Cambridge International Examinations

Cambridge International General Certificate of Secondary Education

*1845295131*

CHEMISTRY 0620/32
Paper 3 (Extended) October/November 2014
1 hour 15 minutes
Candidates answer on the Question Paper.
No Additional Materials are required.

READ THESE INSTRUCTIONS FIRST

Write your Centre number, candidate number and name on all the work you hand in.
Write in dark blue or black pen.
You may use an HB pencil for any diagrams or graphs.
Do not use staples, paper clips, glue or correction fluid.
DO NOT WRITE IN ANY BARCODES.

Answer all questions.

Electronic calculators may be used.
A copy of the Periodic Table is printed on page 16.
You may lose marks if you do not show your working or if you do not use appropriate units.

At the end of the examination, fasten all your work securely together.
The number of marks is given in brackets [ ] at the end of each question or part question.

The syllabus is approved for use in England, Wales and Northern Ireland as a Cambridge International Level 1/Level 2 Certificate.

This document consists of 13 printed pages and 3 blank pages.

IB14 11_0620_32/2RP
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1 An important aspect of chemistry is purity and methods of purification.

(a) Give an example of substances used in everyday life which must be pure.

.............................................................................................................................................. [1]

(b) A list of techniques used to separate mixtures is given below.

chromatography crystallisation diffusion dissolving

evaporation filtration fractional distillation simple distillation

(i) From the list, choose the most suitable technique to separate the following.

water from sea-water ..........................................................................................................

helium from a mixture of helium and methane ...................................................................

ethanol from a mixture of ethanol and propanol .................................................................

iron filings from a mixture of iron filings and water .............................................................

a mixture of two amino acids, glycine and alanine .............................................................

[5]

(ii) Describe how you would obtain a pure sample of copper(II) sulfate-5-water crystals from
a mixture of copper(II) sulfate-5-water with copper(II) oxide using some of the techniques
listed above.

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [4]

[Total: 10]

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2 Aluminium is obtained by the reduction of aluminium ions to aluminium atoms.

(a) Write an ionic equation for the reduction of an aluminium ion to an aluminium atom.

.............................................................................................................................................. [2]

(b) The original method of extracting aluminium involved the reduction of aluminium chloride using
the reactive metal sodium. Aluminium obtained by this method was very expensive due to the
high cost of extracting sodium from sodium chloride.

(i) Complete the equation for this reduction.

Al Cl 3 + .......Na → ........... + ...........

[2]

(ii) How can sodium metal be obtained from sodium chloride?

.............................................................................................................................................

....................................................................................................................................... [2]

(c) In the modern method, aluminium is obtained by the electrolysis of aluminium oxide (alumina)
dissolved in molten cryolite, Na3Al F6.

waste gases,
O2, CO2, CO, F2

carbon anode (+)

mixture of aluminium
carbon cathode (–) oxide and cryolite

molten aluminium

(i) The major ore of aluminium is impure aluminium oxide.

What is the name of this ore?

....................................................................................................................................... [1]

(ii) This ore is a mixture of aluminium oxide, which is amphoteric, and iron(III) oxide which is
basic.
Explain how these two oxides can be separated by the addition of aqueous sodium
hydroxide.

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [2]

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(iii) Give two reasons why the electrolyte contains cryolite.

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [2]

(iv) The mixture of gases evolved at the positive electrode includes:

carbon dioxide
carbon monoxide
fluorine
oxygen

Explain the presence of these gases in the gaseous mixture formed at the positive
electrode. Include at least one equation in your explanation.

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [5]

(d) A major use of aluminium is the manufacture of pots and pans. One reason for this is its
resistance to corrosion.

(i) Explain why aluminium, a reactive metal, is resistant to corrosion.

.............................................................................................................................................

....................................................................................................................................... [1]

(ii) Suggest two other reasons why aluminium is suitable for making pots and pans.

.............................................................................................................................................

....................................................................................................................................... [2]

[Total: 19]

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3 (a) A hydrocarbon has the following structural formula.

H H

H C C H

H C C H
H H

(i) State the molecular formula and the empirical formula of this hydrocarbon.

molecular formula ...............................................................................................................

empirical formula ................................................................................................................

[2]

(ii) Draw the structural formula of an isomer of the above hydrocarbon.

[1]

(iii) Explain why these two hydrocarbons are isomers.

.............................................................................................................................................

....................................................................................................................................... [2]

(iv) Are these two hydrocarbons members of the same homologous series?
Give a reason for your choice.

.............................................................................................................................................

....................................................................................................................................... [1]

(b) Alkenes can be made from alkanes by cracking.

(i) Explain the term cracking.

.............................................................................................................................................

....................................................................................................................................... [2]

(ii) One mole of an alkane, when cracked, produced one mole of hexane, C6H14, and two
moles of ethene.
What is the molecular formula of the original alkane?

....................................................................................................................................... [1]

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(c) Alkenes are used in polymerisation reactions and addition reactions.

(i) Draw the structural formula of the product formed by the addition polymerisation of
but-2-ene. Its formula is given below.

H H

C C

H 3C CH3

[3]

(ii) Give the name and structural formula of the addition product formed from ethene and
bromine.

name ...................................................................................................................................

structural formula

[2]

[Total: 14]

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4 Zinc is an important metal. Its uses include making alloys and the construction of dry cells (batteries).

(a) Name an alloy which contains zinc. What is the other metal in this alloy?

name of alloy .............................................................................................................................

other metal in alloy ....................................................................................................................

[2]

(b) The main ore of zinc is zinc blende, ZnS.

(i) The ore is heated in the presence of air to form zinc oxide and sulfur dioxide.
Write the equation for this reaction.

....................................................................................................................................... [2]

(ii) Give a major use of sulfur dioxide.

....................................................................................................................................... [1]

(c) Zinc can be obtained from zinc oxide in a two step process. Aqueous zinc sulfate is made from
zinc oxide and then this solution is electrolysed with inert electrodes. The electrolysis is similar
to that of copper(II) sulfate with inert electrodes.

(i) Name the reagent which will react with zinc oxide to form zinc sulfate.

....................................................................................................................................... [1]

(ii) Complete the following for the electrolysis of aqueous zinc sulfate.

Write the equation for the reaction at the negative electrode.

.............................................................................................................................................

Name the product at the positive electrode.

.............................................................................................................................................

The electrolyte changes from zinc sulfate to .................................................................... .

[3]

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(d) A dry cell (battery) has a central rod, usually made of graphite. This is the positive electrode which
is surrounded by the electrolyte, typically a paste of ammonium chloride and manganese(IV)
oxide, all of which are in a zinc container which is the negative electrode.

wire
electrons flow
graphite
when cell
electrode
produces
energy
zinc
electrode

electrolyte which is a paste of

ammonium chloride
and manganese(IV) oxide

(i) Draw an arrow on the diagram to indicate the direction of electron flow. [1]

(ii) Suggest why the electrolyte is a paste.

....................................................................................................................................... [1]

(iii) The following changes occur in a dry cell.

For each change, decide if it is oxidation or reduction and give a reason for your choice.

Zn to Zn2+

.............................................................................................................................................

manganese(IV) oxide to manganese(III) oxide

.............................................................................................................................................
[2]

[Total: 13]

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5 (a) Glucose, sucrose and starch are all carbohydrates. Their formulae are:

glucose, C6H12O6,
sucrose, C12H22O11,
starch, (C6H10O5)n.

(i) Identify two common features in the formulae of these carbohydrates.

.............................................................................................................................................

....................................................................................................................................... [2]

(ii) Draw the structure of a complex carbohydrate, such as starch. The formula of glucose,
can be represented by
HO OH

Include three glucose units in the structure.

[2]

(b) Starch hydrolyses to glucose in the presence of the enzyme, amylase.

What is meant by the term enzyme?

.............................................................................................................................................. [2]

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(c) The effect of temperature on this reaction can be studied by the experiment shown below.
Starch and iodine form a blue-black colour.
Glucose and iodine do not form a blue-black colour.

teat pipette to add a

few drops of iodine

water at different
temperatures

aqueous starch and

amylase (enzyme)

The experiment is set up as in the diagram and the time measured for the mixture to change
from blue-black to colourless. The experiment is repeated at different temperatures.
Typical results of this experiment are given in the table below.

time for blue-black

temperature
experiment colour to disappear
/ °C
/ min

A 20 30
B 40 15
C 70 remained blue-black

(i) Put the experiments in order of reaction rate – slowest first and fastest last.

....................................................................................................................................... [2]

(ii) Explain why the reaction rates in experiments A and B are different.

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [3]

(iii) Suggest why the colour remains blue-black in experiment C.

....................................................................................................................................... [1]

[Total: 12]

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6 Sulfuric acid is an important acid, both in the laboratory and in industry.

Sulfuric acid is manufactured in the Contact Process. Originally, it was made by heating metal
sulfates and by burning a mixture of sulfur and potassium nitrate.

(a) Give a major use of sulfuric acid.

.............................................................................................................................................. [1]

(b) A group of naturally occurring minerals have the formula of the type FeSO4.xH2O where x is 1,
4, 5, 6 or 7. The most common of these minerals is iron(II) sulfate-7-water.

(i) When this mineral is heated gently it dehydrates.

FeSO4.7H2O FeSO4 + 7H2O

green pale yellow

Describe how you could show that this reaction is reversible.

.............................................................................................................................................

.............................................................................................................................................

....................................................................................................................................... [2]

(ii) When the iron(II) sulfate is heated strongly, further decomposition occurs.

2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g)

The gases formed in this reaction react with water and oxygen to form sulfuric acid.
Explain how the sulfuric acid is formed.

.............................................................................................................................................

....................................................................................................................................... [2]

(iii) A mineral of the type FeSO4.xH2O contains 37.2% of water.

Complete the calculation to determine x.

mass of one mole of H2O = 18 g

mass of water in 100 g of FeSO4.xH2O = 37.2 g

number of moles of H2O in 100 g of FeSO4.xH2O = .................

mass of FeSO4 in 100 g of FeSO4.xH2O = ................. g

mass of one mole of FeSO4 = 152 g

number of moles of FeSO4 in 100 g of FeSO4.xH2O = .................

x = .................
[4]

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(c) When a mixture of sulfur and potassium nitrate is burned and the products are dissolved in
water, sulfuric acid is formed.

(i) The sulfuric acid formed by this method is not pure. It contains another acid.
Deduce the identity of this acid.

....................................................................................................................................... [1]

(ii) The heat causes some of the potassium nitrate to decompose.

Write the equation for the action of heat on potassium nitrate.

....................................................................................................................................... [2]

[Total: 12]

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© UCLES 2014
DATA SHEET
The Periodic Table of the Elements
Group
I II III IV V VI VII 0
1 4
H He
Hydrogen Helium
1 2

7 9 11 12 14 16 19 20
Li Be B C N O F Ne
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
3 4 5 6 7 8 9 10

23 24 27 28 31 32 35.5 40
Na Mg Al Si P S Cl Ar
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
11 12 13 14 15 16 17 18

39 40 45 48 51 52 55 56 59 59 64 65 70 73 75 79 80 84

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

publisher will be pleased to make amends at the earliest possible opportunity.

Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
16

85 88 89 91 93 96 101 103 106 108 112 115 119 122 128 127 131
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

0620/32/O/N/14
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

133 137 139 178 181 184 186 190 192 195 197 201 204 207 209
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Caesium Barium Lanthanum Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine Radon
55 56 57 * 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

226 227

Fr Ra Ac
Francium Radium Actinium
87 88 89

140 141 144 150 152 157 159 162 165 167 169 173 175
*58-71 Lanthanoid series
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
90-103 Actinoid series Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium
58 59 60 61 62 63 64 65 66 67 68 69 70 71
a a = relative atomic mass 232 238
Key X X = atomic symbol Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium
b b = proton (atomic) number 90 91 92 93 94 95 96 97 98 99 100 101 102 103

The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.).

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