AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Higher), June 2025: Question 3
10 marks · Standard Demand difficulty · Short Answer
Answer questions about crude oil fractions, finite resources, calculating the volume of petrol from barrels of crude oil, petrochemical products, cracking methods, and testing for alkenes.
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Question text
03 Crude oil is a finite resource found in rocks.
03.1 What is meant by a ‘finite’ resource?
[1 mark]
03.2 Most of the compounds in crude oil are hydrocarbons.
Define the term ‘hydrocarbon’.
[1 mark]
03.3 Crude oil found in different areas has different compositions.
Table 2 shows the percentage (%) composition of crude oil from one area.
Table 2
Percentage (%)
Fraction
of fraction
Petrol 31.3
Kerosene 13.4
Diesel oil 14.4
Heavy fuel oil 40.9
The volume of crude oil is measured in a unit called ‘barrels’.
1 barrel = 159 dm3
Calculate the volume of petrol in dm3 in 90 barrels of crude oil.
Give your answer to 3 significant figures.
*10* [4 marks]
Volume of petrol (3 significant figures) = dm3
03.4 Fractions from crude oil can be processed to produce many useful materials by the
*11*petrochemical industry.
Which is a useful material produced by the petrochemical industry?
[1 mark]
Tick ( ) one box.
Alloys
Ceramics
Fertilisers
Lubricants
03.5 Catalytic cracking is used to crack hydrocarbons.
Name one other method of cracking hydrocarbons.
[1 mark]
03.6 Alkanes are produced by cracking.
Hydrocarbon Z is a different type of hydrocarbon to alkanes.
Hydrocarbon Z:
• is also produced by cracking
• can be used to produce polymers.
Describe a test for hydrocarbon Z.
Give the result of the test.
[2 marks]
Test
Result
Mark scheme
Show the mark scheme
Question 3
AO /
Question Answers Extra information Mark
Spec. Ref.
03.1 (a resource that) will run out allow (a resource that) is 1 AO1
non-renewable 5.7.1.1
5.10.1.1
AO /
Spec. Ref.
03.2 (a compound / molecule) made 1 AO1
up of carbon and hydrogen 5.7.1.1
(atoms) only – SCIENCE: TRILOGY – –
AO /
Spec. Ref.
03.3 (volume of petrol =) AO2
31.3 2 5.7.1.1
90 ×159 ×
100 5.7.1.2
or
(volume of petrol =)
31.3
14310 ×
or
(volume of petrol =)
90 × 49.767
or
(volume of petrol =)
28.17 ×159
allow 1 mark for
90 ×159
or
31.3
159 ×
or
31.3
90 ×
= 4479.03 1
= 4480 (dm3) allow an answer correctly 1
rounded to 3 significant figures
from an incorrect calculation
which uses 90 barrels, 159 dm3
– and a fraction percentage – –
AO /
Spec. Ref.
03.4 lubricants 1 AO1
5.7.1.2
AO / 13
Spec. Ref.
03.5 steam cracking 1 AO1
5.7.1.4
AO /
Spec. Ref.
03.6 (test) AO2
add bromine water 1 5.7.1.4
(result)
(bromine) changes (from allow (bromine) is decolourised 1
orange) to colourless
Total Question 3 10
How to answer it
Crude Oil, Hydrocarbons & Cracking
This question assesses fundamental recall and quantitative skills from AQA Specification 5.7 (Organic Chemistry) and 5.10 (Using Resources):
- Defining key terminology: finite resources and hydrocarbons.
- Multi-step mathematical calculation involving unit conversions, percentages, and rounding to significant figures.
- Recalling everyday products and fractions derived from the petrochemical industry.
- Identifying the two methods of industrial cracking (catalytic and steam cracking).
- Applying the chemical test for unsaturation (alkenes) using bromine water.
Question 03.1 (1 Mark)
Definition of a 'finite' resource
✅ Correct Answer
A resource that will run out (or is non-renewable / is being used up faster than it is formed).
❌ Common Errors
Writing vague statements such as "cannot be reused" or "it is bad for the environment". The examiner requires explicit reference to supply or running out.
Question 03.2 (1 Mark)
Definition of a 'hydrocarbon'
✅ Correct Answer
A compound / molecule made up of carbon and hydrogen only.
💡 Key Knowledge
The word only (or "solely") is essential. If a molecule contains oxygen, nitrogen, or chlorine, it is no longer a pure hydrocarbon.
❌ Common Errors
Writing "a mixture of carbon and hydrogen" (it is a compound, not a mixture) or forgetting the qualifying word "only".
Question 03.3 (4 Marks)
Volume of petrol in 90 barrels (to 3 significant figures)
📐 Step-by-Step Calculation
Given Data:
- 1 barrel = 159 dm³
- Number of barrels = 90
- Percentage of petrol in crude oil sample (from Table 2) = 31.3%
- Step 1: Calculate the total volume of 90 barrels of crude oil
Total volume = 90 × 159 = 14310 dm³ [1 method mark if working partially shown] - Step 2: Calculate the volume of petrol (31.3% of total)
Volume of petrol = 14310 × (31.3 ÷ 100) = 4479.03 dm³ [2 method marks for complete calculation structure + 1 unrounded value mark] - Step 3: Round to 3 significant figures
4479.03 rounds to: 4480 dm³ [1 mark for rounding]
🧠 Exam Technique: Significant Figures
Count from the first non-zero digit: 4 (1st), 4 (2nd), 7 (3rd). Look at the next digit ( 9 ). Since 9 ≥ 5, round 7 up to 8. Fill the placeholder with 0: 4480.
❌ Calculation Traps
- Leaving the answer as 4479 or 4479.03 loses the final mark.
- Selecting the wrong fraction percentage from Table 2 (e.g. kerosene at 13.4%).
Question 03.4 (1 Mark)
Products of the petrochemical industry
✅ Correct Answer
Lubricants [✓]
💡 Key Knowledge
The petrochemical industry produces fractions used as fuels (petrol, diesel, kerosene) and feedstock for useful materials: solvents, lubricants, polymers, and detergents.
Alloys (metallurgy), ceramics (clay/glass), and fertilisers (Haber process/minerals) come from different industrial sectors.
Question 03.5 (1 Mark)
Methods of cracking hydrocarbons
✅ Correct Answer
Steam cracking (or thermal cracking with steam).
💡 Key Knowledge: Two Types of Cracking
- Catalytic cracking: Hydrocarbon vapours passed over a hot zeolitic/aluminium oxide catalyst at ~550°C.
- Steam cracking: Hydrocarbon vapours mixed with steam and heated to very high temperatures (~850°C).
Question 03.6 (2 Marks)
Test and result for Hydrocarbon Z (alkenes)
💡 Identifying Hydrocarbon Z
The question states: "Hydrocarbon Z is a different type of hydrocarbon to alkanes... produced by cracking... used to produce polymers." This means Z is an alkene (containing a reactive C=C double bond).
✅ Correct Answers
Test: Add bromine water [1 mark]
Result: Turns from orange / brown to colourless (or decolourises) [1 mark]
❌ Common Errors & Misconceptions
- "Clear" is NOT colourless: A solution can be orange and clear (transparent). You must write colourless or decolourised.
- Writing "turns white" or "turns red".
- Testing with a lit splint (squeaky pop is for hydrogen, not alkenes).
Topics
Chemistry · C7: Organic Chemistry · C10: Using Resources
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Higher), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.