AQA GCSE Chemistry Chemistry Paper 1 (Foundation), June 2024: Question 6
10 marks · Low Demand difficulty · Short Answer
Answer questions on the electrolysis of molten substances, balancing the extraction equation for aluminium, calculating the relative formula mass of aluminium oxide, and metal extraction methods using the reactivity series.
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Question text
06 This question is about electrolysis and the extraction of metals.
06.1 Why can some molten substances be electrolysed?
[1 mark]
Tick ( ) one box.
Electrons can move through the molten substance to the electrodes.
Ions can move through the molten substance to the electrodes.
Protons can move through the molten substance to the electrodes.
06.2 Table 3 shows the products of the electrolysis of some molten compounds.
Complete Table 3.
[3 marks]
Table 3
Product at negative Product at positive
Molten compound
electrode electrode
Lead chloride Chlorine
Potassium iodide Potassium
Zinc Bromine
Aluminium is extracted by electrolysing molten aluminium oxide.
06.3 Balance the equation for the reaction.
Choose numbers from the box.
[2 marks]
23 4 5
*28* 2Al2O3 → Al + O2
06.4 Calculate the relative formula mass (Mr) of aluminium oxide (Al2O3).
Relative atomic masses (Ar): O = 16 Al = 27
[2 marks]
30 Relative formula mass (M ) =
r
06.5 Figure 13 shows part of the reactivity series of metals.
The non-metal carbon has been included.
Figure 13
Metals can be extracted from their compounds by:
• electrolysis
• reduction with carbon.
Electrolysis is more expensive than reduction with carbon.
*29* Predict one metal that would be extracted by each method.
Use Figure 13.
[2 marks]
Extracted by electrolysis
Extracted by carbon reduction
Mark scheme
Show the mark scheme
Question 6
AO /
Question Answers Extra information Mark
Spec. Ref.
06.1 ions can move through the 1 AO1
molten substance to the 4.4.3.1
electrodes
AO /
Question Answers Mark
Spec. Ref.
06.2 Product at Product at AO2
Molten compound negative positive 4.4.3.2
electrode electrode
Lead chloride Lead Chlorine 1
Potassium iodide Potassium Iodine 1
Zinc bromide Zinc Bromine 1
AO /
Spec. Ref.
06.3 2Al2O3 → 4Al + 3O2 2 AO2
4.1.1.1
allow 1 mark for 4 Al 4.4.3.3
allow 1 mark for 3 O2
AO /
Spec. Ref.
06.4 (Mr =) AO2
(27 × 2) + (16 × 3) 1 4.3.1.2
= 102 – – 1 –
AO /
Spec. Ref.
06.5 (by electrolysis) AO3
any one from: 1 4.4.1.2
• potassium / K 4.4.1.3
• lithium / Li 4.4.3.3
allow aluminium / Al
allow sodium / Na
allow calcium / Ca
allow magnesium / Mg
(by carbon reduction)
any one from: 1
• zinc / Zn
• tin / Sn
allow iron / Fe
allow copper / Cu
Total Question 6 10
How to answer it
Electrolysis & Metal Extraction Study Guide
What this question tests
- Electrical conductivity in molten compounds: Understanding why ionic substances conduct when molten (free-moving ions, not electrons).
- Electrolysis of molten binary salts: Predicting products formed at the cathode (negative electrode) and anode (positive electrode).
- Balancing chemical equations: Conserving atoms in the extraction of aluminium (2Al₂O₃ → 4Al + 3O₂).
- Relative formula mass (Mr): Calculating Mr from relative atomic masses (Ar).
- Reactivity series & methods of extraction: Using position relative to carbon to select electrolysis vs reduction with carbon.
Why Molten Substances Can Be Electrolysed
Tick (✓) one box
✅ Correct Answer
[✓] Ions can move through the molten substance to the electrodes.
💡 Key Knowledge
- Solid ionic compounds have ions held in fixed positions within a giant ionic lattice—they can only vibrate, so they cannot conduct.
- When melted (molten) or dissolved in water, the electrostatic bonds break and ions become free to move and carry charge.
❌ Common Errors
- "Electrons can move...": A very frequent mistake! Delocalised electrons carry charge in metals and graphite, but in ionic compounds, moving ions carry charge.
- "Protons can move...": Protons are locked inside the atomic nuclei and never move during electrolysis or electrical conduction.
🧠 Exam Technique
Always pause and identify the type of substance. For ionic compounds undergoing electrolysis, the answer must mention ions moving.
Products of Molten Electrolysis
Complete Table 3
✅ Completed Table
| Molten compound | Product at negative electrode (cathode) | Product at positive electrode (anode) |
|---|---|---|
| Lead chloride | Lead [1 mark] | Chlorine |
| Potassium iodide | Potassium | Iodine [1 mark] |
| Zinc bromide [1 mark] | Zinc | Bromine |
💡 Rules for Molten Binary Compounds
- Negative electrode (cathode): Attracts positive metal ions (cations) → forms the metal element.
- Positive electrode (anode): Attracts negative non-metal ions (anions) → forms the non-metal element.
- Naming compounds: Metal name stays the same; non-metal ending changes from -ine to -ide (e.g. Zinc + Bromine → Zinc bromide).
❌ Common Errors
- Writing "iodide" instead of iodine for the element produced at the electrode.
- Writing "zinc bromine" instead of zinc bromide for the compound.
- Mixing up which ion goes to which electrode: Remember PANIC (Positive Anode, Negative Is Cathode) and opposite charges attract!
Balancing the Aluminium Extraction Equation
2Al₂O₃ → __ Al + __ O₂ (Choose from: 2, 3, 4, 5)
✅ Correct Balanced Equation
2Al₂O₃ → 4 Al + 3 O₂
📐 Step-by-Step Atom Count
- Count atoms on the left (reactants):
• Aluminium: 2 × Al₂ = 4 Al atoms
• Oxygen: 2 × O₃ = 6 O atoms - Balance aluminium on the right:
• Need 4 Al atoms → place a 4 in front of Al. - Balance oxygen on the right:
• Need 6 O atoms. Since oxygen exists as diatomic O₂ molecules: 6 ÷ 2 = 3.
• Place a 3 in front of O₂.
🧠 Exam Technique
- Marks are awarded independently: 1 mark for 4 Al and 1 mark for 3 O₂.
- Never change the small subscript numbers (like Al₂ or O₃); only add large balancing numbers in front of the chemical formulas.
- Double-check that total atoms on left equal total atoms on right.
Calculating Relative Formula Mass (Mr)
Calculate the Mr of aluminium oxide (Al₂O₃). Given: Ar of O = 16, Al = 27
📐 Step-by-Step Calculation
- Break down formula into constituent elements:
Formula has 2 aluminium atoms and 3 oxygen atoms. - Multiply each Ar by number of atoms:
Al: 2 × 27 = 54
O: 3 × 16 = 48
(27 × 2) + (16 × 3) [1 mark] - Sum the totals:
54 + 48 = 102 [1 mark]
Relative formula mass (Mr) = 102
❌ Common Errors
- Multiplying the whole mass: Doing (27 + 16) × 5 — make sure you match the subscript to the specific element!
- Using atomic numbers instead of mass numbers: Using Al = 13 and O = 8 instead of the provided Ar values.
- Adding units: Relative formula mass (Mr) has no units (do not write grams).
Extraction Methods from Reactivity Series
Use Figure 13 to predict one metal extracted by each method
✅ Accepted Answers
- Extracted by electrolysis: Potassium OR Lithium [1 mark]
(Mark scheme also allows: aluminium / Al, sodium / Na, calcium / Ca, magnesium / Mg) - Extracted by carbon reduction: Zinc OR Tin [1 mark]
(Mark scheme also allows: iron / Fe, copper / Cu)
💡 The Extraction Rule
- Above Carbon: Metals are more reactive than carbon. Carbon cannot displace them, so they must be extracted using electrolysis (an expensive method requiring huge electrical energy).
- Below Carbon: Metals are less reactive than carbon. Carbon can displace them from their oxides via reduction (heating with carbon/coke), which is much cheaper.
- Unreactive metals (e.g. Gold): Found native (as pure uncombined elements) in the Earth's crust.
🧠 Exam Technique: "Use Figure 13"
When the question says "Use Figure 13", the safest approach is to choose metals directly listed in that diagram!
- Metals shown above carbon in Figure 13: Potassium, Lithium.
- Metals shown below carbon in Figure 13: Zinc, Tin.
❌ Common Errors
- Naming Carbon as the metal extracted (carbon is a non-metal).
- Naming Gold for carbon reduction (gold is native; it does not need reduction from an ore).
- Giving both metals from the same section (e.g. putting zinc for electrolysis).
Topics
Chemistry · C1: Atomic Structure and the Periodic Table · C3: Quantitative Chemistry · C4: Chemical Changes
Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Foundation), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.