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CAMBRIDGE INTERNATIONAL EXAMINATIONS

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GCE Advanced Subsidiary Level and GCE Advanced Level

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MARK SCHEME for the May/June 2013 series

9701 CHEMISTRY
9701/23 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 May/June 2013 series for most IGCSE, GCE
Advanced Level and Advanced Subsidiary Level components and some Ordinary Level components.
 Page 2 Mark Scheme Syllabus Paper
GCE AS/A LEVEL – May/June 2013 9701 23

1 (a) (i)

S C S

S atom has 6 and C atom has 4 electrons (1)

S=C double bonds (4 electrons) clearly shown (1)

(ii) linear and 180° (1) [3]

(b) (i) CS2 + 3O2 → CO2 + 2SO2 (1)

(ii) enthalpy change when 1 mol of a substance (1)

is burnt in an excess of oxygen/air

or is completely combusted

under standard conditions (1) [3]

(c)
CS2 + 3O2 → CO2 + 2SO2
–1
∆Hf /kJ mol x
⦵ –395 2(–298) (1)
∆Hreaction = –395 + 2(–298) – x = –1110 kJ mol–1 (1)
gives x = –395 + (–596) + 1110 = +119 kJ mol–1 (1) [3]

(d) (i) CS2 + 2NO → CO2 + 2S + N2

or
CS2 + 2NO → CO + 2S + N2O

correct products (1)

correct equation (1)

(ii) from –2 to 0 both required (1) [3]

[Total: 12]

© Cambridge International Examinations 2013

 Page 3 Mark Scheme Syllabus Paper
GCE AS/A LEVEL – May/June 2013 9701 23

2 (a) (i) if the conditions of a system in equilibrium are changed (1)

the position of equilibrium moves so as to reduce that change (1) [2]

(ii) lower temperature (1)

because the forward reaction is exothermic (1)

higher pressure (1)

because the forward reaction shows a reduction in volume

or
there are fewer molecules/moles on RHS of equilibrium (1) [4]

(b) CO2 + H2 ⇌ CO + H2O

initial moles 0.70 0.70 0.30 0.30

equil. moles (0.70–x) (0.70–x) (0.30+x) (0.30+x) (1)

equil. concn. (0.70–x) (0.70–x) (0.30+x) (0.30+x)

1 1 1 1

Kc = (0.30+x)2 = 1.44 (1)

(0.70-x)2

gives x = 0.25 (1)

at equilibrium,
n(CO2) = n(H2) = 0.70 – 0.25 = 0.45 moles
and
n(CO) = n(H2O) = 0.3 + 0.25 = 0.55 moles (1) [4]

[Total: 10]

© Cambridge International Examinations 2013

 Page 4 Mark Scheme Syllabus Paper
GCE AS/A LEVEL – May/June 2013 9701 23

3 (a) (i) He or Ne or Ar or Kr (1)

(ii) P or As (1)

(iii) Br (1)

(iv) Na allow Ar (1)

(v) Si (1)

(vi) P allow Si (1)

(vii) Cl or F or Br (1) [7]

(b) (i) any two from P4O6, SO2 and Cl2O7 (1+1)

(ii) Al2O3 or SiO2 (1)

(iii) MgSO3 (1) [4]

(c) (i) Si is giant molecular/giant covalent or

P, S, and Cl are simple molecular (1)

(ii) the molecules are S8, P4, Cl2 (1)

larger molecules have more electrons (1)

and hence greater van der Waals' forces (1) [4]

[Total: 15]

© Cambridge International Examinations 2013

 Page 5 Mark Scheme Syllabus Paper
GCE AS/A LEVEL – May/June 2013 9701 23

4 (a) (i)
CH3(CH2)4COCH3

reduce

CH3(CH2)4CH(OH)CH3

dehydrate

CH3(CH2)4CH=CH2 CH3(CH2)3CH=CHCH3

S T

one mark for each correct compound, R, S and T

allow correct cis and trans versions of compound T for 2 marks (3 × 1)

(ii) reduction

NaBH4 or LiAlH4 or H2/Ni or Na/C2H5OH (1)

dehydration

P4O10/P2O5 or H3PO4 or conc. H2SO4 or Al2O3 (1) [5]

(b)

Tollens’ reagent NO REACTION

CH3(CH2)4C(OH)CH3
HCN 
CN

K2Cr2O7/H+ NO REACTION

one mark for each correct answer (3 × 1) [3]

© Cambridge International Examinations 2013

Page 6 Mark Scheme Syllabus Paper
GCE AS/A LEVEL – May/June 2013 9701 23

(c) Na2CO3 or NaHCO3 effervescence/colourless gas

or
Na colourless gas
or
PCl3/PCl5 etc. steamy fumes
or
C2H5OH/conc. H2SO4 sweet smell of ester
or
K2Cr2O7/H+ orange solution becomes green

correct reagent (1)

correct observation (1) [2]

[Total: 10]

© Cambridge International Examinations 2013

 Page 7 Mark Scheme Syllabus Paper
GCE AS/A LEVEL – May/June 2013 9701 23

5 (a) (i) CH2=CHCO2H (1)

(ii) BrCH2CHBrCH2OH (1)

(iii) product is HOCH2CH(OH)CH2OH

correct addition across >C=C< (1)

original –CH2OH remains (1)

(iv) HO2CCO2H (1) [5]

(b) (i) nucleophilic substitution (1)

(ii) oxidation (1) [2]

(c) (i) step I

H2 (1)

heat with Ni catalyst (1)

step II

acidified K2Cr2O7 (1)

heat or distil off product (1)

(ii) structural isomerism

or
functional group isomerism (1) [5]

(d) both oxidation and reduction have occurred or

disproportionation has taken place (1) [1]

[Total: 13]

© Cambridge International Examinations 2013