AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2022: Question 3

13 marks · Standard Demand difficulty · Short Answer

Identify structures and bonding types for silicon dioxide, fullerenes, and polymers, and calculate percentage composition and explain hardness in alloys.

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Question

The image contains a multi-part chemistry question about structure and bonding. Figure 6 shows a giant covalent lattice of silicon dioxide with silicon and oxygen atoms labeled. Figure 7 shows a cylindrical carbon nanotube fullerene. Figure 8 depicts wavy polymer chains. Figure 9 compares the regular arrangement of atoms in pure magnesium metal to a magnesium alloy containing larger copper atoms. Questions ask for identification of structure types, bond counts, fullerene properties, polymer bonding, and a calculation of the percentage of copper atoms in the alloy shown.
Question text

03 This question is about structure and bonding.

Figure 6 represents part of the structure of silicon dioxide.

Figure 6

03.1 What type of structure is silicon dioxide?

[1 mark]

Tick ( ) one box.

Giant covalent

Ionic lattice

Simple molecular

03.2 Each oxygen atom forms two bonds.

What is the number of bonds formed by each silicon atom?

Use Figure 6.

[1 mark]

Figure 7 represents part of a fullerene.

Figure 7

03.3 Complete the sentence.

Choose the answer from the box.

[1 mark]

hexagons octagons squares triangles

The structure of fullerenes is based on .

03.4 Complete the sentence.

Choose the answer from the box.

[1 mark]

carbon hydrogen oxygen

The fullerene molecule shown in Figure 7 is made from

atoms of 11 .

03.5 What is the fullerene molecule shown in Figure 7 used for?

[1 mark]

Tick ( ) one box.

Electronics

Hand warmers

*10* Sports injury packs 12

Figure 8 represents part of the structure of a polymer.

Figure 8

03.6 What holds the atoms together in a polymer chain?

[1 mark]

Tick ( ) one box.

Covalent bonds

Ionic bonds

Metallic bonds

03.7 Complete the sentence.

Choose the answer from the box.

[1 mark]

atomic intermolecular macromolecular

In Figure 8 the polymer chains are held together by

forces.

Figure 9 represents part of the structures of:

• magnesium metal

• a magnesium alloy.

Figure 9

03.8 Calculate the percentage of copper atoms in the alloy.

[3 marks]

Number of magnesium atoms in the alloy =

Number of copper atoms in the alloy =

Total number of atoms in the alloy =

Percentage of copper atoms in the alloy = %

03.9 Explain why the magnesium alloy is harder than magnesium metal.

Use Figure 9.

[3 marks]

Mark scheme

Show the mark scheme The mark scheme table provides answers for question 3. 03.1 is 'giant covalent'. 03.2 is '4 / four'. 03.3 is 'hexagons'. 03.4 is 'carbon'. 03.5 is 'electronics'. 03.6 is 'covalent bonds'. 03.7 is 'intermolecular'. 03.8 awards 3 marks for counting 22 magnesium and 3 copper atoms, then calculating (3/25) x 100 = 12%. 03.9 awards 3 marks for explaining that different sized copper atoms distort the layers of magnesium atoms, preventing them from sliding over each other.

Question 3

AO /

Question Answers Extra information Mark

Spec. Ref.

03.1 giant covalent 1 AO1

5.2.2.6

5.2.3.1

AO /

Spec. Ref.

03.2 4 / four 1 AO3

5.2.2.6

5.2.3.1

AO /

Spec. Ref.

03.3 hexagons 1 AO1

5.2.3.3

AO /

Spec. Ref.

03.4 carbon 1 AO1

5.2.3.3

AO /

Spec. Ref.

03.5 electronics 1 AO1

5.2.3.3

AO /

Spec. Ref.

03.6 covalent bonds 1 AO1

5.2.2.5

AO /

Spec. Ref.

03.7 intermolecular 1 AO1

5.2.2.5

AO /

Spec. Ref.

03.8 (magnesium) 22 and (copper) 3 1 AO2

5.2.2.7

(percentage =)

3 allow correct use of incorrectly

(× 100) 1

25 determined value(s) for number

of magnesium atoms and / or

copper atoms

=12 (%) 1

AO /

Spec. Ref.

03.9 (alloy is harder because) 1 AO2

copper atoms are larger

or

(copper) atoms are a different

size

(so the) layers of (magnesium) 1 AO2

atoms are distorted

(and therefore the) layers allow (so) the atoms cannot 1 AO1

cannot easily slide slide over each other

5.2.1.5

5.2.2.7

Total Question 3 13

How to answer it

Structure, Bonding, and Alloys

What this question tests

This question assesses your ability to identify types of chemical structures (giant covalent, polymers, fullerenes), understand the bonding within them, and explain the physical properties of alloys using the particle model.

Part 3.1 & 3.2: Silicon Dioxide

Giant Covalent Structures

Correct Answers

  • 3.1: Giant covalent
  • 3.2: 4 (or four)

Key Knowledge

Silicon dioxide (SiO₂) has a similar structure to diamond. Every Silicon atom is covalently bonded to 4 Oxygen atoms in a massive 3D lattice.

Exam Technique

For 3.2, look closely at Figure 6. Find a "Silicon atom" (the black dot) and count how many lines (bonds) come out of it. You will see four lines connecting it to four grey dots.

Part 3.3, 3.4 & 3.5: Fullerenes

Carbon Nanotubes

Correct Answers

  • 3.3: hexagons
  • 3.4: carbon
  • 3.5: Electronics

Key Knowledge

Fullerenes are molecules of carbon atoms with hollow shapes. Carbon nanotubes are cylindrical fullerenes with high tensile strength and high electrical conductivity.

Common Error

Don't confuse fullerenes with polymers. Fullerenes are pure carbon; polymers are long chains usually containing carbon and hydrogen.

Part 3.6 & 3.7: Polymers

Bonding in Chains

Correct Answers

  • 3.6: Covalent bonds
  • 3.7: intermolecular forces

Exam Technique

Remember: Intramolecular (inside the chain) is strong covalent. Intermolecular (between the chains) is weak. The question asks what holds the atoms together (inside the chain) vs what holds the chains together.

Part 3.8: Alloy Calculation

Percentage Composition

Step-by-Step Calculation

  1. Count Magnesium atoms: Looking at Figure 9 (alloy), there are 22 light grey atoms.
  2. Count Copper atoms: There are 3 dark grey atoms.
  3. Find the Total: 22 + 3 = 25 total atoms.
  4. Calculate Percentage: (Number of Copper / Total) × 100
  5. Final Step: (3 / 25) × 100 = 12%

Calculation Trap

A common mistake is dividing by the number of Magnesium atoms (3/22) instead of the total number of atoms (3/25). Always ensure your denominator is the "whole" amount.

Part 3.9: Properties of Alloys

Why are alloys harder than pure metals?

The 3-Mark Model Answer

To get full marks, you must link the structure to the property:

  1. The copper atoms are a different size (larger) than the magnesium atoms. [1 mark]
  2. This distorts the layers of atoms. [1 mark]
  3. Therefore, the layers cannot slide over each other easily. [1 mark]

Examiner Insight

Top-level responses always mention "layers sliding." In pure metals, atoms are the same size and arranged in regular layers that slide easily, making them soft. In alloys, the different-sized atoms disrupt this regularity.

Topics

Chemistry · C2: Bonding, Structure and the Properties of Matter

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.