiurr involves the linkinq of cne type of monomer with double (1) or triple bonds' to roduct ( 1): s ive Lhe pollmer as the

(a)

Condensation polymerj-sation invofves the linking of two types of monomers oR monomeri wi th biilunctiona:. (1) to give, thg two funct onal r polymer and a small molecule such as water or hyd,rogen chloride. (1)

xc I'K

4

Students must mention the tYPe of bon4- and the

amount 4rks to get ttre of products for EACH tYPe of lrclymerization

Carbohydrates/Polysaccharides (1)

(b)

(1) Proteins Note: PoJ-yamides cannot be accepted here siace ttrey include symttretic substances- Polysaccharides are aII naturally occurring. €.9-. glycogen - cellulose (1) starch

3

pecEin albumin

keratin

collagen

(c) EO

AITY oNE

CE2CH2- Of, +

(1)

o

ll

il

c --@- c

EO

ethane':lr 2-dtol

o

OE

beazeDe-I, 4dicarboxylic acid $

o-cEzcB2-o-

o il

c

-@-

+ ouzo

(11 4

o il

c

(1)

(1)

Studeuts will be penal.ized for NOI insertiag ttre 'rf in ttre lrcIyner onIY. &

xsi

.

ri'

 

- 11o

CHEMISTRY

22L2O2O / CAPE /MS/

20 1

s

UNIT2_PAPER02 MARK SCHEME

Question ,l cont'd KC

(d)

The .,Jrink between

because one end

the other end

ilr

the two monomers is of unit is

N

'c:

f,

is

I

-c-llOE

xs

(1)oR

and

ll

o

E

lt'

The remaining part of repeating

unit has

UK

(1).

CE.

-E-C-C-

1

ril

EO

E

and (U

r - cEr- c I

giving

monomers:

I

o

cE-

I'

B--;tr-C-C-OE

,lll EO

(1)'

E

E-tr-cE--c-oE I

'll

4

o

(1)

If 'the breaking of C to N bond i.s shot^rn and the monomers are cortect then the mark awarded is 3 marks- If the breaking of'the-bbnd is not shown then the mark is two. lfotal 15 aarks

7

I

OR

If the parts of the polymer are given (the pollmer has been split and the both halves shown) ,then 1 mk each. The actual monomers shown for each part of the polymer given wi'll r'eceive Lmk each- 4l'trCs

 

:: ::. :.': .il

i .tiii ,,.iai:

,.:.1"

-12-

o22L2O 20 / CaPB /Ms /

CHEM]STRY

20 1

s

UNIT2-PAPER02 MARK SCHEME

Questign

5

ipecific

Objectives: Modulei 2 - 8.7.t 8-2, 8.3,

8

-4, 8.5,

8-6 C

(a)

Chromatography involves the separation of components of a ruixture bet ween two Dhases. (1)

ts of the partitioninq phase. phase (1) mobile and a stationarv Involves

between

I

T'K

a

artitioning occurs because the gomponents of the mixture wiII exp.erience different absorption forces different soi-ubil-itY wi th the mobile phase. (1) If student stetes o iuPLies ttrat a uobiJ.e phase aDd a axists stationary phase - 1Ek (b) (i) The componen ts can be detected by a reagent calfed a loca tinq agent or visualiz inq aqent (1) . This will react with the component and , ryg}gg5

4

Have

compound. (1)

(j-i )

Rr

moved bY solute Distance moved by solvent

= Distance

(1)

1

If eguation is iupJ.ied give the uark

R. of

'

2.5 13.5

= 0.2

1

(1)

t2.5 l-3.5 R-ofR=-=0-9 '

(iii)

Rhasa than Q

eate

t-

(1)

ubilit

l_n

mobile

(1)

yto orb onto t hasas more (1) is oR Q Polar so the stationarv Phase. 1t is stronglY adsorbed onto the stationarY Phase than R which is less Polarof If student says Rr factor of Q and R differ because -of difference in solubilities and differ in ithe levels adsorption onto the stationary phase -€ {EY lEIs

(c)

2

Thin layer chromatograPhY: Separates smafl amounts of compounds (1)

*

2

to separate (dyes, aniao acids, plant pignnents) usla useful if quantificatlon of large amount Less required. (1) Cannot separate compounds of slmilar Rr values' (1) Sauqlles can be removed fr,lrtL ariilysis' (1) Use (1) + conrnent on usefuJ-ness (1)

(1)

are

2

xs

 

,1, . i .'

:ra''

- 13-

..::i:',.:

.':.: l:,;i.,, .::. .t;;:yi:i

o

;a:. -; -:r'

CHEMISTRY

22L2O2O / CAPE /Ms /2

o1

s

UNIT2-PAPER02

r;,,=#'

r

MARK SCHEME

ffi

Question 5 cont'd

Specifie Objectirres: t{odul.ez 2

(c)

-

8.1, 8-2, 8.3, 8-4, 8.5, 9.6 KC

t,K

Column Chromatography:

Large anounts of material- can be separated and collected(1)

Large columns can be'u'sed'for purificationCan be used to prepare compounds. (1) Fractions can be collected for'.analysis- 11)

2

(1)

Use (1) + comeat on;usefuJ.liess (1)

ltota1 15 narks

&

7

I

xs

 

.':

. .

.'

:.

:. ,:

.' .'

.. .

r

'.-il

,:

::

i::':;:.-

::i.,rj

.-.?'] :)ri' .'(+

1,.i1

1 4-

,..'

g22L2O2O ICAPElMS/2O15

CHEMISTRY

UNIT2_PAPER02 i.,IARK SCHEME

Question

6

Specific Objectives: Module: 3 - 6-L, 6-4, 9-2, 3.3 tRc''

CblorLae

(a)

T'K

E1drogea

4'

A

I t

I

I

concentrated sodiurn cbloride solution

3tee1 cathode

fitaniuanode

Sodiun

Diapbragu

solutioD

cotltaEiEated

Must be conc sdiu[ chloride or brine Clz (S) 2 C/-(aq) - 2eAnode i Hz (S) (aq)+ 2e4 Cathode: 2H*

witb

f,aCI

(1 Kc) (1 Kc)

(1 Kc) pglY (2 Kc) labe1s Diagran + 2 (3 Kc) Diagran + 4 J.abels Diagram + 5 or Dore labe1s (4 Kc) Diagrarn

to) Health concern-Iink concern wirh its effect Use of asbestos diaphrasm (LKC) Asbestos deteriorates with use overtime' (t'E) Dry asbestos fibres can be inhaled/ingested causing respiratorY Problems - (Ix) Asbestos is considered to be carcinogenic (UK) Possible leakage of chlorine gas into the environment- (LK) 1 KC + anY 2 IIKs

(,

6

1

2

xs

j

 

,:

"'::

,'

-15-

o

CHEMISTRY

22L2O 20 | CaPE /l,rs /2

01

5

T]NIT2-PAPER02 MARK SCHEME

Question 5 cont'd KC

(c) (i)

Production of

CFCs

I'K

has decl-ined:

cFCs accelerates the It was discovered in the Lg70,s that atmosphere' (1 ulc) the in layer ozone the of depletion Destruction of the ozone Iayer allows harmful w radiation UX) to reach the surface of the EarLh.

(1

3

CFC's are broken down in stratosphere to g ive chlori-ne free radicals which react with ozone to cause its conversion to oxfi-n-(l tK)

(ii)

Products of combustion of fossil fuels COz

is a "greenhouse

gas"

-

Coz:

(1)

Increased concentration of Coz- contributes to the greenhouse (1) effect i'e' qIobal warming' of Negative effect on the atmosphere through melting (x) gficiers and ice-caps increase in sea leve1s' Decreases SOzTCOTNOz

3

productivity of the land emissions ].ead to acid rain

lltr€lmnEEofttreaborreorsirni].ar-3x1nark Tota]. 15 uarks

*

7

I