AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2023: Question 1

10 marks · Low Demand difficulty · Short Answer

Identify properties of crude oil, its formation, separation by fractional distillation, cracking products, gas tests, and calculate percentage composition.

Practise this question

Question

A multi-part GCSE chemistry exam question about crude oil. Part 1.1 asks to identify the definition of a finite resource. Part 1.2 asks what crude oil is formed from. Part 1.3 asks what type of substance crude oil is. Part 1.4 requires completing sentences about fractional distillation using the words 'condense', 'evaporate', 'freeze', or 'melt'. Part 1.5 asks for a use of cracking products. Part 1.6 asks for the test for hydrogen gas. Part 1.7 is a calculation: '5.20 kg of crude oil contains 1.53 kg of LPG. Calculate the percentage of LPG in 5.20 kg of crude oil to 3 significant figures.'
Question text

01 Crude oil contains a large number of hydrocarbons.

01.1 Crude oil is a finite resource.

What is a finite resource?

[1 mark]

Tick ( ) one box.

A limited resource

A renewable resource

A sustainable resource

01.2 What is crude oil formed from?

[1 mark]

Tick ( ) one box.

Plankton

Volcanoes

Water 3

01.3 What type of substance is crude oil?

[1 mark]

Tick ( ) one box.

Compound

Element

Mixture

01.4 The hydrocarbons in crude oil are separated into fractions using fractional distillation.

Complete the sentences.

Choose answers from the box.

[2 marks]

condense evaporate freeze melt

In fractional distillation the crude oil is heated so

the hydrocarbons .

The fractions collect as the hydrocarbons cool and .

Hydrocarbons can be cracked to produce more useful molecules.

01.5 Complete the sentence.

Choose the answer from the box.

[1 mark]

alloys fertilisers fuels

Some products of cracking are useful as .

01.6 Hydrogen gas is a product of cracking.

What is used in the test for hydrogen gas?

[1 mark]

Tick ( ) one box.

Burning splint

Glowing splint

Limewater 5

01.7 5.20 kg of crude oil contains 1.53 kg of LPG (Liquefied Petroleum Gas).

Calculate the percentage (%) of LPG in 5.20 kg of crude oil.

Give your answer to 3 significant figures.

[3 marks]

Percentage (3 significant figures) = %

Mark scheme

Show the mark scheme The mark scheme for question 1. It provides the following answers: 1.1: a limited resource; 1.2: plankton; 1.3: mixture; 1.4: evaporate and condense; 1.5: fuels; 1.6: burning splint. For 1.7, it shows the calculation (1.53 / 5.20) x 100 = 29.42, with a final answer of 29.4% for 3 marks, noting that 3 significant figures are required.

Question 1

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 a limited resource 1 AO1

5.7.1.1

5.10.1.1

AO /

Spec. Ref.

01.2 plankton 1 AO1

5.7.1.1

AO /

Spec. Ref.

01.3 mixture 1 AO1

5.7.1.1

AO /

Spec. Ref.

01.4 evaporate 1 AO1

5.2.2.1

condense 1 5.7.1.2

AO /

Spec. Ref.

01.5 fuels 1 AO1

5.7.1.4

AO /

Spec. Ref.

01.6 burning splint – OMBINED SCIENCE: TRILOGY – 1 – AO1

5.8.2.1

AO /

Spec. Ref.

01.7 (percentage =) AO2

1.53 × 100 1 5.7.1.2

5.20

= 29.42 1 7

= 29.4 (%) allow a correctly calculated 1

answer to 3 significant figures

from an incorrect calculation

which uses values given in the

question

Total Question 1 10

How to answer it

Crude Oil: Formation, Separation, and Cracking

What this question tests

This question assesses your foundational knowledge of organic chemistry, specifically: the definition of finite resources, how crude oil is formed and classified, the physical processes of fractional distillation, the purpose of cracking, and basic chemical tests for gases.

Parts 01.1, 01.2 & 01.3

The Basics of Crude Oil

Definitions and Formation

Correct Answers

  • 01.1: A limited resource
  • 01.2: Plankton
  • 01.3: Mixture

Key Knowledge

  • Finite: It is being used up faster than it is made. It will eventually run out.
  • Formation: Crude oil is the remains of ancient biomass (mainly plankton) buried in mud under high pressure and temperature over millions of years.
  • Mixture: Crude oil contains many different hydrocarbons that are not chemically bonded together.
Part 01.4

Fractional Distillation

How we separate hydrocarbons

Correct Sentence Completion

In fractional distillation the crude oil is heated so the hydrocarbons evaporate. The fractions collect as the hydrocarbons cool and condense.

Exam Technique

Remember the order: Heating causes a liquid to turn into a gas (evaporation). Cooling causes a gas to turn back into a liquid (condensation). In a fractionating column, it is hot at the bottom and cooler at the top.

Common Errors

Students often swap these terms. You cannot "condense" by heating. Always link Heat -> Evaporate and Cool -> Condense.

Parts 01.5 & 01.6

Cracking and Chemical Tests

Making useful products

Correct Answers

  • 01.5: fuels
  • 01.6: Burning splint

Key Knowledge

  • Cracking: Breaking down long-chain hydrocarbons into smaller, more useful molecules (short-chain alkanes for fuels and alkenes for plastics).
  • Hydrogen Test: A burning splint held at the open end of a test tube creates a "squeaky pop" sound.

Common Error: The Splint Trap

Don't confuse the tests!
• Burning splint: Hydrogen (Squeaky pop)
• Glowing splint: Oxygen (Relights)
• Limewater: Carbon Dioxide (Turns cloudy)

Part 01.7

Calculation: Percentage Composition

Working with mass and significant figures

Step-by-Step Calculation

  1. Identify the values: Mass of LPG = 1.53 kg; Total mass of crude oil = 5.20 kg.
  2. Set up the equation: (Part ÷ Whole) × 100
    (1.53 / 5.20) × 100
  3. Calculate: 29.42307...
  4. Round to 3 Significant Figures: Look at the first three non-zero digits (2, 9, 4). The next digit is 2, so we round down.
    Final Answer: 29.4%

Mark Breakdown

  • 1 Mark: Correct substitution into the percentage formula.
  • 1 Mark: Correct calculation result (29.42).
  • 1 Mark: Correct rounding to 3 significant figures.

Calculation Traps

Significant Figures: This is a common place to lose the final mark. "29.42" is 4 significant figures. "29.4" is 3. Always check the requirement in the question!

Topics

Chemistry · C7: Organic Chemistry · C8: Chemical Analysis · C10: Using Resources

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.