AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2022: Question 5
11 marks · Standard Demand difficulty · Short Answer
Identify properties, names, and reactions of alkanes, perform a percentage calculation, balance a cracking equation, and evaluate life cycle assessment data for window frames.
Practise this questionQuestion
Question text
05 This question is about hydrocarbons.
Figure 9 shows a hydrocarbon.
Figure 9
05.1 Complete the formula for the hydrocarbon shown in Figure 9.
[1 mark]
C H
05.2 What is the name of the hydrocarbon in Figure 9?
[1 mark]
05.3 Which homologous series does the hydrocarbon in Figure 9 belong to?
[1 mark]
05.4 30 g of another hydrocarbon contains 24 g of carbon.
Which calculation gives the percentage of carbon in the hydrocarbon?
[1 mark]
Tick ( ) one box.
24 × 30
100 × 30
24 × 100
30 × 100
05.5 Table 3 shows boiling points of some hydrocarbons.
Table 3
Formula of hydrocarbon Boiling point in °C
C2H6 –89
C4H10 0
C6H14 69
C8H18 125
C10H22 174
Describe how the boiling points change as the number of carbon atoms in the
hydrocarbon increases.
[1 mark]
Hydrocarbons can be cracked.
05.6 Give one condition used to crack hydrocarbons.
*19* [1 mark]
05.7 Balance the equation for the cracking of C6H14
[1 mark]
C6H14 → C2H6 + C2H4
05.8 Give one reason why hydrocarbons are cracked.
[1 mark]
05.9 Window frames can be manufactured from wood or plastic.
Table 4 shows the results of a life cycle assessment (LCA) for making one wooden
and one plastic window frame.
Both window frames are the same size.
Table 4
Wooden frame Plastic frame
Total energy used in MJ 9150 9713
Coal and oil used in kg 5 18
Waste produced in kg 16 28
Cost to buy and maintain in £ 147 102
Give three advantages of using wood instead of plastic in the manufacture of
window frames.
[3 marks]
Advantage of wood 1
Advantage of wood 2
Advantage of wood 3
Mark scheme
Show the mark scheme
Question 5
AO /
Question Answers Extra information Mark
Spec. Ref.
05.1 C3H8 1 AO2
5.7.1.1
AO /
Spec. Ref.
05.2 propane 1 AO1
5.7.1.1
AO /
Spec. Ref.
05.3 alkane(s) 1 AO1
5.7.1.1
AO /
Spec. Ref.
05.4 24 × 100 1 AO2
30 5.7.1.1
AO /
Spec. Ref.
05.5 (as the number of carbon atoms 1 AO2
increases the) boiling point 5.7.1.3
increases
AO /
16Question Answers Extra information Mark
Spec. Ref.
05.6 any one from: 1 AO1
• high temperature allow a temperature between 5.7.1.4
400 °C and 900 °C
ignore heat / hot
• steam
• high pressure
• low / no oxygen (atmosphere)
• catalyst allow aluminium oxide
allow alumina
allow zeolites
allow porous pot
AO /
Spec. Ref.
05.7 C6H14 → C2H6 + 2C2H4 allow multiples 1 AO2
5.1.1.1
5.3.1.1
5.7.1.4
AO /
Spec. Ref.
05.8 any one from: 1 AO1
• to make smaller molecules 5.7.1.4
• to make more useful
molecules
• to produce fuels
• more demand for smaller
molecules
• to make (starting materials allow to make (starting materials
for) polymers for) other chemicals
allow to make alkenes
AO /
Spec. Ref.
05.9 any three from: 3 AO3 17
(wood) 5.10.2.1
• uses less energy
• uses less coal / oil
• produces less waste
• is renewable / sustainable
Total Question 5 11
How to answer it
Hydrocarbons, Cracking, and LCAs
What this question tests
This question assesses your ability to identify and name alkanes, interpret trends in physical properties (boiling points), understand the conditions and purpose of catalytic cracking, balance chemical equations, and evaluate environmental impacts using Life Cycle Assessment (LCA) data.
Alkane Basics
💡 Key Knowledge
- Alkanes are saturated hydrocarbons (only single bonds).
- General formula: CₙH₂ₙ₊₂
- Naming Mnemonic: Monkeys Eat Peeled Bananas (Meth-, Eth-, Prop-, But-).
✅ Correct Answers
- 05.1: C₃H₈
- 05.2: Propane
- 05.3: Alkane(s)
🧠 Exam Technique
In 05.1, simply count the atoms in Figure 9. There are 3 Carbon (C) atoms and 8 Hydrogen (H) atoms. Don't overthink it! For the name, remember that 3 carbons = "Prop-".
Percentages & Trends
📐 Calculation (05.4)
To find the percentage of carbon:
- Identify the mass of carbon: 24 g
- Identify the total mass: 30 g
- Formula: (Part ÷ Total) × 100
- Calculation: (24 ÷ 30) × 100
❌ Common Errors
Students often flip the fraction (30/24) or multiply by 100 at the wrong stage. Always check: is your answer less than 100%? If you used 30/24, you'd get 125%, which is impossible!
✅ Correct Answer (05.5)
As the number of carbon atoms increases, the boiling point increases.
Examiner Tip: Always look for the pattern in the table. -89 to 0 to 69... the numbers are getting larger (less negative/more positive).
Cracking Hydrocarbons
💡 Cracking Conditions
Cracking requires breaking strong covalent bonds. You need:
- High temperature (400°C - 900°C)
- A catalyst (e.g., zeolite or aluminium oxide) OR Steam
✅ Balancing the Equation (05.7)
C₆H₁₄ → C₂H₆ + 2 C₂H₄
How to solve: Count carbons on the left (6). On the right, you have 2 in C₂H₆. You need 4 more. Since each molecule of the second product has 2 carbons, you need 2 of them (2 × 2 = 4).
🧠 Why Crack? (05.8)
Short-chain molecules are in higher demand as fuels (they ignite easier). Cracking also produces alkenes, which are used to make plastics (polymers).
Life Cycle Assessment (LCA)
💡 Evaluating Wood vs Plastic
When comparing materials, look at energy use, raw materials, and end-of-life. Wood is generally seen as more sustainable because:
- It is renewable (trees can be replanted).
- It often uses less energy to process than crude oil.
- It acts as a carbon sink while the tree is growing.
- It produces less waste or the waste is biodegradable.
🧠 How to get 3/3 Marks
Even if the table isn't visible, LCA questions usually want you to compare specific categories. For wood, focus on: Renewability, Lower Energy usage, and Lower Fossil Fuel (coal/oil) usage.
Topics
Chemistry · C7: Organic Chemistry · C10: Using Resources · C3: Quantitative Chemistry
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.