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2.
(a)
Cr-aa
Y'' t
/
(b) (D
The
products
of crackingcontained nsaturated
h:rdrocarbons)
alkenes
C=C'/ ethene/
reasonablb ame
of alkene
carbon-carbon
oublebond
must
be shown f usingmolecular
formulal which decolourisedhe brominewater mmediately
by addition eaction.
C2
's
a
(ii)
The
products
of cracking also contained aturated
hydrocarbons)
alkanes methane/
reasonable
ameor
molecular
ormulaof alkane
do
not
acceptC-C] which decolourised
the
brominewater slowly by substitutioneaction.
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/ t
'/ '
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C
+
\
1i,',"'.f1(---
i" f;:,{
.
(a)
L-rt{rf
OCI'+
Cl'
+
2H*
*
Clz
+
H2O
or
NaOCI
2HCt--+
Cl2
+
HzO
+
NaCl
Chanee
from
colourless)
o
bpw:{y-qllp:Y
Ci,
+
Zl'
ZCI-
Iz
or
Cl2
+
zKl
+
2KCl
+
lz
(ii)
Noobservablechange/reaction
o'/,
h,,4-&
\Gv€
ttfqit ,-(
r rced/ lcsshnrmful to,
'
t l less
(c)
lesi ctreniicils
are
used
less
harmful
o
environmen
money
save
ime
ldo
not
accept
eaction
asterl
.q
dangerous
easY
o
han
dle
save
I
I
1
41
[1\rt1(
4.
(a)
Both
vinegar
and
wine
contain
$ot69ut:sa-
?
unl.1
s
'.{'
(
"'
''k
Only vinJgar (ethanoicacid) ffi in water / contains mobile)
electricitY.
(b)
(D
Ps+fe2+*2e-
( i i )
ztf
+2i
-Hz
(c)
Iron
reacts
irectly
with
vinegar/fl*(aq)
iving out
hydrogen
as.
5, (a )
(b)
(c)
Zn+ 2H*- Znz* Hz or Zn+2HCl- ZnClz Hz
Z
^
t'::
{ i -
t i , . , , , " , f ;Y i .* :s
I
ions
for conducting
1
tl:
avi l
{
l,.t-{L
{
left
behind
I
I
I
(t
t f - i r
1
I
I
1
No further
gas
gvolveo
r*u drc.t.r,( 5"
{.&b
t.''up-"/fit' '
;r,.\.pL
gr.
.
,.f
7
To
wash
away
Zn*
I
Cl' lH*
lZnCl2
/HCl
lacid
Dgaqt
4-c-c-ept
mpurit ies]
d
Copper
will
be
oxidized
/
become
co
oxide
/ copper
reacts
with
o
en
(or
air)
(e)
Percentage
f
zinc
by
mass
n
the
sample
(2.00 1.75)
2,00
100%
=
12.5oA
AF
A**
'f^
tYtatatL
aOO7-CE-CHEM
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i
'J
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MgO+Clz+C-*
MgClr+CO
or 2MgO
+ZClz+C
-ZMEClz+COz
t
redox
reacti
n)
t
displacement
reaction)
Potassium
s a
more
powerful
educing
gent
more
eactive
han
magnesium.
(c) (i) electrolysis
(ii)
Magnesium
chloride
s an
electricity
in
molten
state/
contains
obile ons.
(d)
sacrificial
rotection
making
alloy firework
flash
do
not accept
pplication
f MgO]
r., .yrt ,L
f
concentrated
odium ydroxide olution
'
^
.7,
r-
1:'
{,(''
t'5
5'
L'rrr
}
(white) olid./powder
do.not
ccgptprecipitateJeft ' -
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9.
Chemicallkowledge
6
marks)
Corrosive
rooerly
o
safety
glasses
goggles
rubber
gloves
protective
lothings avoid
contactwith skin
or eyes I
wash
with
plenty
of
water
f contacted
ith
skin
o
because
cidof high
concentration
s cofrosive
'.1
.;',
t:,
'(.,-rr1r-,J
"
DilUtion rg.ce_ss
o
add
slowly)
small amount
of
rust emover
nto a
largeamountof water
with
stirring)
I
r
because
arge amount
of heat
given
out
in dilution of the rust remover
(acid
of
high I
concentration)
avoid
rust remover
acid)
splashing
ut
'
n,
o
..
".1.*,
,.j;;1 i\w.
u<
ttnir
,
'
, ; ' . t - ' '11
1- r
Otherpotential
aneers
\'
'i('{th'r"L{"rv
;-
*.
ptasti.
"ontainer
instead
f metal
do not
use o cleanmarble
do-'notmix with
chlorine
I
bleach
r caustic oda
do not
put
n
warm
place
o
because
ill
damage
metal
container
damage
marble toxic
gas
evolvesf mix
with chlorine
I
blpach large
amount
of heat
eleases
f mix with caustic oda/
acidic
gas
evolves f
put
in
(. -. -, ' r ,
\ r; ' r t '
warm
place
.".. r
i,
"r,._,r_
i
,,
r,n
f
tr,t"";,^
\
t,rr:\
pp.,t
,l*,e+i'
i
\
u. ,
- * l , r *" . -Y\
i
-
( ' ' "5 ' - i : t
c l ' ' * . ( i ' . ' - i1*- "1( ' 'u-
,,j
1]
"
"*-\
t
'''a-"i(
f,k
I-"
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-
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Section
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x
(
tt
r
i'-..
'' '
"t'
t
/
f
c
, , )
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P
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t2.
(a)
Molerat ioofC:H:O
0.401
0.069
0.531
=-r- t-
12
I
16
(step-mark)
FOR
TEACHERS'
:g/
3>
x
dr(
l*
=
0.033
0.068
0.033
-l :Z:
I
Ernpirical
ormula
of
Z:
CH2O
(b)
Let
he
molecular
ormula
of
Zbe
(CH2O)"
formula
mass
of Z
=
-*;-
x24
=60
(step-mark)
(400
1000)
--
\---r
---E'r/'
(12+2+16)n=60
n
(, : ,03)):o.ct66
.
n:2
a\ :_. ,
\1
X.
Molecular
ormula
of
ZisC2HaO2
W#4t
t.
q,,ttt->T
(c)
(i)
HCoOcH3
Explanations:
/
[Ja
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FOR
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13.
Chemical
nowledge
6
marks)
The
ollowing5
points.
mark or
each
oint
.;:''.'"
'
1'-n''
"(
nve ionic
group
headand ong hydrocarbon
hain tail.
ravehydrophilic
property
andhydrophobic
roperty.
ls, while soapless etergents
ade rom
petroleurn.
g:
I
,
while
soapless
etergents
ave
SOr-
/
-OSO3-
group.
ardrvater acidic
medium,while soapless
etergents
an.
i \
L'I
.t
\
/ \ : " ' \ -Lr , - r {
;
^^i"t
I
I
'
,t -
.l\tl,-
U
.
i
,
\
\
(B )
Effective
ommunication
3
marks)
General uidelinesor marking ffective ommunication
\
t-
---'
il
"i
"''
\
-----/'
'J
?,
,
e
Both soapyand
soapless etergents
ct aswctting
agents.
r
Both
soapyand
soapless etergents
ct asemulsi&ing
agents.
o
Soapy
detergents reusually
biodegradable, hile soapless etergents sually
arenot.
o
Soapless
etergents
anbe ailor-made,
while
soapydetergents
annot.
(6)
( i i)
(i)
The
mark for effective
communication hould elate o the
candidate's
nowledge
n
chemistry.
A candidate
who wrote a
paragraph
hich
s
totally unrelated
o the
question
should
eserve eromarks oth
n chemical nowledge
nd
n effective
ommunication.
The table
below illustrates he
relationship etween
he mark
for chemical
knowledge
and the maximum
mark for effectivecommunication,ogetherwith
the
points
o be
considered
n marking ffective
ommunication.
(iiD
The hreemarks
or effective
ommunicationre
awarded s
ollows
(A)
the ability
to
present
deas n
a
precise
manner,
ncluding he
proper
use of
chemical
erms
(this
mark
shouldnot
be awarded
o answers
hich
contained
a lot
of incorrecVsuperfluous
aterials);
(c)
the ability
to
present
deas
n
a systematic
manner
follow);
the ability
to
present
answer in
para9raph
orm and
sentences.
(i.e.,
he
answer s
easy
o
I
to express
deasusing
full
I
-r
/+
( . ,
Y.
r{
K"
P;-
i v ' -
\.
.
"a
/. J
2007-cE-cHEM-10
mark or chemical
knowledge
maximum mark
for effective
communication
points
o
be
considered
n
paragraph
(iii)
below
4 or
above
3
(A),
(B)
and
c)
3 or
below
2
(B)
and
c)
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