AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2021: Question 1

11 marks · Low Demand difficulty · Short Answer

This question tests knowledge of reversible reactions, properties of substances, and water treatment processes including filtration, sterilisation, and the classification of substances.

Practise this question

Question

The image contains a series of chemistry questions labeled 01 through 01.8. It includes a word equation for the reaction between water and anhydrous copper sulfate, a diagram of a sealed container, a matching exercise for substances and their descriptions, and multiple-choice questions regarding water treatment processes.
Question text

01 Fresh water contains low levels of dissolved salts.

Water reacts with anhydrous copper sulfate in a reversible reaction.

The word equation for the reaction is:

water + anhydrous copper sulfate ⇌ hydrated copper sulfate

01.1 How does the equation show that the reaction is reversible?

[1 mark]

01.2 Complete the sentences.

Choose answers from the box.

[2 marks]

blue green orange white yellow

The colour of anhydrous copper sulfate is .

The colour of hydrated copper sulfate is .

01.3 Figure 1 shows anhydrous copper sulfate in a sealed container.

Figure 1

*02* Suggest one reason why anhydrous copper sulfate is kept in a sealed container.

[1 mark]

Sodium chloride dissolves in water to form sodium chloride solution.

01.4 Draw one line from each substance to the description of the substance.

[2 marks]

Substance Description of substance

Compound

Sodium chloride solution

Element

Hydrocarbon

Water

Mixture

01.5 Name the process used to obtain solid sodium chloride from

sodium chloride solution.

[1 mark]

01.6 Two processes used to obtain potable water from fresh water are:

• filtering

• sterilising.

Give one reason why each process is used.

[2 marks]

Filtering

Sterilising

01.7 Which type of water is the easiest to obtain potable water from?

[1 mark]

Tick ( ) one box.

Ground water

Salt water

Waste water

01.8 Which of the following is the first stage of waste water treatment?

[1 mark]

Tick ( ) one box.

Aerobic biological treatment of effluent

Anaerobic digestion of sewage sludge

Screening and removal of grit

Mark scheme

Show the mark scheme The image is a table showing the mark scheme for questions 01.1 through 01.8. It lists the correct answers, provides extra guidance for marking, indicates the number of marks for each part, and references the Assessment Objectives and specification points.

AO /

Question Answers Extra information Mark

Spec. Ref.

01.1 (the symbol) ⇌ allow description of reversible 1 AO1

sign 5.6.2.1

must be in this order

01.2 white 1 AO1

5.6.2.2

blue 1

01.3 to prevent reaction with water allow to prevent reaction with 1 AO3

vapour (in the air) moisture 5.6.2.2

allow to keep water out

01.4 AO2

5.1.1.2

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

01.5 evaporation 1 AO1

or RPA 13

crystallisation

01.6 (filtering) to remove solids 1 AO1

5.10.1.2

(sterilising) to kill bacteria allow to kill microbes 1

01.7 ground water 1 AO1

5.10.1.3

01.8 screening and removal of grit 1 AO1

5.10.1.3

Total 11

How to answer it

Water Analysis and Purification

What this question tests

This question assesses your understanding of reversible reactions, the chemical test for water using copper sulfate, and the industrial processes used to make potable water (safe drinking water) from fresh and waste sources.

Parts 01.1 & 01.2

Reversible Reactions & Water Tests

💡 Key Knowledge

  • The symbol ⇌ means the reaction can go both forwards and backwards.
  • Anhydrous means "without water".
  • Hydrated means "with water".

✅ Correct Answers

  • 01.1: The symbol ⇌ (or "the double arrow").
  • 01.2: Anhydrous = white; Hydrated = blue.

🧠 Exam Technique

In 01.2, the order is vital. If you swap the colours, you will lose both marks. Remember: Blue = Bath (water). If water is present, it turns blue!

Part 01.3

Storage of Chemicals

💡 Why use a sealed container?

Anhydrous copper sulfate is used to test for water. If left open, it will react with water vapour (moisture) in the air and turn blue before you even use it in an experiment.

✅ Correct Answer

To prevent it reacting with water vapour / moisture in the air.

[1 mark]
Parts 01.4 & 01.5

Substances & Separation

🧠 Matching Substances

Sodium chloride solution: Because it is salt dissolved in water, it is a mixture (the two substances aren't chemically bonded).

Water (H₂O): This is a compound because hydrogen and oxygen are chemically joined in a fixed ratio.

❌ Common Errors

Don't confuse "Mixture" with "Compound". If you see the word "solution", it is almost always a mixture.

✅ Correct Answers

01.4: Sodium chloride solution → Mixture | Water → Compound.

01.5: Evaporation or Crystallisation (to get the solid salt back from the liquid solution).

Part 01.6

Making Potable Water

💡 The Two-Step Process

Fresh water (from rivers/lakes) isn't safe yet. We need to do two distinct things:

  1. Filtering: Physical removal of "bits" (sand, grit, leaves).
  2. Sterilising: Biological removal of "life" (bacteria, viruses, microbes) using Chlorine, Ozone, or UV light.

✅ Correct Answer

  • Filtering: To remove solids / insoluble particles.
  • Sterilising: To kill bacteria / microbes.
[2 marks]
Parts 01.7 & 01.8

Water Sources & Waste Treatment

💡 Water Sources

Ground water (from aquifers) is the easiest to treat because it has already been filtered by rocks and has low levels of salt compared to sea water.

🧠 Waste Water Stages

The very first thing that happens to sewage is screening. This is where large objects (like wet wipes or grit) are caught in metal bars/grids.

✅ Correct Answers

01.7: Ground water.

01.8: Screening and removal of grit.

Topics

Chemistry · C6: The Rate and Extent of Chemical Change · C8: Chemical Analysis · C10: Using Resources

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.