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CAMBRIDGE INTERNATIONAL EXAMINATIONS
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Cambridge International Advanced Subsidiary and Advanced Level
MARK SCHEME for the October/November 2014 series
9701 CHEMISTRY
9701/21
Paper 2 (AS Structured Questions), maximum raw mark 60
This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of
the examination. It shows the basis on which Examiners were instructed to award marks. It does not
indicate the details of the discussions that took place at an Examiners’ meeting before marking began,
which would have considered the acceptability of alternative answers.
Mark schemes should be read in conjunction with the question paper and the Principal Examiner
Report for Teachers.
Cambridge will not enter into discussions about these mark schemes.
Cambridge is publishing the mark schemes for the October/November 2014 series for
most Cambridge IGCSE®, Cambridge International A and AS Level components and some
Cambridge O Level components.
® IGCSE is the registered trademark of Cambridge International Examinations.
Page 2
Mark Scheme
Cambridge International AS/A Level – October/November 2014
Syllabus
9701
Paper
21
Question
Mark Scheme
1
increasing distance of (outer) electron(s) from nucleus
OR increasing distance of outer / valence shell from nucleus
1
increased shielding / screening (from inner shells)
1
reduces attraction
1
(3rd electron for each in) inner / lower energy level / shell / closer to nucleus
(than first two) / less shielding
1
(large) increase in nuclear attraction
1
[2]
(1s2 2s2 2p6) 3s2 3p6 3d10 4s2 4p6 5s2
1
[1]
(ii)
four isotopes owtte
1
[1]
(iii)
(84 × 0.56) + (86 × 9.86) + (87 × 7) + (88 × 82.58)
100
= 87.7 (must be 3 sig figs)
1
1
[2]
(a species that) gains / takes electron(s)
1
[1]
(a) (i)
(ii)
(b) (i)
(c) (i)
Marks
© Cambridge International Examinations 2014
Total
[3]
Page 3
Question
(ii)
Mark Scheme
Cambridge International AS/A Level – October/November 2014
Mark Scheme
Syllabus
9701
Paper
21
Marks
Ba
Cl
O
45.1
137
23.4
35.5
31.5
16
0.329
0.329
0.659
0.329
1.969
0.329
1.00
2.00
5.98 / 6
Total
1
1
emp form = BaCl2O6
1
[3]
X = Mg(OH)2
Y = MgO
Z = Mg(NO3)2
1
1
1
[3]
reagent = nitric acid
1
MgO + 2HNO3 → Mg(NO3)2 + H2O
1
[2]
(iii)
Heat / thermal decomposition
1
[1]
(iv)
Mg + 2H2O → Mg(OH)2 + H2
1
2Mg(NO3)2 → 2MgO + 4NO2 + O2
1
(d) (i)
(ii)
[2]
[21]
© Cambridge International Examinations 2014
Page 4
Question
Mark Scheme
2
(a)
(b) (i)
(ii)
Mark Scheme
Cambridge International AS/A Level – October/November 2014
Syllabus
9701
Paper
21
Marks
Total
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
1
1
[2]
Very exothermic / gets very hot
OR creates (acid / H2SO4) spray / mist / fog / fumes
1
SO3 + H2SO4 → H2S2O7
1
H2S2O7 + H2O → 2H2SO4
1
(c) (i)
1
O
S
O
S
O
O
1+1
O
M1 SO2 correct M2 SO3 correct
(ii)
(d) (i)
(ii)
[2]
[2]
115–120° bent / non-linear
120° trigonal planar
1
1
Advantage = higher rate
Greater KE / energy / speed / collision frequency / proportion of successful collisions / more particles with E>Ea
1
1
Disadvantage – reduced yield / less product
1
(Forward reaction) exothermic AND (hence in accordance with LCP) equilibrium / reaction shifts left (to counteract
inc T) ora
1
Kp =
pSO3
[2]
[4]
2
1
2
pSO 2 × pO 2
© Cambridge International Examinations 2014
[1]
Page 5
Question
(iii)
Mark Scheme
Cambridge International AS/A Level – October/November 2014
Mark Scheme
Syllabus
9701
Paper
21
Marks
2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
2
2
0
(–1.8) (–0.9)
0.2
1.1
1.80
1
xSO3 = 1.8 / 3.1 = 0.581
xSO2 = 0.2 / 3.1 = 0.065
xO2 = 1.1 / 3.1 = 0.355
1
Kp =
Total
1
0.5812 × (2 × 105)2
= 1.13 × 10–3 Pa–1
5 2
5
0.065 × (2 × 10 ) × 0.355 × 2 × 10
2
1+1
[5]
[19]
3
(a)
(b) (i)
P; CH2 = C(CH3)2
Q; CH3CH2CH = CH2
R; CH3CH = CHCH3
S; (CH3)2CO
1
1
1
1
(Different molecules with) the same (molecular and) structural formula
1
different arrangements of atoms (in space) / different displayed formula
1
H
(ii)
H
C
H
C
C
H
H
H
H
C
H
trans-but-2-ene
H
H
C
HH
C
[4]
[2]
H
C
C
H
H
H
cis-but-2-ene
1
1
© Cambridge International Examinations 2014
[2]
Page 6
Question
(c)
Mark Scheme
Cambridge International AS/A Level – October/November 2014
Mark Scheme
Syllabus
9701
Paper
21
Marks
reagent; NaBH4 or LiA l H4 or names
1
product; propan-2-ol
1
Total
[2]
[10]
4
(a)
CH3CH2CO2H + 4[H] → CH3CH2CH2OH + H2O
(b) (i)
(ii)
1+1
[2]
Oxidation
1
[1]
Sodium / potassium dichromate or correct formula
H+ / acidified and (heat under) reflux
1
1
[2]
1+1
[2]
(c)
2 CH3CH2CO2H + CaCO3 → (CH3CH2CO2)2Ca + H2O + CO2
(d) (i)
CH3CO2H
1
warm / hot / high temperature / heat / reflux AND concentrated sulfuric acid
1
[2]
water (or hydrogen chloride or ethanoic acid)
1
[1]
(ii)
[10]
© Cambridge International Examinations 2014