w
w
ap
eP
m
e
tr
.X
w
CAMBRIDGE INTERNATIONAL EXAMINATIONS
9701 CHEMISTRY
9701/21
Paper 2 (Structured Questions AS Core),
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 May/June 2014 series for most IGCSE, GCE
Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.
om
.c
MARK SCHEME for the May/June 2014 series
s
er
GCE Advanced Subsidiary Level and GCE Advanced Level
Page 2
Mark Scheme
GCE AS/A LEVEL – May/June 2014
Syllabus
9701
Paper
21
Question
Mark Scheme
1
The amount of energy required / energy change / enthalpy change when one electron is
removed
from each atom / (cat)ion in one mol
of gaseous atoms / (cat)ions
OR energy change when 1 mole of electrons is removed from one mole of gaseous
atoms / ions
X(g) → X+(g) + e– gains 2 marks
1
Group V / 5 / 15
1
Big difference between fifth and sixth ionisation energies
1
2
1s2 2s2 2p3
ecf from (b)(i) if period 2
1
1
(Weighted) mean / average mass of an atom(s) (of an element)
1
Relative to 1 / 12th of (the mass of an atom of) carbon-12 OR
relative to carbon-12 which is (exactly) 12 (units)
allow as an expression
1
(a)
(b) (i)
(ii)
(c) (i)
(ii)
Z
31.13
Ar
So
Mark
Total
1
1
3
2
Cl
68.87
= 1: 2
35.5
68.87/35.5
=2
31.13/Ar
1
2 × 31.13 × 35.5
= 32.0923 = 32.1 to 3s.f.
68.87
Allow alternative correct methods
Ar =
© Cambridge International Examinations 2014
1
2
Page 3
Question
(d) (i)
Mark Scheme
GCE AS/A LEVEL – May/June 2014
Mark Scheme
Syllabus
9701
Paper
21
Mark
NaCl (+ aq ) NaCl + H2O Na+ + Cl –
Na+ + Cl – + H2O
1
SiCl 4 + 2H2O SiCl 4 + 4H2O SiCl 4 + 4H2O SiO2 + 4HCl
Si(OH)4 + 4HCl
SiO2.2H2O + 4HCl
1
2
Allow correct equation with other molar amounts of water
(ii)
(e)
Total
NaCl is ionic AND giant / lattice
NaCl dissolves / does not react
SiCl 4 is covalent AND molecular / simple
SiCl 4 is hydrolysed / reacts
1
1
1
1
4
shape of SF6 = Octahedral
bond angle = 90°
1
1
2
18
2
(a) (i)
(ii)
(b) (i)
(ii)
(The MnO4‒ ions cause the Fe2+ ions to) lose electrons owtte / ora
MnO4–(aq) + 5Fe2+(aq) + 8H+(aq) Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)
20.0 × 0.020 = 4(.00) ×10 − 4 (mol)
1000
MnO4– : Fe2+ = 1 : 5
so amount of Fe2+ = 5 × 4.00 × 10‒4 = 2(.00) × 10‒3 (mol)
1
1
1+1+1
3
1
1
1
1
1
1
ecf from (b)(i)
(iii)
2.00 × 10‒3 × 250 / 25 = 0.02(00) (mol)
ecf from (b)(ii)
© Cambridge International Examinations 2014
Page 4
Question
Mark Scheme
GCE AS/A LEVEL – May/June 2014
Syllabus
9701
Mark Scheme
Paper
21
Mark
Total
(iv)
3.40 / 0.02 = 170
ecf from (b)(iii)
1
1
(v)
170 – 151.8 = 18.2
18.2 / 18 = 1.01
x=1
ecf from (b)(iv) if appropriate
1
1
9
3
(a) (i)
(ii)
K = Cl– / chloride / F– / fluoride
1
H2SO4 + 2NaCl Na2SO4 + 2HCl (or equation with F or K for Cl) OR
H2SO4 + NaCl NaHSO4 + HCl (or equation with F or K for Cl )
1
ecf from identity of K so long as halide
HK is acidic / HK is a gas / an acidic gas is produced
1
L = I– / iodide
1
colour = yellow
ecf from identity of L i.e. Cl – (white) or Br– (cream)
1
Ag+ + I‒ AgI (or equation with L)
AgNO3 + NaI → AgI + NaNO3 (or equation with L)
ecf from identity of L so long as halide
(iii)
(b) (i)
3
3
1
Br2 / bromine has fewer electrons than iodine / more electrons than chlorine
intermolecular / van der Waals’ forces (in Br2 / M2) weaker than in iodine / stronger than
in chlorine
1
1
2
B = chlorine / Cl 2
C = hydrogen / H2
D = sodium hydroxide / NaOH
1
1
1
3
© Cambridge International Examinations 2014
Page 5
Question
(ii)
Mark Scheme
GCE AS/A LEVEL – May/June 2014
Mark Scheme
Syllabus
9701
Paper
21
Mark
anode: 2Cl – Cl 2 + 2e–
1
cathode: 2H+ + 2e– H2 OR
2H2O + 2e– 2OH– + H2
1
Total
2
13
4
(a)
decolourisation with an alkene at room conditions / quickly / easily /
OR alkane needs higher temp / UV / is slow at room conditions
1
double / π / pi bond / C = C present in alkenes
1
2
UV light / sunlight / high temperature
1
1
(Free) radical
Substitution
1
1
2
(iii)
•C2H5 + •C2H5 C4H10
1
1
(iv)
C2H5Br + Br• •C2H4Br + HBr OR
•C2H4Br + Br2 C2H4Br2 + Br•
1
1
Electrophilic
Addition
1
1
2
(b) (i)
(ii)
(c) (i)
© Cambridge International Examinations 2014
Page 6
Question
Mark Scheme
GCE AS/A LEVEL – May/June 2014
Syllabus
9701
Mark Scheme
(ii)
H
Mark
H
H
H C
C H
Br
Paper
21
H
C
Br
δ+
H
+
C
H
-
H
H
H
C
C
H
Br Br
Br
Br δ−
M3:
M3: Correct
correctintermediate
intermediate
M1:
M1:22correct
correctcurly
curly
arrows
arrows
M4: Curly arrow from
+
−
M4: curly
C+ lone pair on Br to C
lone
pair onarrow
Br− tofrom
M2: dipole
M2: correct dipole
(d)
H
Total
4
H
H
H
H
H
H
C
C
C
C
C
C
H
Cl
H
Cl
H
Cl
H
2
2
minimum of three repeat units
(e) (i)
(ii)
NaOH/KOH
1
ethanolic / alcoholic AND heat / reflux
1
2
1
1
H
H
H OH
(iii)
N
C
H
H
C
C
H
H
1
H
Propanenitrile / propanonitrile / propionitrile / ethyl cyanide / cyanoethane
1
2
20
© Cambridge International Examinations 2014