C
L
3
6
Cambridge Chemistry Challenge Lower 6th
June 2015
Marking scheme for teachers
(please also read the additional instructions)
p4
p5
p6
p7
Total
16 12 13
6
10
3
60
p2
mark
p3
Page 1
1(a)
(i)
from mercury(II) oxide:
2HgO
(ii)
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blank
equations (underline reduced element):
2Hg + O2

2
from silver(I) carbonate:
2Ag2CO3
4Ag + 2CO2 + O2
2

(iii) from potassium nitrate(V):
2KNO3
2KNO2 + O2

2
(iv) from sulfuric acid and manganese(IV) oxide:
2H2SO4 + 2MnO2
2MnSO4 + 2H2O + O2

[ Half quantities accepted. 1 mark for equation; 1 for underlined ]
1(b)
dot & cross diagrams
[could be
swapped ]
×
×× ×
O

××
C × ××
O ×O××
2–
O
××

B × ××
O ×O××
×× ×
× ××
(i) formula = CO3
×
×× ×
×× ×
× ××
3–
(ii) formula = BO3

2

2
2
×
×× ×
O
××
××
×× ××
O
O
××
×× ××
O
neutral compound isoelectronic with nitrate(III) ion:

ozone 
[also allow CF2, difluorocarbene, or O=N–F, nitrosyl fluoride]
formula:
O3
2

(iii) formula = O4
1(c)

name:
2
Page total
16
Page 2
1(d)
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blank
activation energy for puckered-ring O4 from O2:
= 480.0 – 89.3 + 48.7 = 439.4 kJ mol–1
Ea
pinwheel
O2

89.3
48.7
480.0
puckered
ring O2
4
[2 marks if worked out
standard enthalpy of
formation of puckeredring O2 = 390.7 kJ mol–1]
Ea
O2
1(e)
A=
16O +
2
+
C = 16O218O2

B=
18O +
2
1
[1 mark if all three correct]
1(f) tick the shape(s) most consistent with the data:



3
[1 mark each; lose 1 mark for any wrong (down to zero)]
1(g) time taken:
k.e. of O4 molecule = 4.00 keV = 4000 × 1.602 × 10–19 J
k.e. = ½ m v2
∴v=
= 6.408 × 10–16 J
2 × (k.e.)
m
mass of 18O4 = 18.00 × 4 g mol–1 ≡
18.00 × 4
6.022 × 1023 × 103
= 1.1956 × 10–25 kg
v=

kg molecule–1

4
2 × 6.408 × 10–16 = 103 500 m s–1
1.1956 × 10–25

time of flight =
0.100 m
103 500 m s–1
= 9.66 × 10–7 s (≈ 0.1 µs)

[lose 1 mark each time a power of ten is incorrectly used]
Page total
12
Page 3
2(a)
i)
zero
ii)
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blank
3, 5


4
iii)
iv)
4, 6, 9
1, 8


[zero marks for part containing missing / additional wrong answers]
2(b) circle one or more:
Free radical
Nucleophilic
Electrophilic
Substitution
2
Addition


[–1 mark for any wrong down to zero]
2(c)
three alkenes:


3

2(d)
i)
13, 16
ii)

14, 18

4
iii)
iv)
12, 18

16, 17

[zero marks for part containing missing / additional wrong answers]
Page total
13
Page 4
2(e)
leave
blank
for α-terpineol
i) connect:
&
d
j

[only structure of B+ required
no labels on it needed]
ii) Carbocation B+:
f
i
e
d j
A
f
i
e
j
c
a
d
b

B
a
for borneol
i) connect:
c
&
ii) Carbocation
C+:
a

[only structure of C+ required
no labels on it needed]
a
g
c
cyclisation
d
f
g
b
c
e
e
j
f
i
b
g
2

d
j
i
h
B
h
2(g)
cyclisation
c
b
2(f)
2
h
g
h
g
C
for β-pinene
c
i) connect:
&
i

ii) Carbocation D+:
a
c
g
h
a
cyclisation
d
e
f
b
[only structure of D+ required
no labels on it needed]
e
j
i
B
f
g
b
c
d
e
d
j
i
h
D
f
c
2
a
b
j
i
g
h

Page total
6
Page 5
leave
blank
2(h)
Cation U+:
1
O H
H

2(i)
2(j)
connections:
[only connections required
-1 mark for any incorrect a
down to zero]
b
h
c
j
i
g
u
d
s
f
V
k
l
e
t
r
q to k
m
o
q
also allowed
n
instead of
t to k
p
c to g 
l to f 
j
t to k 
u
s
H
H
o
q
c
g
l
n
b
h
i
k
t
r
a
m
d
f
H
3
e
W
p
Compound X
O
H
H
H
[1 mark for enol]
3
H



H
OH
H
Compound Y
H
O
H
3
H
H
O
H
O
Page total
10
Page 6
2(j)
leave
blank
Anion Z–
O
H
O
H
or
H
H
H
O
O
H
H
O
O
H
3



[ either structure fine ]
Page total
3
Page 7