Chemistry Past Paper Questions

AS Paper 2, June 2023 - Outline two ways that waste hydrocarbon polymers can be processed usefully, rather than being disposed of in landfill sites. [2 marks]
- Recycled (to make other plastic materials)
- Combustion to generate energy / electricity
- As (organic) feedstock
AS Paper 2, June 2023 - [Context: Radical Substitution]. The yield of CH₃CH₂CHBrCH₃ is only 30%. Suggest two reasons why the yield of CH₃CH₂CHBrCH₃ is so low. [2 marks]
- Further substitution
- Substitution in a different position
AS Paper 2, June 2023 - The student mixes butan-2-ol, sodium bromide and sulfuric acid in a pear-shaped flask, and refluxes the mixture.
After 1 hour, the mixture in the flask has separated into two layers: an aqueous layer and an organic layer.
Describe the procedures the student would need to carry out to obtain a pure, dry sample of 2-bromobutane from this mixture.
- Separating funnel (to separate organic and aqueous layers)
- Dry organic layer with anhydrous salt/drying agent (e.g.: CaCl₂)
- Distil and collect fraction at [boiling point of 2-bromobutane]
This question is about the oxidation of two alcohols that are structural isomers of C₃H₈O.
Compare the oxidation of these two structural isomers using different reaction conditions.
For each reaction include:
• the reaction conditions
• the functional group of any organic product
• a balanced equation.
In your equations, use [O] to represent the oxidising agent and show any organic compounds as structures.
- CH₃CH₂CH₂OH AND CH₃CHOHCH₃
- Distillation for aldehyde AND reflux for carboxylic acid OR ketone
- CH₃CH₂CH₂OH → aldehyde OR → carboxylic acid
- CH₃CHOHCH₃ → ketone
- CH₃CH₂CH₂OH + [O] → CH₃CH₂CHO + H₂O
  OR CH₃CHOHCH₃ + [O] → CH₃COCH₃ + H₂O
  OR CH₃CH₂CH₂OH + 2[O] → CH₃CH₂

Describe, with the aid of suitable diagrams showing orbital overlap, the difference in bonding between structure A and structure B [4 marks]
- p-orbitals overlap (to form pi / π-bonds)
- π-bond(s) are delocalised in structure B
- π-bonds are localised / between two carbons in structure A
June 2017 A-Level Paper 1: The reactivity of Group 2 elements Mg-Ba decreases down the group. Explain why. [3 marks]
- Increasing size: Atomic radius increases OR more shells OR more (electron) shielding
- Attraction: Nuclear attraction decreases OR (outer) electron(s) experience less
- Ionisation energy: Ionisation energy decreases OR less energy needed to remove electron(s)
June 2017 A-level Paper 2: The C=C group in an alkene contains a π-bond. Complete the diagram below to show how p-orbitals are involved in the formation of a π-bond. [1 mark]
June 2017 A-level Paper 2: Describe a method to obtain a pure sample of [3-nitrobenzoic acid] from the impure solid and check its purify. [4? marks - I removed the calculation bit]
- Purification
  - Recrystallisation
  - Dissolve impure solid in minimum volume of hot water/solvent
  - Cool solution and filter solid
  - Wash with cold water/solvent and dry
- Checking purity
  - Obtain melting point
  - Compare to known values
  - Pure sample will have a (sharp) melting point very close to data book value
June 2017 A-level Paper 2:
Apply your knowledge of the bonding in arenes to explain the trend in the relative ease of nitration. [3 marks]
- Arenes = benzene
- phenol: a (lone) pair of electrons on O is (partially) delocalised/donated into the $\pi$ -system / ring
- benzoic acid: the –COOH group on benzoic acid is an electron withdrawing group
- Links electron density in $\pi$ -bond to reactivity
  - In phenol electron density is higher AND The ring is more susceptible to attack
  - In benzoic acid electron density is lower AND The ring is less susceptible to attack

June 2017 - A-level Paper 3: The H–O–H bond angle in ice is about 109° but about 105° in gaseous H₂O. Explain why there is this difference. [3 marks]
- Ice has hydrogen bonds/bonding
- H₂O_(g) 2 bonded pairs AND 2 lone pairs
- Lone pairs repel more (than bonded pairs)
June 2017 - A-level Paper 3:The rate constant, k, for this reaction is determined at different temperatures, T. Explain how the student could determine the activation energy, Ea, for the reaction graphically using values of k and T. [3 marks]
- Plot graph using ln k AND 1/T
- (Measure) gradient
- E_a = (–)R _^x gradient OR (–)8.314 _^x gradient
June 2018 - A-level Paper 1: Explain what is meant by the term enthalpy change of hydration. [2 marks]
- (enthalpy change when)
- 1 mole of gaseous ions react OR 1 mole of hydrated/aqueous ions are formed
- gaseous ions dissolve in water OR gaseous ions form aqueous/hydrated ions
June 2018 - A-level Paper 1: Predict how the enthalpy changes of hydration of F– and Cl – would differ. Explain your answer. [2 marks]
- Correct comparison of ∆_hyd linked to sizes: ∆_hydH (F^–) more negative/exothermic (than ∆_hydH (Cl^–)) AND F – has smaller size (than Cl^– )
- Comparison of attraction between ions and water F^– OR smaller sized ion linked to greater attraction to H₂O
June 2018 - A-level Paper 1: Explain what is meant by the term average bond enthalpy. [2 marks]
- Breaking of one mole of bonds
- In gaseous molecules
June 2018 - A-level Paper 1: The halogens show trends in their properties down the group. The boiling points of three halogens are shown below.

Explain why the halogens show this trend in boiling points. [3 marks]
- London forces increase OR induced dipole(–dipole) interactions increase
- (Number of) electrons increases
- More energy to break intermolecular forces OR to break London forces OR to break induced dipole(–dipole) interactions
June 2018 - A-level Paper 1: Describe and explain how the student should determine the end point of this titration accurately. (Na₂O₃^2--I₂) [2 marks]
- Add starch (near the end point)
- Blue to colourless
June 2018 - A-level Paper 2: A solid organic compound can be purified by recrystallisation. Which statement(s) about recrystallisation is/are true? [1 mark - MCQ]
1 The organic compound is more soluble in hot solvent.
2 The hot solution is cooled before the purified organic compound is collected.
3 The melting point of the purified organic compound is lower than the impure compound.
- Answer: only 1 and 2
June 2018 - A-level Paper 2: Explain why phenol is nitrated more readily than benzene. [3 marks]
- (In phenol) a (lone) pair of electrons on O is(partially) delocalised/donated into the $\pi$ system / ring
- Electron density increases/is higher (than benzene)
- (phenol) is more susceptible to electrophilic attack OR (phenol) attracts/accepts electrophile/HNO₃ more OR (phenol) polarises electrophile/HNO₃ more
June 2018 - A-level Paper 2: The rate of hydrolysis of a haloalkane depends on the halogen present. State and explain how the halogen in the haloalkane affects the rate of hydrolysis. [2 marks]
- C–F bond is hydrolysed slowest OR C–I bond is hydrolysed faster than C–Br OR C–Br has shorter reaction time than C–Cl
- C–I bond is the weakest OR C–I has lower bond enthalpy than C–Br OR C–Br is broken more easily/readily than C–Cl OR C–Hal bond strength decreases down group (7)
June 2018 - A-level Paper 2: Describe a chemical test to confirm that cinnamaldehyde and methylcinnamaldehyde contain a carbonyl group. How could the products of this test be used to distinguish between the two compounds? Your answer should not include spectroscopy. [3 marks]
- (Add) 2,4-dinitrophenylhydrazine AND orange/yellow/red precipitate
- Take melting point (of crystals)
- Compare to known values/database
June 2018 - A-level Paper 2:

Explain the difference in the boiling points of the fuels. [4 marks]
- heptane (has a longer chain so) has more points of contact / more surface interaction (between molecules)
- heptane has stronger/more induced dipole(–dipole) interactions
- pentan-1-ol has hydrogen bonds that are strong(er than induced dipole–dipole interactions) OR (alcohols have) hydrogen bonds and induced dipole(-dipole) interactions/London forces
- More energy is required to break induced dipole(–dipole) interactions in heptane than hexane OR More energy is required to break hydrogen bonds
June 2018 - A-level Paper 3:

Explain the properties shown in Table 1.1 in terms of bonding and structure. [5 marks]
- NaCl OR MgCl₂ - 2 marks
  - Giant ionic OR ionic lattice
  - Ions are mobile in liquid state
- SiCl₄ OR PCl₃ OR SCl₂ - 2 marks
  - (Simple) molecular OR simple covalent (lattice)
  - Induced dipole(–dipole) forces/interactions OR London forces
- Comparison of bond strengths - 1 mark
- Ionic bonds are stronger than London forces OR Ionic bonds need more energy to break than London forces

June 2018 - A-level Paper 3: Give details of the purification of solid paracetamol. [part of a 6 marker] - extra detail in bold
- Dissolve impure solid in minimum volume of hot solvent
- Cool solution and filter solid
- Scratch with glass rod
- Wash with cold solvent/solvent and dry

Red blood cells contain haemoglobin.
Explain using ligand substitutions:
• how haemoglobin transports oxygen around the body
• why carbon monoxide is toxic. [3 marks]
- O₂ (coordinately or datively) bonds with Fe²⁺/Fe(II)/Fe/Iron
- (When required) O₂ is replaced by H₂O OR CO₂ OR O₂ is replaced by CO OR H₂O OR CO₂ is replaced by O₂
- CO forms strong(er) bonds (than O₂)
June 2019 - A-level Paper 1: The first ionisation energy of sodium is more endothermic than that of potassium. Explain why. [2 marks]
- Sodium has a smaller atomic radius/fewer shells
- nuclear attraction increases/outer electrons experience more attraction
June 2019 - A-level Paper 1: The lattice enthalpy of sodium oxide is more exothermic than that of potassium oxide. Explain why. [2 marks]
- ionic radius of sodium / Na+ is smaller
- Na+ has stronger attraction to O^2-
June 2019 - A-level Paper 2: Describe, in terms of orbital overlap, the similarities and differences between the bonding in the Kekule model and the delocalised model of benzene. [3 marks]
- Similarities
  - Orbital overlap (sideways) overlap of p orbitals
  - π bond π bond/system/ring above and below (bonding (C) atoms/ring/plane)
- Difference
  - Kekule has: alternating π bonds OR 3 π bonds / localised (π electrons) / overlap in one direction / 2 electrons in π bond
    AND Delocalised has: π ring (system) / all p orbitals overlap OR (π electrons) spread around ring / overlap in both directions / 6 electrons in π bond
June 2019 - A-level Paper 2: Describe two pieces of evidence to support the delocalised model of benzene. [2 marks] - 2 of 3:
- Bond length (C–C)
  - bond length is between single (C–C) and double bond (C=C) OR all (C–C) bond lengths are the same
- ΔH hydrogenation
  - ∆H hydrogenation less (exothermic) than expected
- Resistance to reaction
  - Benzene is less reactive than alkenes
  - OR bromination of benzene requires a catalyst/halogen carrier
  - OR benzene does not react with/decolourise bromine (at room temperature)
  - OR benzene reacts by substitution
  - OR benzene does not (readily) react by addition
June 2019 - A-level Paper 3: Describe how the student can recrystallise the impure crystals to obtain pure (solid). [2 marks]
- Dissolve in the minimum quantity of hot water/
- Cool AND Filter AND (leave to) dry

June 2019 - A-level Paper 3: Suggest two modifications that the student could make to their method to be confident that all the oxygen had been removed (from lead oxide). Explain your reasoning. [2 marks]
- Heat to constant mass (Ensures all lead oxide has reacted)
- Spread/stir/break up lead oxide OR increase surface area OR use powder rather than lumps (Ensures all lead oxide has reacted)
- Pass methane/inert gas/N2 through tube as it cools OR don’t pass cold air (Prevents O2 reacting with Pb)
- Use excess methane OR more methane (Ensures all lead oxide has reacted)
- Bubble (escaping) gas through lime water (Ensures all lead oxide has reacted OR ensures all CO2 has been produced)

June 2024 - A-level Paper 1:
- Al (Giant metallic)
  - Giant metallic structure/lattice
  - Strong metallic bonding
  - Electrostatic attraction between (positive) metal ions/cations and delocalised electrons
  - A lot of energy needed to break bonds
- Si (Giant covalent)
  - Each Si atom forms 4 bonds / bonds with 4 other Si atoms
  - Giant covalent structure/lattice
  - Strong covalent bonds between atoms
  - Between shared pair of electrons and adjacent nuclei
  - Most energy needed to break bonds
- P, S (Simple covalent)
  - Simple covalent / molecular structure/lattice
  - Strong covalent bonds between atoms
  - Weak induced dipole–dipole interactions between molecules/London forces
  - Least energy to overcome the forces
  - Melting point of S8 > P4
  - More electrons
  - Stronger induced dipole–dipole interactions

June 2024 - A-level Paper 2: Describe two limitations of the synthesis of 2-bromo-2-methylpropane from an alkane and bromine. [2 marks]
- Further substitution/s
  OR Different termination products
  OR More than one termination step
- Substitution at different positions along (carbon) chain
June 2024 - A-level Paper 3: Describe how the student would prepare 100.0 cm3 of this solution, giving quantities, apparatus and method. [3 marks out of original 5 marker with calculation part]
- Dissolve solid in (distilled) water (less than 100 cm3 ) (in beaker)
- Transfer (solution) to volumetric flask
  AND Wash/rinse (from beaker to flask)
- Make up to mark/up to 100 cm3 with (distilled water)
  AND Invert flask (several times to ensure mixing)

June 2024 - A-level Paper 3:

June 2024 - A-level Paper 3: