AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2020: Question 6

9 marks · Standard Demand difficulty · Short Answer

Answer questions about the extraction of aluminium, including atomic structure, reduction, electrode wear in electrolysis, and charge carriers in graphite, molten electrolyte, and metal wire.

Practise this question

Question

A GCSE chemistry question titled "This question is about the extraction of aluminium" with four parts. Part 06.1 shows the nuclide symbol for aluminium, 27 over 13 Al, and asks for the number of electrons and neutrons in the aluminium atom, with two answer lines and 2 marks. Part 06.2 says aluminium is produced by reduction of aluminium oxide, Al2O3, and asks what is meant by reduction, worth 1 mark. Part 06.3 states that oxygen is formed at the positive carbon electrodes in an electrolysis cell and asks why the positive carbon electrodes must be continually replaced, worth 3 marks. A labelled diagram of the electrolysis cell shows a container of molten mixture of aluminium oxide and cryolite, carbon electrodes, a negative electrode, positive electrodes connected by metal wire, and molten aluminium at the bottom. Part 06.4 asks for the free-moving charged particles in a carbon electrode made from graphite, in the molten mixture of aluminium oxide and cryolite, and in a metal wire, with three bullet points and 3 marks.
Question text

06 This question is about the extraction of aluminium.

06.1 An aluminium atom is represented as:

13Al

Give the number of electrons and neutrons in the aluminium atom.

[2 marks]

Number of electrons

Number of neutrons

Aluminium is extracted by the electrolysis of a molten mixture of aluminium oxide

and cryolite.

Figure 11 shows the cell used for the electrolysis.

Figure 11

06.2 Aluminium is produced by the reduction of aluminium oxide (Al2O3).

What is meant by the term reduction?

[1 mark]

06.3 Oxygen is formed at the positive carbon electrodes.

Explain why the positive carbon electrodes must be continually replaced.

*20* [3 marks]

06.4 A substance conducts electricity because of free moving, charged particles.

What are the free moving, charged particles in a:

• carbon electrode (made from graphite)

• molten mixture of aluminium oxide and cryolite

• metal wire?

[3 marks]

Carbon electrode (made from graphite)

Molten mixture of aluminium oxide and cryolite

Metal wire

Mark scheme

Show the mark scheme The mark scheme lists answers for four subparts. For 06.1, the number of electrons is 13 and the number of neutrons is 14, in that order only, each worth 1 mark. For 06.2, the correct idea is loss of oxygen; it also allows aluminium ions gaining electrons or aluminium oxide losing oxygen, worth 1 mark. For 06.3, the positive carbon electrode is allowed to be called the anode; at high temperature oxygen reacts with the carbon electrode, so the positive electrode burns or wears away to produce carbon dioxide, with separate marking points worth 3 marks total and the equation C + O2 → CO2 credited for relevant points. For 06.4, the accepted charge carriers are delocalised electrons in graphite, ions in the molten mixture, and delocalised electrons in the metal wire, each worth 1 mark.

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 13 this order only 1 AO2

5.1.1.4

14 1 5.1.1.5

06.2 loss of oxygen allow (Al3+) gain of electrons 1 AO1

5.4.1.1

allow aluminium oxide loses 5.4.1.3

oxygen

06.3 allow anode for (positive)

electrode

(at high temperature) 1 AO1

oxygen reacts with carbon / 5.4.3.1

electrode 5.4.3.2

5.4.3.3

(so the positive) electrode 1

burns / wears away

to produce carbon dioxide 1

C + O2 → CO2 scores MP1 and

MP3

06.4 (delocalised) electron(s) 1 AO1

ion(s) 1 AO2

(delocalised) electron(s) 1 AO1

5.2.2.3

5.2.2.8

5.2.3.2

Total 9

How to answer it

Extraction of Aluminium

What this question tests:

This question assesses your understanding of atomic structure, the chemical definition of reduction, the industrial process of electrolysis, and the nature of charge carriers in different materials.

Part (a): Atomic Structure

Correct Answer

Number of electrons: 13

Number of neutrons: 14

Key Knowledge

For an atom 2713Al:

  • The bottom number (atomic number) is the number of protons. In a neutral atom, protons = electrons.
  • The top number (mass number) is protons + neutrons.
  • Calculation: 27 - 13 = 14 neutrons.

Part (b): Defining Reduction

Correct Answer

Reduction is the loss of oxygen (or gain of electrons).

Exam Technique

Remember the acronym OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). However, in the context of metal extraction, "loss of oxygen" is the most direct definition.

Part (c): The Positive Electrode

Correct Answer

The oxygen produced at the positive electrode reacts with the carbon (graphite) to form carbon dioxide (CO₂). This causes the electrode to burn away/wear away, requiring it to be replaced.

Common Errors

Students often forget to mention that the electrode is made of carbon. You must link the oxygen produced to the reaction with the carbon electrode.

Part (d): Charge Carriers

Correct Answer

  • Carbon electrode: Delocalised electrons
  • Molten mixture: Ions
  • Metal wire: Delocalised electrons

Key Knowledge

Conductivity depends on the presence of charged particles that are free to move:

  • Metals/Graphite: Use delocalised electrons.
  • Ionic compounds (molten/dissolved): Use ions (cations and anions).

Topics

Chemistry · C1: Atomic Structure and the Periodic Table · C4: Chemical Changes · C2: Bonding, Structure and the Properties of Matter

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.