FOR TEACHERS’ USE ONLY
Se c t i o n A
1.
(a )
M a rk s 1
T : Ch lo r i n e / Cl X : F lu o r i n e / F Z : M a g n e s iu m / M g
(b )
1 Cl
F
(n o m a rk fo r a n y m is ta k e ) (c )
X ( F ) a n d Z ( M g ) f o r m s a c o m p o u n d o f M g F 2( s ) ( Z X
2(
s))
M g F 2 i s a n i o n i c c o m p o u n d w h i c h c a n n o t c o n d u c t e le c t r i c i t y i n s o li d s t a t e . M g F 2 i o n i z e d t o g i v e m o b i le i o n s i n a n a q u e o u s s o lu t i o n , s o a q u e o u s s t a t e c o m p o u n d c a n c o n d u c t e le c t r i c i t y .
1 1
(4 )
2008-C E -C H E M
I -1
FOR TEACHERS’ USE ONLY
2 .
FOR TEACHERS’ USE ONLY
(a )
Is o t o p e s a r e t h e a t o m s o f t h e s a m e e l e m e n t w i t h t h e s a m e n u m b e r o f p r o t o n s b u t
(b )
L e t a %
b e th e %
T h e %
a b u n d a n c e o f
(c )
d iffe re n t n u m b e r o f n e u tro n s
a b u n d a n c e o f
11
B a n d ( 10 0 -a ) %
b e th e a b u n d a n c e o f
11a + 10(100 − a ) = 10.8 100
11
Bis 8 0 % .
10
B.
a = 8 0
It a l s o g i v e s w h i t e f u m e s b e c a u s e 11B i s t h e i s o t o p e s o f s a m e c h e m i c a l p r o p e r t i e s a s 10 BC l 3. 10 BC l 3 + 3 H 2O H 3BO 3 + 3 H C l
M a rk s 1
1
1 10
B, s o
11
BC l 3 h a s t h e
1
(4 )
2008-C E -C H E M
I -2
FOR TEACHERS’ USE ONLY
3 .
C a se
FOR TEACHERS’ USE ONLY
O b s e rv a tio n
E x p la n a tio n
M a rk s
Ir o n -m a d e w ith z in c
o b je c t
fu lly
p la te d
No c h a n g e
Z n p l a t e d o n t h e i r o n . It c a n p r e v e n t w a t e r a n d o x y g e n in a ir fro m c o n ta c tin g w ith i r o n . No r u s t i n g o c c u r s .
1
Ir o n -m a d e w ith tin
o b je c t
fu lly
p la te d
No c h a n g e
S n p l a t e d o n t h e i r o n . It c a n p r e v e n t w a t e r a n d o x y g e n in a ir fro m c o n ta c tin g w ith i r o n . No r u s t i n g o c c u r s .
1
Ir o n -p l a t e d o b j e c t f u l l y p l a t e d w ith z in c , b u t p a rt o f th e z in c s c ra tc h e d to e x p o s e th e iro n u n d e rn e a th
Z n d is s o lv e d
Z n s a c rific ia lly p ro te c ts F e e x p o s e d fro m ru s tin g .Z n d o n a te s e le c tro n s to F e , s o Z n is o x id iz e d .
1
Ir o n -p l a t e d o b j e c t f u l l y p l a t e d w ith tin , b u t p a rt o f th e z in c s c ra tc h e d to e x p o s e th e iro n u n d e rn e a th
B lu e c o lo u r o b s e rv e d n e a r th e s c ra tc h in g .
F e is m o re re a c tiv e th a n S n , s o F e s a c rific ia lly p ro te c ts S n fro m o x id a tio n .F e d o n a te s e le c tro n s to S n , s o F e is ru s te d .
1+ 1
(5 )
2008-C E -C H E M
I-3
FOR TEACHERS’ USE ONLY
4 .
FOR TEACHERS’ USE ONLY
(a )
O b s e r v a t i o n : M g d i s s o l v e d . So m e c o l o u r l e s s g a s b u b b l e s a p p e a r e d M g ( s ) + H C l ( a q ) M g C l 2( a q ) + H 2( g )
(b )
Th e r e a c t i o n i n s i d e t h e t e s t t u b e i s e x o t h e r m i c . Th i s i n c r e a s e s t h e t e m p e r a t u r e o f t h e c a r b o n a t e d w a t e r . Th e n t h e d e c o m p o s i t i o n o f c a r b o n i c a c i d i n c a r b o n a t e d w a t e r is s p e e d e d u p .
M a rk s 1 1
1 1
(4 )
2008-C E -C H E M
I -4
FOR TEACHERS’ USE ONLY
5 .
(a )
(b )
El e c t r o n f l o w : f r o m
FOR TEACHERS’ USE ONLY
M g to Z n
M g i s m o r e r e a c t i v e t h a n Z n / M g h a s a h i g h e r p o s i t i o n i n E. C . S . , s o M g te n d s to lo s e e le c tro n s to Z n e le c tro d e . (i) (ii)
M a g n e s iu m / M g . M g u n d e rg o e s o x id a tio n . M g ( s ) M g 2+( a q ) + 2 e
M a rk s 1
1 -
1
(c )
Th e s t r i p s p e n e t r a t e d i n p o t a t o B .
1
(d )
It c o n t a i n s e l e c t r o l y t e f o r c o n d u c t e l e c t r i c i t y .
1
(e )
Th e r e a d i n g o f m u l t i m e t e r b e c o m e s z e r o .
1 (6 )
2008-C E -C H E M
I -5
FOR TEACHERS’ USE ONLY
FOR TEACHERS’ USE ONLY
6 .
(a )
St a t e Mi s t a k e 1
Mi s t a k e 2
th e
m is ta k e
e x p la in
Su g g e s t a m e t h o d f o r c o r r e c t i o n
Up w a r d d e l i v e r y ( d o w n w a r d d is p la c e m e n t) fo r c h lo rin e g a s
Us e d o w n w a r d d e l i v e r y o f g a s t o c o l l e c t C l 2( g ) .
1+ 1
Us e
1+ 1
w h y it is w ro n g
a n d
is u s e d . C h lo rin e g a s is d e n s e th a n a ir.
( Tw i s t t h e r e c e i v e r a n d t h e g a s j a r u p s i d e d o w n .)
m o is tu C a O w C a O (s C
re m o v e m o is tu re .
C a O
is
u se d
to
re m o v e
re . o u l d r e a c t w i t h C l 2. ) + C l 2( g ) a C l 2( a q ) + C a ( O C l ) 2( a q )
a n h y d ro u s
Mg C l 2( s )
(b )
C a r r y o u t th e e x p e r im e n t in f u m e c u p b o a r d s in c e C l2p r o d u c e d is h ig h ly to x ic .
(c )
(i) (ii)
O C l -( a q ) + 2 H
+
( a q ) + C l -( a q ) C l 2( g ) + H
2O
to
(l)
O C l is th e o x id iz in g a g e n t. Wh e n O C l - i s c h a n g e d t o C l 2, t h e o x i d a t i o n n u m b e r i s c h a n g e d f r o m -
Ma r k s
Th e o x i d a t i o n n u m b e r C l d e c r e a s e s .
+ 1to 0 .
1 1 1 1
(8 )
2008-C E -C H E M
I -6
FOR TEACHERS’ USE ONLY
7 .
(a ) (b )
M a rk s 1
A : F ra c tio n a l d is tilla tio n
B : Cr a c k i n g (i)
(ii)
(c )
FOR TEACHERS’ USE ONLY
(i)
(ii)
Di e s e l Di e s e l d ie s e l P e tro l
1
h a s a h ig h e r v is c o s ity . h a s h i g h e r m a s s a n d l a r g e r s i z e , s o t h e v a n d e r W a a l ’s fo r c e b e t w e e n m o le c u le s is la rg e r. is c le a n e r.
1
Th i s p r o c e s s c a n c o n v e r t t h e h e a v y fr a c t i o n s ( w i t h l o w e r d e m a n d ) t o l i g h t e r fr a c t i o n s ( w i t h h i g h e r d e m a n d ) . Th i s r e d u c e s t h e w a s t a g e o f h e a v y fr a c t i o n s a n d h e l p s t o m a k e m o r e p r o fi t .
1
P e tro l h a s lo w e r n u m b e r o f c a rb o n in th e m o le c u le s , s o it c a n b u rn m o re c o m p le te ly .
(I)
D i s C4H8.
H3C
CH2
CH
CH2
but-1-ene
(II)
or
H3C
CH
CH
but-2 -ene
A d d B r 2in h e x a n e to th e tw o s u b s ta n c e s in d a r k n e s s . C20 H42 h a s n o c h a n g e . D ( C4H8) d e c o l o u r i z e s t h e o r a n g e b r o m i n e .
CH3
1
1 1
1 1 Br Br
H 3C
CH2
CH
CH2
+
Br2
H3C CH2
C
CH
(9 )
2008-C E -C H E M
I -7
FOR TEACHERS’ USE ONLY
8 .
(a )
M a rk s 1
Ad d i t i o n p o l y m e r i z a t i o n .
(b )
H
H
CN
C
n
C
C
H
C O
(c )
FOR TEACHERS’ USE ONLY
H
H
OCH3
1
CN C C O
OCH3 n
CN
C
1+ 1
C
H
C CH3 HO CH3
O (d )
Ad d s o m e d r y i n g a g e n t t o p r e v e n t w a t e r f r o m a c tiv e in g re d ie n t.
in itia l th e a d d itio n p o ly m e riz a tio n o f
1
(5 )
2008-C E -C H E M
I -8
FOR TEACHERS’ USE ONLY
9.
FOR TEACHERS’ USE ONLY
C h e m ic a l k n o w le d g e (6 m a rk s ) A . Pr e p a r a t i o n o f e t h a n o i c a c i d f r o m e t h a n o l 1. Ox i d a t i o n o f e t h a n o l b y K 2C r 2O7 w i t h a c i d i f y i n g w i t h c o n c . H2S O4.
Ma x . 2
B .
Ma x . 4
2.
is o la te p u re e th a n o ic a c id fro m
p ro d u c t b y fra c tio n a l d is tilla tio n .
E s te rific a tio n o f e th a n o ic a c id a n d e th a n o l 1. R e a c t i o n b e t w e e n e t h a n o i c a c i d a n d e t h a n o l w i t h t h e u s e o f c o n c . H2S O4 a s c a ta ly s t He a t i n g u n d e r r e f l u x t o p r e v e n t l o s s o f v o l a t i l e s u b s t a n c e s A d d th e p ro d u c t m ix tu re to w a te r to re m o v e u n re a c te d p ro d u c ts . Ob t a i n t h e u p p e r l a y e r b y d e c a n t a t i o n
2. 3. 4 .
5 .
(6 )
E ff e c tiv e c o m m u n ic a tio n ( 3m a r k s )
G e n e ra l g u id e lin e s fo r m a rk in g e ffe c tiv e c o m m u n ic a tio n : (i) T h e m a rk fo r e ffe c tiv e c o m m u n ic a tio n s h o u ld re la te to th e c a n d id a te ’s k n o w le d g e in c h e m is try .A c a n d id a te w h o w ro te a p a ra g ra p h w h ic h is to ta lly u n re la te d to th e
(ii)
q u c o T h k n
e s tio m m u e ta o w le
n sh n ic a b le d g e
o u tio b e a n
ld d e s e rv e z e ro m a rk s b o th in c h e m ic a l k n o w le d g e a n d in e ffe c tiv e n . lo w illu s tra te s th e re la tio n s h ip b e tw e e n th e m a rk fo r c h e m ic a l d th e m a x im u m m a rk fo r e ffe c tiv e c o m m u n ic a tio n , to g e th e r w ith th e
p o in ts to b e c o n s id e re d in m a rk in g e ffe c tiv e c o m m u n ic a tio n . Ma r k f o r c h e m i c a l
m a rk fo r
k n o w le d g e
e ffe c tiv e c o m m u n ic a tio n
3o r a b o v e
2
4 o r a b o v e
(iii)
Ma x i m u m
3
Po i n t s t o b e c o n s i d e r e d i n p a ra g ra p h (iii) b e lo w (A ), (B ) a n d (C ) (B ) a n d (C )
T h e th re e m a rk s fo r e ffe c tiv e c o m m u n ic a tio n a re a w a rd e d a s fo llo w s : (A ) th e a b ility to p re s e n t id e a s in a p re c is e m a n n e r, in c lu d in g th e p ro p e r u s e o f c h e m ic a l te rm s (th is m a rk s h o u ld n o t b e a w a rd e d to a n s w e rs w h ic h c o n ta in e d
1
(B )
a lo t o f in c o rre c t/s u p e rflu o u s m a te ria ls ); t h e a b i l i t y t o p r e s e n t i d e a s i n a s y s t e m a t i c m a n n e r ( i .e ., t h e a n s w e r i s e a s y t o
1
(C )
a n d to e x p re s s id e a s u s in g fu ll
1
2008-C E -C H E M
fo llo w ); th e a b ility to p re s e n t a n s w e r in p a ra g ra p h fo rm s e n te n c e s .
I -9
FOR TEACHERS’ USE ONLY
( 3)
FOR TEACHERS’ USE ONLY
Section B 10 . ( a )
(i)
(ii)
V a n a d iu m
(V ) o x id e / V
2 O5
/ P la tin u m
/ P t
SO3( g ) i s a b s o r b e d b y c o n c . H2SO4( l ) t o f o r m SO3( g ) + H2SO4( l ) H2S2O7( l )
M a rk s 1
o le u m
1
Th e o l e u m i s t h e n a d d e d t o w a t e r t o g i v e c o n c . H2SO4( l ) H2S2O7( l ) + 2H2O( l ) 2H2SO4( l )
(b )
1
(i)
2
(ii)
(iii)
Un d e r 4 o f SO3 te m p e ra ra te o f r No . o f m
0 0 oC , t h e f u r t h e r d e c r e a s e i n t e m p e r a t u r e o n l y i n c r e a s e t h e p e r c e n t a g e c o n v e r t e d v e r y s l i g h t l y . Th e r e f o r e , w e n e e d t o h i g h l y d e c r e a s e t h e t u r e t o g e t 10 0 % c o n v e r s i o n . Ho w e v e r , t h i s i s i m p r a c t i c a l b e c a u s e t h e e a c tio n is to o s lo w . o l e o f S = ( 3 2.1 x 10 0 0 ) / 3 2.1 = 10 0 0 0 m o l S( s ) + O2( g ) SO2( g )
1
1
No . o f m o l e o f SO2 = No . o f m o l e o f S = 10 0 0 0 m o l
Fr o m t h e g r a p h , a t 4 5 0 oC, 96 .5 % o f SO2 c a n b e c o n v e r t e d , No . o f m o l e o f SO2 c o n v e r t e d = 10 0 0 0 x 0 .96 5 = 96 5 0 m o l
1
No . o f m o l e o f SO3 = 96 5 0 m o l V o l u m e o f SO3 f o r m e d = 98 0 0 x 5 8 .2 = 5 6 16 3 0 d m
1
2SO2( g ) + O2( g ) 2SO2( g )
3
(a c c e p t v a lu e b e tw e e n 5 5 8 7 0 0 a n d 5 6 4 6 0 0 )
2008-C E -C H E M
I -1 0
FOR TEACHERS’ USE ONLY
(6 )
11. ( a )
(i) (ii)
( 1)
FOR TEACHERS’ USE ONLY Ma r k s 1
C u O( s ) + H2SO4( a q ) C u SO4( a q ) + H2O( l )
( 2 ) To e n s u r e a l l H2SO4( a q ) h a s b e e n r e a c t e d . By f i l t r a t i o n
1 1
Ob t a i n C u SO4 s o l u t i o n b y f i l t r a t i o n
C u O + C u SO4 s o l u t i o n C u O( r e s id u e ) C u SO4 ( f i l t r a t e ) (iii)
(iv )
W a t e r i s s l o w l y e v a p o r a t e d f r o m t h e s a t u r a t e d s o l u t i o n . Th e n t h e a m o u n t o f w a t e r i s r e d u c e d . So m e C u SO4 i s l o n g e r s o l u b l e i n t h e s o l u t i o n . It c o m e s o u t a n d b e c o m e s s o l i d c r y s t a l . Al l o t h e r C u SO4 s l o w l y c o m e s t o g e t h e r t o f o r m la rg e r c ry s ta l. ( 1) He a t i n g c a n d e h y d r a t e t h e h y d r a t e d c r y s t a l . C u SO45 H2O( s ) C u SO4( s ) + 5 H2O( s ) (2 )
(b )
(i) (ii) (iii)
2008-C E -C H E M
P u t th e c ry s ta l in d e s ic c a to rs fo r s e v e ra l d a y s .
No . o f m o l e o f H2SO4 = 1 x 0 . 15 = 0 . 15 m o l No . No . No t It i s d is s
I -1 1
o f m o le o f m o le a ll th e C b e c a u se o lv e d in
o f C u SO4 f o r m e d i n s t e p o f C u SO4 c r y s t a l f o r m e d u SO4 i s c o n v e r t e d t o c r y , a fte r th e c ry s ta l h a s b e e t h e s o l u t i o n . Th i s s o l u t i o
1 = No . o f m f i n a l l y = 16 s ta ls . n g ro w n , so m n is d is c a rd e
1
a
1 1
(6 )
o l e o f H2SO4 = 0 . 15 m o l .2 / 2 4 9 .6 = 0 .0 6 4 9
1 1
e o f t h e C u SO4 s t i l l d b y filtra tio n .
1
FOR TEACHERS’ USE ONLY
(3 )
12 . ( a )
FOR TEACHERS’ USE ONLY M a rk s
S tru c tu re : G ia n t m e ta llic s tru c tu re
E a c h t u n g s t e n a t o m l o s e s i t s o u t e r m o s t e l e c t r o n s t o f o r m t h e s e a o f e l e c t r o n . Th e n t h e t u n g s t e n c a t i o n s f o r m e d . Th e a t t r a c t i o n b e t w e e n t h e c a t i o n s a n d t h e s e a o f e le c tro n s h o ld th e s tru c tu re to g e th e r. e
2+
e e
2+
e e 2+
e e
2+
e e 2+
e e 2+
e e
2+
e e 2+
e e 2+
e e
2+
1 1
e
e 2+
e
Th i s a t t r a c t i o n i s c a l l e d m e t a l l i c b o n d .
1 (3 )
(b )
(c )
Fi l a m e n t w ith o u t m Th i s p r o te m p e ra tu
s h o u ld h a v e v e ry h ig h m e ltin g p o in t / c a n w ith s ta n d h ig h te m p e ra tu re e ltin g . p e rty p re v e n ts th e fila m e n t fro m m e ltin g a n d b re a k in g a t h ig h e r re .
W h e n th e fila m e n t is e m ittin g lig h t, it is h e a te d a t a v e ry h ig h te m p e ra tu re . A t t h e h i g h t e m p e r a t u r e , t u n g s t e n w o u l d r e a c t w i t h o x y g e n i n a i r . Th e n , t h e
fila m e n t is b ro k e n .
(d )
(e )
No t a l l o f t h e e n e r g y i s c o n v e r t e d t o l i g h t , p a r t o f i t i s c o n v e r t e d t o h e a t .
2008-C E -C H E M
I -1 2
1 (2 )
1 ( 1)
A rg o n g a s / A r A r g o n g a s i s a n i n e r t g a s . It w o u l d n o t r e a c t w i t h t u n g s t e n e v e n i n h i g h te m p e ra tu re .
1
FOR TEACHERS’ USE ONLY
1 1 (2 ) 1
( 1)
FOR TEACHERS’ USE ONLY
13. C h e m i c a l k n o w l e d g e ( 6 m a r k s ) Fo r e a c h m e t h o d , 1 m a r k i s r e w a r d e d f o r t h e r e a g e n t , 1 m a r k i s r e w a r d e d f o r t h e p o s itiv e r e s u lt.E a c h m e th o d c a n r e w a r d f o r m a x im u m 2m a r k s . A .
B .
C .
Me t h o d 1 1. B y a d d i n g B a ( N O 3)2( a q ) 2. B a 2+( a q ) f o r m s w h i t e p r e c i p i t a t e w i t h H2S O 4( a q ) B a 2+( a q ) + H2S O 4( a q ) B a S O 4( s ) + 2H+( a q )
Ma x . 2
Me t h o d 3 1. B y a d d i n g Mg m e t a l 2. H2S O 4 r e l e a s e d c o l o u r l e s s g a s w h i c h w o u l d g i v e a “p o p ” s o u n d b y b u r n i n g
Ma x . 2
Me t h o 1. B 2. B b
d 2 y a d d in g a p ie c e o f C u m e ta l r o w n g a s w o u l d b e r e l e a s e d f o r m HN O 3( a q ). It i s b e c a u s e C u i s o x i d i z e d y HN O 3 t o g i v e N O w h i c h i s t h e n f u r t h e r o x i d i z e d t o g i v e b r o w n N O 2( g )
s p l i n t . It i s b e c a u s e H2S O
4
r e a c t s w i t h Mg t o g i v e H2 g a s .
E ff e c tiv e c o m m u n ic a tio n ( 3m a r k s ) G e n e ra l (i) T h in q u
(ii)
c o T h k n p o
g u id e lin e s fo r e m a rk fo r e f c h e m is try .A e s tio n s h o u ld
m m u n e ta b o w le d in ts to Ma
m a rk in g e f fe c tiv e c o m c a n d id a te w d e se rv e z e
ic a tio n . le b e lo w g e a n d th e b e c o n s id e rk fo r c h e m k n o w le d g e 4 o r a b o v e 3o r a b o v e
illu m a re d ic a
fe c tiv e m u n ic h o w r ro m a r
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u n ic a tio n : s h o u ld re la te to th e c a n d id a te ’s k n o w le d g e p a ra g ra p h w h ic h is to ta lly u n re la te d to th e th in c h e m ic a l k n o w le d g e a n d in e ffe c tiv e
s tra te s th e re la tio n s h ip b e tw e e n th e m x im u m m a rk fo r e ffe c tiv e c o m m u n ic a tio n in m a rk in g e ffe c tiv e c o m m u n ic a tio n . l Ma x i m u m m a r k f o r Po i n t s e ffe c tiv e c o m m u n ic a tio n p a ra 3 (A 2
a rk fo r c h e m ic a l , to g e th e r w ith th e to b e c o n s id e re d in g r a p h ( iii)b e lo w ), ( B ) a n d ( C ) (B )a n d (C )
(iii) T h e th re e m a rk s fo r e ffe c tiv e c o m m u n ic a tio n a re a w a rd e d a s fo llo w s : (A ) th e a b ility to p re s e n t id e a s in a p re c is e m a n n e r, in c lu d in g th e p ro p e r u s e o f c h e m a lo t (B ) th e a fo llo (C ) th e a
ic a l te rm s (th is m a rk s h o u o f in c o rre c t/s u p e rflu o u s m b ility to p re s e n t id e a s in a w ); b ility to p re s e n t a n s w e r in
s e n te n c e s .
2008-C E -C H E M
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ld n o t b e a w a rd e d to a n s w e rs w h ic h c o n ta in e d a t e r i a l s ); s y s t e m a t i c m a n n e r ( i .e ., t h e a n s w e r i s e a s y t o p a ra g ra p h fo rm
a n d to e x p re s s id e a s u s in g fu ll
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1 1 ( 3)
FOR TEACHERS’ USE ONLY