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Cambridge IGCSE™
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CHEMISTRY0620/42
Paper 4 Theory (Extended) October/November 2021

 1 hour 15 minutes

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your name, centre number and candidate number in the boxes at the top of the page.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● Do not write on any bar codes.
● You may use a calculator.
● You should show all your working and use appropriate units.

INFORMATION
● The total mark for this paper is 80.
● The number of marks for each question or part question is shown in brackets [ ].
● The Periodic Table is printed in the question paper.

This document has 16 pages. Any blank pages are indicated.

IB21 11_0620_42/3RP
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1 This question is about states of matter.

(a) Complete the table, using ticks ( ) and crosses (  ), to describe the properties of gases, liquids
and solids.

particles particles have particles are

state of matter
are touching random movement regularly arranged

gas

liquid

solid

[3]

(b) Substances can change state.

(i) Boiling and evaporation are two ways in which a liquid changes into a gas.

Describe two differences between boiling and evaporation.

1 ...........................................................................................................................................

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

(ii) Name the change of state when:

● a gas becomes a liquid .................................................................................................

● a solid becomes a gas. .................................................................................................

[2]

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(c) A substance boils at temperature X and melts at temperature Y.

Complete the graph to show the change in temperature over time as the substance cools from
temperature A to temperature B.

temperature

time
[2]

(d) A solution is a mixture of a solute and a solvent.

(i) Name the process when a solid substance mixes with a solvent to form a solution.

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

(ii) Name the type of reaction when two solutions react to form an insoluble substance.

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

 [Total: 11]

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2 Acids are important laboratory chemicals.

(a) Some acids completely dissociate in water to form ions.

(i) State the term applied to acids that completely dissociate in water.

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

(ii) Complete the equation to show the complete dissociation of sulfuric acid in water.

H2SO4 → ..................................................................................... [2]

(iii) State the colour of methyl orange in sulfuric acid.

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

(b) The equation for the reaction between powdered zinc carbonate and dilute nitric acid is shown.

ZnCO3....... + 2HNO3....... → Zn(NO3)2....... + H2O....... + CO2.......

(i) Complete the equation by adding state symbols. [2]

(ii) A student found that 2.5 g of zinc carbonate required 20 cm3 of dilute nitric acid to react
completely.

Calculate the concentration of dilute nitric acid using the following steps:

● calculate the mass of 1 mole of ZnCO3

 .............................. g

● calculate the number of moles of ZnCO3 reacting

 .............................. moles

● determine the number of moles of HNO3 reacting

 .............................. moles

● calculate the concentration of HNO3.

 .............................. mol / dm3
[4]

 [Total: 10]

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3 Atoms contain protons, neutrons and electrons.

(a) Complete the table to show the relative mass and the relative charge of a proton, a neutron
and an electron.

relative mass relative charge

proton

neutron

1
electron 1840
[3]

(b) The table shows the number of protons, neutrons and electrons in some atoms and ions.

Complete the table.

atom number of number of number of

or ion protons neutrons electrons

16S
32

19K
39 +

35 44 36
[5]

 [Total: 8]

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4 Chlorine reacts with carbon monoxide to produce phosgene gas, COCl 2(g). A catalyst is used.

Cl 2(g) + CO(g) COCl 2(g)

The reaction is exothermic.

(a) Explain why the reaction is exothermic in terms of the energy changes of bond breaking and
bond making.

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

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

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

(b) (i) Complete the energy level diagram for this reaction.

On your diagram show:

● the product of the reaction

● an arrow representing the energy change, labelled ∆H
● an arrow representing the activation energy, labelled A.

Cl 2(g) + CO(g)
energy

progress of reaction
[3]

(ii) State why a catalyst is used.

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

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(c) Describe and explain the effect, if any, on the position of equilibrium when:

(i) the pressure is increased

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

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

(ii) the temperature is increased.

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

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

(d) The reaction between chlorine and carbon monoxide can be represented as shown.

O
Cl Cl + CO C
Cl Cl

When one mole of chlorine reacts with one mole of carbon monoxide, 230 kJ of energy is
released.

Some bond energies are shown in the table.

bond bond energy in kJ / mol

Cl –Cl 240
C=O 745
C–Cl 400

Use the information to calculate the energy of the bond between the C and the O in
carbon monoxide, CO.

 bond energy in carbon monoxide, CO = .............................. kJ / mol [3]

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(e) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of COCl 2.

C
Cl Cl

Show outer electrons only.

Cl Cl

[3]

 [Total: 17]

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5 Iron is a transition element. Potassium is a Group I element.

(a) Iron and potassium have the same type of bonding.

Name and describe the type of bonding in these two elements.

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

description ..................................................................................................................................

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

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

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

(b) Transition elements and Group I elements have some similar physical properties.

They can both:

●  e hammered into a shape

b
● conduct electricity
● be stretched into wires.

(i) Name the term used to describe the ability of elements to be hammered into a shape.

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

(ii) Describe what happens to the particles in iron when it is hammered into a shape.

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

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

(iii) Suggest why copper, rather than other transition elements, is used for wires which conduct
electricity.

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

(c) Transition elements are harder and stronger than Group I elements.

Describe how two other physical properties of transition elements are different from those of
Group I elements.

1 ..................................................................................................................................................

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

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(d) Chemical properties of some Group I elements are shown in the table.

flame test
element reaction with cold water reaction with oxygen
colour
● steadily effervesces
lithium very slowly forms an oxide layer red
● forms a colourless solution
● strongly effervesces
sodium slowly forms an oxide layer
● forms a colourless solution
● v ery strongly effervesces
potassium quickly forms an oxide layer
● forms a colourless solution

rubidium ruby red

(i) Add to the table:

● the flame test colours for sodium and potassium

● the predicted reactions of rubidium with water and with oxygen.
[4]

(ii) Name the gas produced when Group I elements react with water.

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

(iii) Name the solution formed when potassium reacts with water.

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

(iv) Predict the pH of the colourless solution formed when potassium reacts with water.

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

(v) Write the chemical equation for the reaction of sodium with oxygen.

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

(e) Iron is a typical transition element. It is the catalyst used in the Haber process.

(i) Write the equation for the reaction that occurs in the Haber process.

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

(ii) State the temperature and pressure used in the Haber process. Include units.

temperature .........................................................................................................................

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

 [Total: 22]

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6 Ethanol, C2H5OH, belongs to the homologous series called alcohols.

(a) Write the general formula of alcohols.

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

(b) Explain why ethanol cannot be described as a hydrocarbon.

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

(c) Ethanol can be manufactured from different substances by reaction with steam or by
fermentation.

(i) Give the formula of the substance which reacts with steam to form ethanol.

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

(ii) Name a substance which will undergo fermentation to form ethanol.

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

(d) Ethanol is a fuel.

Write the chemical equation for the complete combustion of ethanol.

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

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(e) Ethane-1,2-diol has two alcohol functional groups.

H H

H O C C O H

H H

One molecule of ethane-1,2-diol will react with two molecules of ethanoic acid to form
molecule X.

X has two ester functional groups and a molecular formula of C6H10O4.



(i) State the empirical formula of X.

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

(ii) Draw the structure of X.

Show all of the atoms and all of the bonds.

[2]

(iii) Name the other substance formed in this reaction.

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

(f) Each alcohol functional group in ethane-1,2-diol reacts with acidified potassium manganate(VII)
to form a different organic compound, Y.

(i) Name the functional groups formed in Y.

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

(ii) Draw the structure of Y.

Show all of the atoms and all of the bonds.

[1]

 [Total: 12]

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Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every
reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the
publisher will be pleased to make amends at the earliest possible opportunity.

To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge
Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download
at www.cambridgeinternational.org after the live examination series.

Cambridge Assessment International Education is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of the University of
Cambridge Local Examinations Syndicate (UCLES), which itself is a department of the University of Cambridge.

© UCLES 2021 0620/42/O/N/21

 The Periodic Table of Elements
Group

© UCLES 2021
I II III IV V VI VII VIII
1 2

H He
hydrogen helium
Key 1 4
3 4 atomic number 5 6 7 8 9 10

Li Be atomic symbol B C N O F Ne
lithium beryllium name boron carbon nitrogen oxygen fluorine neon
7 9 relative atomic mass 11 12 14 16 19 20
11 12 13 14 15 16 17 18

Na Mg Al Si P S Cl Ar
sodium magnesium aluminium silicon phosphorus sulfur chlorine argon
23 24 27 28 31 32 35.5 40
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton
39 40 45 48 51 52 55 56 59 59 64 65 70 73 75 79 80 84
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon
16

85 88 89 91 93 96 – 101 103 106 108 112 115 119 122 128 127 131
55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

0620/42/O/N/21
lanthanoids
Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon
133 137 178 181 184 186 190 192 195 197 201 204 207 209 – – –
87 88 89–103 104 105 106 107 108 109 110 111 112 114 116
actinoids
Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Fl Lv
francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium flerovium livermorium
– – – – – – – – – – – – –

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71
lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium
139 140 141 144 – 150 152 157 159 163 165 167 169 173 175
89 90 91 92 93 94 95 96 97 98 99 100 101 102 103
actinoids Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium
– 232 231 238 – – – – – – – – – – –
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The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.).