Chemistry 0620/31 May/June 2021: question paper and mark scheme
Cambridge IGCSE Chemistry (0620), Paper 3 Theory (Core), May/June 2021. Read both free below, or download them. Done the paper? Get it marked by AI against this mark scheme.
(a) The electronic structures of five atoms, A, B, C, D and E, are shown.
A B C D E
Answer the following questions about these electronic structures.
Each electronic structure may be used once, more than once or not at all.
State which electronic structure, A, B, C, D or E, represents:
(i) an atom in Group II of the Periodic Table
. …… [1]
(ii) an atom with a proton number of 13
. …… [1]
(iii) an atom that forms a stable ion with a single negative charge
. …… [1]
(iv) an atom of a non-metal that forms a giant covalent structure
. …… [1]
(v) an atom of a metal used in food containers.
. …… [1]
(b) Complete the table to show the number of electrons, neutrons and protons in the vanadium atom and calcium ion shown.
number of number of number of electrons neutrons protons
23V
51
23
20Ca
48 2+
28
[3]
[Total: 8]
Mark scheme
1(a)(i) C 1
1(a)(ii) D 1
1(a)(iii) E 1
1(a)(iv) B 1
1(a)(v) D 1
1(b) number of electrons in Ca ion: = 18 (1) 3
number of neutrons in V = 28 (1)
number of protons in V = 23
AND
number of protons in Ca ion = 20 (1)
The table shows the masses of some of the ions in 1000 cm3 of fruit juice.
mass of ion in 1000 cm3 name of ion formula of ion of fruit juice / mg
NH4+ 43 calcium Ca2+ 79 chloride Cl – 135 lithium Li+ 1 magnesium Mg2+ 80 nitrate NO3– 35 phosphate PO43– 120 potassium K+ 575 sodium Na+ 120
SO42– 105
(a) Answer these questions using only the information in the table.
(i) State which negative ion has the highest mass in 1000 cm3 of fruit juice.
. …… [1]
(ii) Give the formulae of the ions in ammonium sulfate.
…… and . …… [1]
(iii) Calculate the mass of sodium ions in 200 cm3 of fruit juice.
mass = …… mg [1]
(b) Describe a test for lithium ions.
test . ……
observations ……
[2]
(c) Ions of the element potassium, K, are present in most fertilisers.
State the names of two other elements that are in most fertilisers.
1 ……
2 ……
[2]
(d) Orange juice is acidic.
Draw a circle around the pH of orange juice.
pH 4 pH 7 pH 10 pH 13[1]
(e) Some soils are acidic.
Give the names of two compounds that are used to make soils less acidic.
1 ……
2 ……
[2]
(f) Hydrogen chloride is an acidic gas produced when concentrated hydrochloric acid evaporates.
(i) Describe the arrangement and separation of the molecules in hydrogen chloride gas.
arrangement ……
. ……
separation . ……
. ……
[2]
(ii) A long glass tube is set up as shown.
long glass tube
cotton wool soaked in damp blue litmus paper concentrated hydrochloric acid
At first, the blue litmus paper does not turn red.
After a short time, the litmus paper turns red.
Explain these observations using the kinetic particle model.
. ……
. ……
. ……
. ……
. …… [3]
[Total: 15]
Mark scheme
2(a)(i) Cl – / chloride 1
2(a)(ii) NH4+ AND SO42- 1
2(a)(iii) 24 (mg) 1
2(b) flame test / description of flame test (1) 2
(flame coloured) red (1)
2(c) nitrogen (1) 2
phosphorus (1)
pH 4 circled 1
2(e) 1 mark each for any 2 of: 2
• calcium carbonate
• calcium oxide
• calcium hydroxide
2(f)(i) arrangement: random (arrangement) / no fixed arrangement / no pattern / no fixed position (1) 2
separation: far apart / far away (from each other) / distant (from each other) (1)
2(f)(ii) 1 mark each for any 3 of: 3
• (HCl) molecules escape from solution
• diffusion
• molecules in (constant) movement / molecules collide / molecules travel
• (movement of) molecules is random / haphazard / in every direction
• molecules spread out / molecules mix
• (molecules spread) from high(er) concentration to low(er) concentration
• molecules hit the litmus paper / molecules
The table shows some properties of four Group I elements.
melting point boiling point atomic radius element
/ °C / °C / nm
sodium 98 883 0.191
potassium 63 760
rubidium 39 0.250
caesium 29 671 0.272
(a) (i)
Complete the table by predicting:
● the boiling point of rubidium
● the atomic radius of potassium.
[2]
(ii) Describe the trend in the melting point of the Group I elements down the group.
. …… [1]
(iii) Deduce the physical state of potassium at 60 °C.
Explain your answer.
. ……
. ……
. …… [2]
(b) Caesium is a radioactive element with a proton number of 55.
(i) Define proton number.
. …… [1]
(ii) State one industrial use of radioactive isotopes.
. …… [1]
(c) Sodium hydride, NaH, reacts with iron(III) oxide.
(i) Balance the equation for this reaction.
Fe2O3 + 3NaH → ……Fe + ……NaOH [2]
(ii) Explain how this equation shows that iron(III) oxide is reduced.
. …… [1]
[Total: 10]
Mark scheme
3(a)(i) boiling point of Rb: any values between 675 and 755 (°C) (inclusive of these values) (1) 2
atomic radius of K: any values between 0.195 and 0.245 (nm) (inclusive of these values) (1)
3(a)(ii) decreases (1) 1
3(a)(iii) solid (1) 2
60 °C is below the melting point / the melting point is above 60 °C (1)
3(b)(i) number of protons in the nucleus of an atom / number of positive charges in the nucleus of an atom 1
3(b)(ii) any suitable, e.g. detecting leaks in pipes / measuring thickness of paper / energy production 1
3(c)(i) 2 (Fe) (1) 2
3 (NaOH) (1)
3(c)(ii) iron(III) oxide loses oxygen / it loses oxygen 1
The structure of malic acid is shown.
H O O
C
H C O H
H C H
C
H O O
(a) (i) On the structure draw a circle around the alcohol functional group. [1]
(ii) Deduce the formula of malic acid to show the number of carbon, hydrogen and oxygen atoms.
. …… [1]
(b) When malic acid is heated it forms compound F.
The structure of compound F is shown.
H O O
C
H C
C H
C
H O O
Explain why compound F is described as unsaturated.
…… [1]
(c) Compound F can form polymers.
(i) State the meaning of the term polymer.
. ……
. …… [2]
(ii) State the name of the polymer formed when ethene is polymerised.
. …… [1]
(d) Ethanoic acid is a carboxylic acid.
Describe the observations made when dilute ethanoic acid reacts with:
magnesium ……
litmus solution. . ……
[2]
(e) The graph shows how the pH changes when dilute ethanoic acid is added slowly to aqueous sodium hydroxide.
14
12
10
pH
8
6
4
2
0 10 20 30 40 volume of dilute ethanoic acid added / cm3
(i) Deduce the pH of the aqueous sodium hydroxide before the addition of dilute ethanoic acid.
pH = …… [1]
(ii) Deduce the volume of dilute ethanoic acid added when the pH is neutral.
…… cm3 [1]
[Total: 10]
Mark scheme
4(a)(i) OH alcohol group circled 1
4(a)(ii) C4H6O5 1
4(b) it has a C=C double bond 1
4(c)(i) large molecules / long chain molecules / macromolecules (1) 2
built up from (many) small units / made from monomers (1)
4(c)(ii) poly(ethene) 1
4(d) with Mg: fizzes / bubbles / effervescence (1) 2
litmus: turns red / turns pink (1)
4(e)(i) pH 13 1
4(e)(ii) 18 (cm3) 1
(a) Calcium oxide is made by the thermal decomposition of calcium carbonate.
(i) State the meaning of the term thermal decomposition.
. ……
. …… [2]
(ii) Describe a test for calcium ions.
test . ……
observations ……
[2]
(b) Carbon dioxide is produced when dilute hydrochloric acid reacts with calcium carbonate.
CaCO3 + 2HCl → CaCl 2 + CO2 + H2O
(i) Complete the diagram to show how to measure the volume of carbon dioxide produced during this reaction.
dilute hydrochloric acid
calcium carbonate
[2]
(ii) Describe the effect of each of the following on the rate of reaction of dilute hydrochloric acid with calcium carbonate.
● The concentration of hydrochloric acid is decreased.
All other conditions stay the same.
. ……
● The temperature is increased.
All other conditions stay the same.
. ……
[2]
(c) Carbon dioxide is also formed when the hydrocarbon C3H8 is completely combusted.
(i) State the meaning of the term hydrocarbon.
. ……
. …… [2]
(ii) The hydrocarbon C3H8 is called propane.
Name the homologous series that propane belongs to.
. …… [1]
(iii) Name two substances formed by the incomplete combustion of propane.
…… and . …… [2]
[Total: 13]
Mark scheme
5(a)(i) breakdown of substance / idea of one substance forming two or more substances (1) 2
using heat / on heating (1)
5(a)(ii) add (aqueous) sodium hydroxide (1) 2
white precipitate / white solid (1)
OR
add (aqueous) ammonia (1)
no precipitate / very slight white precipitate (1)
5(b)(i) gas syringe / upturned measuring cylinder dipping into container (1) 2
apparatus is workable and airtight (1)
5(b)(ii) lower concentration of acid: decreases (in rate) / reaction slower / lower rate / slows down (1) 2
higher temperature: increases (in rate) / reaction faster / higher rate / speeds up (1)
5(c)(i) compound containing hydrogen and carbon only / compound containing hydrogen and carbon and no other substance (2) 2
if two marks not scored, 1 mark for:
compound containing hydrogen and carbon / it contains hydrogen and carbon only
5(c)(ii) alkane(s) 1
5(c)(iii) 1 mark each for any 2 of: 2
• carbon monoxide
• carbon
• water
This question is about water.
(a) The water in rivers often contains pollutants such as acids.
Describe how universal indicator paper can be used to determine the pH value of the water.
…… [2]
(b) The diagram shows some of the stages in water treatment.
impure aeration mixing purified filter water tank tank water
air chlorine
(i) Air is blown through the aeration tank.
Name the two gases that make up most of the air.
…… and . …… [2]
(ii) After aeration, the water still contains large insoluble particles.
The filter is made up of fine sand and stones.
Explain how the filter helps purify the water.
. ……
. ……
. …… [2]
(iii) Explain why chlorine is used in water treatment.
. …… [1]
(c) Anhydrous cobalt(II) chloride is used to test for water.
State the colour change in this test.
from …… to …… [2]
[Total: 9]
Mark scheme
6(a) dip indicator paper in to water (and record the colour) (1) 2
compare the colour with (universal indicator) colour chart
match colour with colour chart (1)
6(b)(i) nitrogen (1) 2
oxygen (1)
6(b)(ii) large(r) particles cannot get through (the small gaps in) the filter / large(r) particles get trapped in the filter / large(r) particles 2
too big to get through (filter) (1)
water passes through (1)
6(b)(iii) to kill bacteria / to kill micro-organisms 1
6(c) (from) blue (1) 2
(to) pink (1)
(a) Molten lead(II) bromide is electrolysed using carbon electrodes.
(i) State the products of this electrolysis at:
the negative electrode ……
the positive electrode. . ……
[2]
(ii) State the name of another substance which can be used as an inert electrode.
. …… [1]
(b) When aqueous magnesium chloride is electrolysed using carbon electrodes, hydrogen gas is produced at the negative electrode.
Complete the dot-and-cross diagram to show the electron arrangement in one molecule of hydrogen.
[1]
[Total: 4]
Mark scheme
7(a)(i) negative electrode: lead (1) 2
positive electrode: bromine (1)
7(a)(ii) platinum (1) 1
7(b) 1 shared pair of electrons AND no other electrons on either H atom (1) 1
This question is about elements in the Periodic Table.
(a) The table shows some properties of five elements, P, Q, R, S and T.
melting point density electrical conductivity atomic radius element
/ °C in g / cm3 of the solid / nm
P 1535 7.86 very good 0.125
Q –7 3.12 does not conduct 0.114
R 1495 8.90 very good 0.126
S –157 0.0035 does not conduct 0.110
T 839 1.54 very good 0.174
Use only the elements shown in the table to answer this question.
State which two of the elements, P, Q, R, S and T, are covalent molecules.
Give two reasons for your answer.
elements …… and ……
reason 1 ……
reason 2 ……
[3]
(b) Element T is on the left-hand side of the Periodic Table.
Suggest whether its oxide is acidic or basic.
Give a reason for your answer.
…… [1]
(c) Krypton is an element in Group VIII of the Periodic Table.
Explain, using ideas about electronic structure, why krypton is unreactive.
…… [1]
(d) Sodium is an element in Group I of the Periodic Table. Iron is a transition element.
Iron has a higher melting point and higher boiling point than sodium.
Give two other ways in which the properties of transition elements differ from the properties of
Group I elements.
1 ……
2 ……
[2]
(e) The table compares the reactivity of four metals with dilute hydrochloric acid.
reaction with metal dilute hydrochloric acid calcium reacts very rapidly copper no reaction iron reacts rapidly nickel reacts slowly
Put the four metals in order of their reactivity.
Put the least reactive metal first.
least reactive most reactive
[2]
(f) Hot iron reacts with steam. The reaction is reversible.
Complete the equation by writing the symbol for a reversible reaction in the box.
3Fe + 4H2O Fe3O4 + 4H2
[1]
(g) Steel is an alloy of iron.
State the meaning of the term alloy.
…… [1]
[Total: 11]
The Periodic Table of Elements
Group
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
16
rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon
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
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 – – – – – – – – – – –
The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.).
Mark scheme
8(a) Q AND S (1) 3
low melting points (1)
poor conductor (of electricity) / does not conduct (electricity) (1)
8(b) basic (oxide) AND T is a metal / metal oxides are basic 1
8(c) has a complete outer (electron) shell / has a full outer (electron) shell 1
8(d) 1 mark each for any 2 of: 2
• transition elements have a high(er) density / Group I has a low(er) density
• transition elements form coloured compounds / Group I compounds are not coloured
• transition elements form ions with different charges / Group I forms only one type of ion
• transition elements are good catalysts / Group I elements not catalysts
8(e) copper < nickel < iron < calcium (2) 2
if 2 marks not scored, 1 mark for:
1 consecutive pair reversed / calcium < iron < nickel < copper
8(f) ⇌ 1
8(g) mixture of metal with another element 1
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Chemistry 0620/31 for May/June 2021 is out of 80 marks, across 8 questions.
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