AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2022: Question 4

13 marks · Standard Demand difficulty · Short Answer

Analyze properties, reactions, and extraction of metals and compounds including balancing equations, relative formula mass calculations, and bonding explanations for conductivity.

Practise this question

Question

A chemistry exam paper featuring seven sub-questions about magnesium and sodium. It includes a chemical equation to balance (Mg + O2 -> MgO), a calculation for relative formula mass of MgF2, an explanation of argon's lack of reactivity, a reactivity series diagram for matching metals D and E to extraction methods, and two structural diagrams: one of an ionic lattice for sodium chloride and one of a metallic lattice for sodium metal, each with a prompt to explain electrical conductivity.
Question text

04 This question is about elements and compounds.

04.1 Magnesium and oxygen react to produce magnesium oxide.

Balance the equation for the reaction.

[1 mark]

Mg + O2 → 2MgO

04.2 Suggest one safety precaution that should be taken when heating magnesium

and oxygen.

[1 mark]

04.3 Calculate the relative formula mass (Mr) of magnesium fluoride (MgF2).

Relative atomic masses (Ar): F = 19 Mg = 24

[2 marks]

Relative formula mass (Mr) =

04.4 Argon is a noble gas.

Explain why no product is formed when magnesium and argon are heated together.

[2 marks]

04.5 Figure 10 shows a reactivity series.

Figure 10

Most reactive

Metal D

Sodium

Magnesium

Carbon

Metal E

Iron

Hydrogen

Copper

Least reactive

Draw one line from each metal to the method used to extract that metal.

Use Figure 10.

[2 marks]

Metal Method used to extract that metal

Extracted by electrolysis of a

molten ionic compound.

Metal D Extracted from its oxide by

reduction with carbon.

Extracted from its oxide by

reduction with hydrogen.

*16* Metal E

Removed from the Earth as the

18 metal itself.

A substance conducts electricity when it has charged particles that are free to move.

04.6 Figure 11 represents the structure of sodium chloride.

Figure 11

Explain why sodium chloride conducts electricity when molten but not when solid.

*17* [3 marks]

04.7 Figure 12 represents the structure of sodium metal.

Figure 12

Explain why sodium metal conducts electricity when solid.

[2 marks]

Mark scheme

Show the mark scheme The mark scheme for question 4, totaling 13 marks. It lists correct answers: '2' for balancing the magnesium equation; safety goggles or avoiding direct light for precautions; 62 for the relative formula mass of MgF2; full outer shell for argon's lack of reactivity; Metal D linked to electrolysis and Metal E to carbon reduction; ions free to move in molten NaCl but fixed in solid; and delocalised electrons carrying charge in sodium metal.

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 2 Mg + O2 → 2 MgO allow multiples 1 AO2

5.1.2.5

5.4.1.1

AO /

Spec. Ref.

04.2 any one from: 1 AO3

• wear safety glasses / 5.4.1.1

goggles 5.4.1.2

• do not look directly at allow look through blue 5.5.1.1

burning magnesium glass

• wear heat proof glove

allow use tongs

allow tie hair back

AO /

Spec. Ref.

04.3 (Mr = ) 24 + (2 × 19) 1 AO2

5.1.2.5

= 62 1 5.3.1.2

AO /

Spec. Ref.

04.4 any one from: allow energy level for shell 1 AO2

• argon has a full outer shell

• argon has 8 electrons in the

outer shell

• argon has a stable

arrangement of electrons.

allow does not need to lose

and / or gain electrons

(so) argon is unreactive ignore argon is a noble gas 1 AO1

5.1.2.4 15

AO /

Spec. Ref.

04.5 AO3

5.4.1.2

5.4.1.3

5.4.3.1

5.4.3.2

5.4.3.3

do not accept more than one line from a box on the left

AO /

Spec. Ref.

04.6 (because) ions 1 AO1

5.2.2.3

(which are) free to move 1

when molten

(but are) fixed in solid 1

allow reference to charged

particles for MP2 and MP3

AO /

Spec. Ref.

04.7 (sodium contains) delocalised allow free electrons 1 AO1

electrons 5.2.2.8

(which) carry (electrical) charge ignore throughout for through 1

(through the metal / sodium)

ignore current / electricity

Total Question 4 13

How to answer it

Elements, Compounds, and Reactivity

What this question tests

This question assesses your ability to balance chemical equations, calculate relative formula mass, and explain chemical properties using atomic structure. It also covers the reactivity series, metal extraction methods, and the reasons why different substances conduct electricity.

Part 04.1

Balancing Equations

Correct Answer

2 Mg + O₂ → 2 MgO

1 Mark: For the correct coefficient '2' in front of Mg.

Exam Technique

Count the atoms on the right first. There are 2 Magnesiums and 2 Oxygens in 2 MgO . On the left, you already have O₂ , so you just need to double the Mg .

Part 04.2

Safety Precautions

Accepted Answers

  • Wear safety goggles/glasses.
  • Do not look directly at the burning magnesium.
  • Wear heat-proof gloves.
  • Use tongs to handle the magnesium.

Examiner Insight

Vague answers like "be careful" or "wear a lab coat" usually don't score. Think about the specific hazard: burning magnesium produces a very bright light (UV) and high heat.

Part 04.3

Calculating Relative Formula Mass (Mᵣ)

Step-by-Step Calculation for MgF₂

  1. Identify the atoms: 1 x Magnesium (Mg) and 2 x Fluorine (F).
  2. Look up Aᵣ values: Mg = 24, F = 19.
  3. Multiply by the number of atoms: 24 + (2 × 19)
  4. Final Sum: 24 + 38 = 62

Final Answer: 62

Common Trap

Students often forget to multiply the Fluorine by 2. The subscript ₂ only applies to the element immediately before it.

Part 04.4

Noble Gas Reactivity

Key Knowledge

Argon is in Group 0. It has a full outer shell (8 electrons). This makes it stable, so it does not need to lose or gain electrons.

How to get 2 Marks

1. State that argon has a full outer shell (or 8 electrons in the outer shell). [1 Mark]

2. Conclude that it is therefore unreactive / stable. [1 Mark]

Part 04.5

The Reactivity Series & Extraction

Extraction Rules

  • Above Carbon: Extracted by electrolysis (too reactive for carbon to reduce).
  • Below Carbon: Extracted by reduction with carbon.
  • Below Hydrogen: Can be reduced by hydrogen (though carbon is cheaper).
  • Very Low Reactivity: Found as pure metal (e.g., Gold).

Correct Matching

Metal D → Extracted by electrolysis of a molten ionic compound.

Metal E → Extracted from its oxide by reduction with carbon.

Part 04.6

Conductivity in Ionic Compounds

The 3-Mark Answer

Sodium chloride contains ions. [1 Mark]

In a solid, these ions are fixed in a lattice and cannot move. [1 Mark]

When molten, the ions are free to move and carry the charge. [1 Mark]

The "Electron" Error

Never say "electrons move" in an ionic compound. This is the most common way students lose marks. In ionic chemistry, it is always the ions that move.

Part 04.7

Conductivity in Metals

Diagram Description

If asked to draw this, you should show a regular grid of positive metal ions surrounded by a "sea" of small dots representing delocalised electrons.

Key Facts

  • Metals have delocalised electrons.
  • These electrons are free to move through the whole structure.
  • They carry the electrical charge.

Mark Scheme Requirements

1. Mention delocalised electrons (or free electrons). [1 Mark]

2. State that they carry the charge through the metal. [1 Mark]

Topics

Chemistry · C1: Atomic Structure and the Periodic Table · C2: Bonding, Structure and the Properties of Matter · C3: Quantitative Chemistry · C4: Chemical Changes

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.