O Level Chemistry 5070 Paper 21, May/June 2026

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5070/21 · May/June 2026

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Choose from the following compounds to answer the questions. ${A l C l}_{3}$ ${C H}_{4}$ $C_{2} H_{4}$ ${C O}_{2}$ $K B r$ ${N H}_{2} O H$ $N O$ ${N a}_{2} O$ ${S O}_{2}$ $Z n O$ Each compound can be used once, more than once or not at all. State which compound:

is amphoteric

[1]

has a molecule with only three atoms

[1]

has a molecule with only 18 electrons

[1]

has an element with an oxidation number of +2

[1]

is unsaturated.

[1]

Sodium azide, ${N a N}_{3}$ , decomposes when heated to make sodium and nitrogen. $2 {N a N}_{3} (s) \to 2 N a (s) + 3 N_{2} (g)$

A sample of $13.6 g$ of sodium azide is fully decomposed. Calculate the volume of nitrogen, measured at r.t.p., that is formed. Give your answer to three significant figures. volume of nitrogen = .................................................. ${d m}^{3}$

[3]

b(i)

Sodium azide has a giant ionic lattice. Explain what is meant by the term giant ionic lattice.

[1]

b(ii)

Predict two physical properties of sodium azide. 1 ........................................................................................................................................ 2 ........................................................................................................................................

[2]

b(iii)

Deduce the formula of an azide ion.

[1]

Describe the separation, arrangement and motion of the molecules in nitrogen gas.

[3]

Draw a dot-and-cross diagram to show the electronic configuration in a molecule of nitrogen. Show only the outer shell electrons.

[1]

Explain why nitrogen has a very low boiling point.

[1]

Hydrogen reacts with oxygen to make water. $2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (g)$ Figure 3.1 shows the reaction pathway diagram for this reaction.

a(i)

The reaction is exothermic. Explain how the reaction pathway diagram shows that the reaction is exothermic.

[1]

a(ii)

Explain why the reaction is exothermic. Use ideas about bond breaking and bond making.

[2]

Explain what is meant by the term activation energy, $E_{a}$ , used in Figure 3.1.

[1]

The equation for the overall chemical reaction that takes place within a hydrogen–oxygen fuel cell is shown. $2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (l)$ Describe one advantage and one disadvantage of using a hydrogen–oxygen fuel cell to power a motor vehicle rather than using a gasoline engine. advantage ................................................................................................................................. ................................................................................................................................................... disadvantage ............................................................................................................................ ...................................................................................................................................................

[2]

The rate of reaction between hydrogen gas and oxygen gas decreases when the pressure is decreased at constant temperature. Explain why.

[2]

The rate of reaction between hydrogen gas and oxygen gas decreases when the temperature is decreased at constant pressure. Explain why.

[2]

Potassium iodide is an ionic compound.

Concentrated and dilute aqueous potassium iodide are separately electrolysed using graphite electrodes. Complete Table 4.1 about the products of the two electrolysis reactions. Table 4.1

[4]

Molten potassium iodide is electrolysed using graphite electrodes. Construct ionic half-equations to show the reactions at the anode and at the cathode. anode ........................................................................................................................................ cathode .....................................................................................................................................

[2]

State two reasons why graphite is a suitable material for the electrodes used in electrolysis. 1 ................................................................................................................................................ 2 ................................................................................................................................................

[2]

d(i)

The ionic equation for the reaction between aqueous potassium iodide and aqueous copper(II) chloride is shown. $4 I^{-} + 2 {C u}^{2 +} \to 2 C u I + I_{2}$ State the oxidation number of copper in copper(II) chloride.

[1]

d(ii)

The reaction is an example of a redox reaction. Explain how the equation shows that both oxidation and reduction take place during the reaction. oxidation ............................................................................................................................ ........................................................................................................................................... reduction ........................................................................................................................... ...........................................................................................................................................

[2]

Aluminium sulfate is prepared by reacting excess aluminium with hot dilute sulfuric acid. $2 A l (s) + 3 H_{2} {S O}_{4} (a q) \to {A l}_{2} ({S O}_{4})_{3} (a q) + 3 H_{2} (g)$

Use the equation to predict one observation made during this reaction.

[1]

Explain why an excess of aluminium is used in this preparation.

[1]

A sample of $3.24 g$ of aluminium is added to $50.0 {c m}^{3}$ of $2.50 m o l / {d m}^{3}$ sulfuric acid. Show by calculation that the aluminium is in excess.

[3]

Describe how excess aluminium is removed from the reaction mixture.

[1]

Describe how pure dry aluminium sulfate crystals are prepared from aqueous aluminium sulfate.

[3]

The formula of aluminium sulfate crystals is ${A l}_{2} ({S O}_{4})_{3} \cdot 16 H_{2} O$ . Calculate the percentage by mass of water of crystallisation in these crystals. percentage by mass = ..............................

[3]

Describe the effect of adding aqueous sodium hydroxide drop by drop until in excess to a sample of aqueous aluminium sulfate.

[2]

Iron is a transition element. Iron has good electrical conductivity.

State two chemical properties that are typical of a transition element. 1 ................................................................................................................................................ 2 ................................................................................................................................................

[2]

Explain why iron has good electrical conductivity. Use ideas about structure and bonding.

[1]

c(i)

Iron is used to make stainless steel. Name two elements that are mixed with iron to make stainless steel. 1 ........................................................................................................................................ 2 ........................................................................................................................................

[2]

c(ii)

Stainless steel is used to make cutlery because it is hard. Explain why stainless steel is harder than pure iron. Use ideas about structure and bonding.

[2]

c(iii)

Describe the extraction of iron from hematite in the blast furnace. You may include word equations in your answer.

[5]

Proteins are natural condensation polymers. Figure 7.1 shows a section of a protein.

Define the term condensation in the phrase condensation polymerisation.

[1]

b(i)

Name the type of monomer used to make proteins.

[1]

b(ii)

Draw the general structure of the monomer used to make proteins.

[1]

b(iii)

Proteins contain the amide linkage. Circle an amide linkage on Figure 7.1.

[1]

c(i)

Nylon is a synthetic polyamide. Name the two types of monomer that are used to make nylon. ............................................................... and ..............................................................

[2]

c(ii)

Describe one environmental challenge caused by the disposal of plastics such as nylon.

[1]

This question is about alcohols.

Describe the manufacture of ethanol from ethene. Include a symbol equation and the conditions for the manufacture.

[3]

Draw the displayed formula of butan-2-ol.

[1]

c(i)

Ethanol reacts with propanoic acid to form an ester. State the name of this ester.

[1]

c(ii)

Draw the structural formula of this ester.

[1]

c(iii)

State one condition needed for this esterification reaction.

[1]

Deduce the molecular formula of an unbranched alcohol that has only eight carbon atoms in its molecule and only one alcohol functional group.

[2]

Mark scheme

5070/21 · May/June 2026

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1a · 1 mark

1 mark
ZnO

1b · 1 mark

1 mark
CO2 / SO2

1c · 1 mark

1 mark
NH2OH

1d · 1 mark

1 mark
ZnO / NO

1e · 1 mark

1 mark
C2H4

2a · 3 marks

1 mark
moles of NaN3 = 13.6 / 65 OR 0.20923
1 mark
mols of N2 = 1.5 × 13.6 / 65 OR 1.5  0.20923 OR 0.313846
1 mark
vol of N2 = 7.53 (dm3)

2b(i) · 1 mark

1 mark
regular arrangement of (alternating) positive and negative ions

2b(ii) · 2 marks

1 mark
high melting point / high boiling point
1 mark
conducts electricity in (aqueous) solution

2b(iii) · 1 mark

1 mark
N3–

2c · 3 marks

1 mark
(separation) particles are widely apart / large distance between particles / spread far apart / are far apart
1 mark
(arrangement) random arrangement / irregular arrangement
1 mark
(motion) moving (very) fast / have a large amount of kinetic energy / random (motion)

2d · 1 mark

1 mark
Triple bond shared between two N atoms and one non-bonded pair on each N atom

2e · 1 mark

1 mark
weak intermolecular forces

3a(i) · 1 mark

1 mark
energy of products less than energy of reactants

3a(ii) · 2 marks

1 mark
bond breaking endothermic AND bond making exothermic / energy absorbed to break bonds AND energy released on making bonds
1 mark
more energy released than absorbed

3b · 1 mark

1 mark
minimum energy that colliding particles must have in order to react

3c · 2 marks

1 mark
advantage: water is the only product / no carbon dioxide made / higher efficiency / quieter / transfer more energy per gram of fuel / (hydrogen is) a renewable (source of energy)
1 mark
disadvantage: idea of difficult to store the hydrogen (under pressure) / limited availability of hydrogen

3d · 2 marks

1 mark
particles are less crowded / distance between particles is greater / fewer particles per unit volume
1 mark
fewer collisions per second / lower collision frequency

3e · 2 marks

1 mark
particles move slower / particles have less kinetic energy
1 mark
less successful collisions / fewer collisions with equal or more than activation energy / fewer particles with equal or more than activation energy / less effective collisions / less energetic collisions

4a · 4 marks

1 mark
concentrated aqueous potassium iodide, product formed at anode: iodine / I2
1 mark
dilute aqueous potassium iodide, product formed at anode: oxygen (and water) / O2 (and H2O)
1 mark
concentrated aqueous potassium iodide, product formed at cathode: hydrogen / H2
1 mark
dilute aqueous potassium iodide, product formed at cathode: hydrogen / H2

4b · 2 marks

1 mark
(anode) 2I– → I2 + 2e–
1 mark
(cathode) K+ + e– → K

4c · 2 marks

1 mark
inert / does not react with electrolyte or products
1 mark
good electrical conductivity

4d(i) · 1 mark

1 mark
+2

4d(ii) · 2 marks

1 mark
(oxidation) iodide(ion) loses electrons / oxidation number of iodine increases
1 mark
(reduction) copper(II) ions gain electrons / oxidation number of copper decreases

5a · 1 mark

1 mark
bubbles / fizzes / effervesces / colourless solution obtained

5b · 1 mark

1 mark
to use up all the acid

5c · 3 marks

1 mark
mol of aluminium = 0.12 OR 3.24 / 27 (OR mol of H2SO4 = 0.050  2.50 OR 0.125)
1 mark
so mols of H2SO4 needed = 0.12  1.5 OR 0.18 (OR so mol of aluminium needed 0.0125 ÷ 1.5 OR 0.0833)
1 mark
actual mol of H2SO4 = 0.050  2.50 OR 0.125 (so not enough H2SO4) (OR actual mol of aluminium = 0.12 (so excess aluminium) OR mass aluminium needed is 2.25 g (so is in excess))

5d · 1 mark

1 mark
filtration

5e · 3 marks

M1
heat solution to get a saturated solution / heat to reduce volume by half / heat to reach crystallisation point / heat to the first appearance of crystals
M2
allow (solution) to evaporate slowly / leave (solution) to cool
M3
filter off crystals, wash with water and dry with filter paper

5f · 3 marks

1 mark
Mr of Al2(SO4)3 = 342 or formula mass of 16H2O = 288
1 mark
Mr of hydrated salt = 630 OR (%)100  288/630
1 mark
= 46 / 45.7

5g · 2 marks

1 mark
white precipitate
1 mark
soluble in excess resulting in colourless solution

6a · 2 marks

1 mark
act as catalysts
1 mark
more than one oxidation state (in compounds)
1 mark
form coloured compounds

6b · 1 mark

1 mark
has mobile electrons

6c(i) · 2 marks

1 mark
carbon
1 mark
nickel
1 mark
chromium

6c(ii) · 2 marks

1 mark
stainless steel has particles with different sizes
1 mark
layers (of atoms or ions) in steel cannot slide as easily as in pure iron

6c(iii) · 5 marks

1 mark
coke burns/reacts with oxygen/air to make carbon dioxide / carbon + oxygen → carbon dioxide / C + O2 → CO2
1 mark
coke reacts with carbon dioxide to make carbon monoxide / carbon + carbon dioxide → carbon monoxide / C + CO2 → 2CO
1 mark
carbon monoxide reacts with iron(III) oxide to make iron / carbon monoxide + iron(III) oxide → carbon dioxide + iron / Fe2O3 + 3CO → 3CO2 + 2Fe
1 mark
calcium carbonate forms (carbon dioxide and) calcium oxide / calcium carbonate → carbon dioxide + calcium oxide / CaCO3 → CaO + CO2
1 mark
calcium oxide reacts with sand to make slag / calcium oxide + silicon dioxide → calcium silicate / CaO + SiO2→ CaSiO3

7a · 1 mark

1 mark
forms compound and a small molecule / where two molecules react with loss of a small molecule

7b(i) · 1 mark

1 mark
amino acid

7b(ii) · 1 mark

1 mark
Correct displayed or structural formula of the amino acid monomer

7b(iii) · 1 mark

1 mark
any one circle around an amide / peptide group

7c(i) · 2 marks

1 mark
diamine
1 mark
dicarboxylic acid

7c(ii) · 1 mark

1 mark
land-fills (may fill up) / accumulation of plastics/nylon in oceans / formation of toxic gases during burning

8a · 3 marks

1 mark
C2H4 + H2O → CH3CH2OH
1 mark
300 °C
1 mark
60 atm / 6000 kPa
1 mark
acid catalyst

8b · 1 mark

1 mark
Displayed formula of butan-2-ol

8c(i) · 1 mark

1 mark
ethyl propanoate

8c(ii) · 1 mark

1 mark
CH3CH2COOCH2CH3

8c(iii) · 1 mark

1 mark
heat / reflux / acid catalyst

8d · 2 marks

2 marks
C8H18O

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O Level Chemistry 5070 Paper 21, May/June 2026

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Question paper

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1a · 1 mark

1b · 1 mark

1c · 1 mark

1d · 1 mark

1e · 1 mark

2a · 3 marks

2b(i) · 1 mark

2b(ii) · 2 marks

2b(iii) · 1 mark

2c · 3 marks

2d · 1 mark

2e · 1 mark

3a(i) · 1 mark

3a(ii) · 2 marks

3b · 1 mark

3c · 2 marks

3d · 2 marks

3e · 2 marks

4a · 4 marks

4b · 2 marks

4c · 2 marks

4d(i) · 1 mark

4d(ii) · 2 marks

5a · 1 mark

5b · 1 mark

5c · 3 marks

5d · 1 mark

5e · 3 marks

5f · 3 marks

5g · 2 marks

6a · 2 marks

6b · 1 mark

6c(i) · 2 marks

6c(ii) · 2 marks

6c(iii) · 5 marks

7a · 1 mark

7b(i) · 1 mark

7b(ii) · 1 mark

7b(iii) · 1 mark

7c(i) · 2 marks

7c(ii) · 1 mark

8a · 3 marks

8b · 1 mark

8c(i) · 1 mark

8c(ii) · 1 mark

8c(iii) · 1 mark

8d · 2 marks

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