Mark Scheme

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UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS
GCE Ordinary Level

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MARK SCHEME for the May/June 2011 question paper for the guidance of teachers

5070 CHEMISTRY
5070/21 Paper 2 (Theory), maximum raw mark 75

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 must be read in conjunction with the question papers and the report on the examination.

• Cambridge will not enter into discussions or correspondence in connection with these mark schemes.

Cambridge is publishing the mark schemes for the May/June 2011 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2

Mark Scheme: Teachers’ version GCE O LEVEL – May/June 2011

Syllabus 5070

Paper 21

A1 Allow correct name but formula takes precedence (a) V2O5 (1) (b) ZnSO4 (1) (c) AgI (1) (d) CF3Cl3 (1) (e) (NH4)2SO4 / ZnSO4 (1) (f) CH4 (1) (g) (NH4)2SO4 (1) [1] [1] [1] [1] [1] [1] [1] [Total: 7] A2 (a) sulfur dioxide (1) Allow SO2 (b) copper(II) sulfate (1) Allow CuSO4 (c) H+ + OH– → H2O (1) Ignore state symbols (d) (i) Copper(II) hydroxide (1) Allow Cu(OH)2 (ii) Cu2+(aq) + 2OH–(aq) → Cu(OH)2(s) Balanced equation (1) Correct state symbols (1)

[1]

[1]

[1]

[1]

[2]

(e) Mol ratio Cu:O = CuO (1)

79.9 20.1 : / 1.25 : 1.26 (1) 64 16
[2] [Total: 8]

© University of Cambridge International Examinations 2011

Page 3

Mark Scheme: Teachers’ version GCE O LEVEL – May/June 2011

Syllabus 5070

Paper 21 [1] [1]

A3 (a) (i) same number of electrons / same number of protons / same electronic arrangement of electrons / both have 92 electrons / both have 92 protons (1) (ii) different number of neutrons / uranium-238 has three more neutrons (1) (b) (i) UO2 + 4HF → UF4 + 2H2O (1) (ii) UF4 + 2Mg → U + 2MgF2 (1)

[1] [1]

(iii) reaction involving gain of electrons / reaction involving decrease in oxidation number (1) Allow a reaction involving the loss of oxygen / gain of hydrogen [1] (iv) Mr of UO2 = 270 (1) Moles of UO2 = 3704 (1) Allow ecf from wrong Mr Mass of uranium = 0.881 tonnes (1) Allow ecf from wrong moles Correct answer scores all three marks OR Alternative approach using percentage composition Mr of UO2 = 270 (1) % of U = 88.1% (1) Allow ecf from wrong Mr Mass of uranium = 0.881 tonnes (1) Allow ecf from wrong percentage (c) between magnesium and copper (1)

[3] [1] [Total: 9]

© University of Cambridge International Examinations 2011

Page 4

Mark Scheme: Teachers’ version GCE O LEVEL – May/June 2011

Syllabus 5070

Paper 21

A4 (a) All covalent bond pairs shown (1) Rest of structure correct (1) Ignore inner shell electrons of oxygen (b) Must be a comparison in both marking points Particles in a gas are moving faster than particles in a liquid (1) Particles in a gas are further apart than those in a liquid (1)

[2]

[2]

(c) Particles in pure hydrogen peroxide are more crowded / closer together / more particles per unit volume / particles are more concentrated (1) So more collisions per second / increased collision frequency / collisions more often / more chance of collision / collisions more likely (1) [2] (d) (i) Fe2+ → Fe3+ + e– (1) Allow Fe2+ – e– → Fe3+ Allow e instead of e–

[1]

(ii) Add sodium hydroxide (solution) / (aqueous) Ammonia / add (aqueous) hydroxide ions (1) Should be a brown-rust ppt (1) [2] (e) (Colour change of KMnO4 shows) it is a reducing agent / it can be oxidised (1) (Colour change of KI shows) it is an oxidising agent / it can be reduced (1)

[2] [Total: 11]

A5 (a) 78–79 % (1) (b) Fractional distillation (1) of liquid...
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