2025 AQA A-LEVEL CHEMISTRY Paper 3 Question Paper &
Mark Scheme (Merged) Friday 20 June 2025
[VERIFIED]Pass100%
SECTION A
1. A student performs a titration to determine the concentration of a hydrochloric acid
solution using 0.100 mol dm⁻³ sodium hydroxide. Which piece of apparatus should be used
to measure exactly 25.0 cm³ of the acid into the conical flask?
A) Burette
B) Measuring cylinder
C) 25.0 cm³ pipette
D) 25.0 cm³ beaker
Answer: C
Rationale: A volumetric pipette is designed to deliver a precise, fixed volume of liquid (25.0
cm³) with high accuracy. Burettes measure variable volumes, measuring cylinders are less
precise, and beakers are only for approximate volumes.
2. The empirical formula of a compound is CH₂O and its relative molecular mass is 180. What
is the molecular formula?
A) CH₂O
B) C₃H₆O₃
C) C₄H₈O₄
D) C₆H₁₂O₆
Answer: D
*Rationale: The empirical formula mass = 12 + (2×1) + 16 = 30. The number of empirical
units = 180 ÷ 30 = 6. Therefore molecular formula = (CH₂O)₆ = C₆H₁₂O₆.*
3. Which statement about a dative covalent bond is correct?
A) Both electrons are provided by the same atom
B) It only occurs in transition metal complexes
C) It is weaker than a normal covalent bond
D) It cannot be represented in displayed formulae
,Answer: A
Rationale: In a dative covalent (coordinate) bond, one atom provides both shared electrons.
This occurs in species like NH₄⁺, H₃O⁺, and transition metal complexes, so it is not restricted
to complexes. It can be represented with an arrow (→).
4. In the reaction: 2MnO₄⁻ + 16H⁺ + 10Cl⁻ → 2Mn²⁺ + 8H₂O + 5Cl₂, which species is reduced?
A) MnO₄⁻
B) H⁺
C) Cl⁻
D) Cl₂
Answer: A
*Rationale: In MnO₄⁻, manganese has an oxidation state of +7. In Mn²⁺, it has an oxidation
state of +2. Reduction is a decrease in oxidation number, so MnO₄⁻ is reduced.*
5. Which equation correctly represents the standard hydrogen electrode half-cell?
A) 2H⁺(aq) + 2e⁻ ⇌ H₂(g)
B) H₂(g) ⇌ 2H⁺(aq) + 2e⁻
C) H⁺(aq) + e⁻ ⇌ ½H₂(g)
D) 2H₂O(l) ⇌ O₂(g) + 4H⁺(aq) + 4e⁻
Answer: A
*Rationale: The standard hydrogen electrode (SHE) uses the reduction reaction 2H⁺(aq) +
2e⁻ → H₂(g) under standard conditions (298 K, 1 mol dm⁻³ H⁺, 1 atm H₂ pressure). The
equilibrium is written in the reduction direction.*
6. Which property is characteristic of transition metals?
A) They form colourless compounds
B) They have variable oxidation states
C) They have full d-subshells
D) They are all gases at room temperature
Answer: B
Rationale: Transition metals are defined by having partially filled d-orbitals in at least one
common oxidation state. This allows them to exhibit multiple oxidation states and form
coloured compounds. Colourless compounds and full d-subshells would not be characteristic.
, 7. A white precipitate forms when aqueous sodium hydroxide is added to a solution
containing a transition metal ion. The precipitate dissolves in excess NaOH. Which ion is
present?
A) Fe²⁺
B) Fe³⁺
C) Cu²⁺
D) Al³⁺
Answer: D
Rationale: Al³⁺ (though not a transition metal, this is a common test) forms Al(OH)₃ which is
amphoteric and dissolves in excess NaOH to form [Al(OH)₄]⁻. Fe²⁺ and Fe³⁺ form insoluble
hydroxides that do not dissolve in excess NaOH. Cu²⁺ forms a blue precipitate.
8. Which reagent would distinguish between propanal and propanone?
A) Bromine water
B) Tollens' reagent
C) 2,4-dinitrophenylhydrazine
D) Sodium carbonate solution
Answer: B
*Rationale: Tollens' reagent (ammoniacal silver nitrate) is oxidised by aldehydes to produce a
silver mirror. Ketones do not react. Both compounds react with 2,4-DNPH (orange
precipitate) and neither reacts with sodium carbonate. Bromine water reacts with alkenes,
not these carbonyls.*
9. A student heats a mixture of ethanoic acid and ethanol with concentrated sulfuric acid.
What is the main organic product?
A) Ethanal
B) Ethene
C) Ethyl ethanoate
D) Ethanoic anhydride
Answer: C
Rationale: This is esterification (condensation reaction). A carboxylic acid reacts with an
alcohol in the presence of an acid catalyst (conc. H₂SO₄) to form an ester (ethyl ethanoate)
and water. Ethanal is from oxidation of ethanol, ethene from dehydration.
10. The repeating unit of a polymer is -[CH₂-CH(C₆H₅)]ₙ-. Which monomer was used?
Mark Scheme (Merged) Friday 20 June 2025
[VERIFIED]Pass100%
SECTION A
1. A student performs a titration to determine the concentration of a hydrochloric acid
solution using 0.100 mol dm⁻³ sodium hydroxide. Which piece of apparatus should be used
to measure exactly 25.0 cm³ of the acid into the conical flask?
A) Burette
B) Measuring cylinder
C) 25.0 cm³ pipette
D) 25.0 cm³ beaker
Answer: C
Rationale: A volumetric pipette is designed to deliver a precise, fixed volume of liquid (25.0
cm³) with high accuracy. Burettes measure variable volumes, measuring cylinders are less
precise, and beakers are only for approximate volumes.
2. The empirical formula of a compound is CH₂O and its relative molecular mass is 180. What
is the molecular formula?
A) CH₂O
B) C₃H₆O₃
C) C₄H₈O₄
D) C₆H₁₂O₆
Answer: D
*Rationale: The empirical formula mass = 12 + (2×1) + 16 = 30. The number of empirical
units = 180 ÷ 30 = 6. Therefore molecular formula = (CH₂O)₆ = C₆H₁₂O₆.*
3. Which statement about a dative covalent bond is correct?
A) Both electrons are provided by the same atom
B) It only occurs in transition metal complexes
C) It is weaker than a normal covalent bond
D) It cannot be represented in displayed formulae
,Answer: A
Rationale: In a dative covalent (coordinate) bond, one atom provides both shared electrons.
This occurs in species like NH₄⁺, H₃O⁺, and transition metal complexes, so it is not restricted
to complexes. It can be represented with an arrow (→).
4. In the reaction: 2MnO₄⁻ + 16H⁺ + 10Cl⁻ → 2Mn²⁺ + 8H₂O + 5Cl₂, which species is reduced?
A) MnO₄⁻
B) H⁺
C) Cl⁻
D) Cl₂
Answer: A
*Rationale: In MnO₄⁻, manganese has an oxidation state of +7. In Mn²⁺, it has an oxidation
state of +2. Reduction is a decrease in oxidation number, so MnO₄⁻ is reduced.*
5. Which equation correctly represents the standard hydrogen electrode half-cell?
A) 2H⁺(aq) + 2e⁻ ⇌ H₂(g)
B) H₂(g) ⇌ 2H⁺(aq) + 2e⁻
C) H⁺(aq) + e⁻ ⇌ ½H₂(g)
D) 2H₂O(l) ⇌ O₂(g) + 4H⁺(aq) + 4e⁻
Answer: A
*Rationale: The standard hydrogen electrode (SHE) uses the reduction reaction 2H⁺(aq) +
2e⁻ → H₂(g) under standard conditions (298 K, 1 mol dm⁻³ H⁺, 1 atm H₂ pressure). The
equilibrium is written in the reduction direction.*
6. Which property is characteristic of transition metals?
A) They form colourless compounds
B) They have variable oxidation states
C) They have full d-subshells
D) They are all gases at room temperature
Answer: B
Rationale: Transition metals are defined by having partially filled d-orbitals in at least one
common oxidation state. This allows them to exhibit multiple oxidation states and form
coloured compounds. Colourless compounds and full d-subshells would not be characteristic.
, 7. A white precipitate forms when aqueous sodium hydroxide is added to a solution
containing a transition metal ion. The precipitate dissolves in excess NaOH. Which ion is
present?
A) Fe²⁺
B) Fe³⁺
C) Cu²⁺
D) Al³⁺
Answer: D
Rationale: Al³⁺ (though not a transition metal, this is a common test) forms Al(OH)₃ which is
amphoteric and dissolves in excess NaOH to form [Al(OH)₄]⁻. Fe²⁺ and Fe³⁺ form insoluble
hydroxides that do not dissolve in excess NaOH. Cu²⁺ forms a blue precipitate.
8. Which reagent would distinguish between propanal and propanone?
A) Bromine water
B) Tollens' reagent
C) 2,4-dinitrophenylhydrazine
D) Sodium carbonate solution
Answer: B
*Rationale: Tollens' reagent (ammoniacal silver nitrate) is oxidised by aldehydes to produce a
silver mirror. Ketones do not react. Both compounds react with 2,4-DNPH (orange
precipitate) and neither reacts with sodium carbonate. Bromine water reacts with alkenes,
not these carbonyls.*
9. A student heats a mixture of ethanoic acid and ethanol with concentrated sulfuric acid.
What is the main organic product?
A) Ethanal
B) Ethene
C) Ethyl ethanoate
D) Ethanoic anhydride
Answer: C
Rationale: This is esterification (condensation reaction). A carboxylic acid reacts with an
alcohol in the presence of an acid catalyst (conc. H₂SO₄) to form an ester (ethyl ethanoate)
and water. Ethanal is from oxidation of ethanol, ethene from dehydration.
10. The repeating unit of a polymer is -[CH₂-CH(C₆H₅)]ₙ-. Which monomer was used?
