AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2023: Question 4

9 marks · Low Demand difficulty · Short Answer

Identify charge carriers, write a word equation for water dissociation, determine a chemical formula, and explain electrode reactions during the electrolysis of copper bromide solution.

Practise this question

Question

A diagram of an electrolysis cell labeled Figure 11 shows a power supply connected to a positive and negative electrode immersed in copper bromide solution. Below are seven sub-questions: 04.1 asks about charge carriers in wires; 04.2 asks for a word equation for water breakdown; 04.3 asks for the formula of copper bromide; 04.4 asks why copper ions move to the negative electrode; 04.5 asks to complete a sentence about copper production; 04.6 asks about the mass change of the negative electrode; and 04.7 asks what is produced at the positive electrode.

Question text

04 Copper bromide solution is electrolysed using inert electrodes.

Figure 11 shows the apparatus.

Figure 11

04.1 Which particles carry the electrical charge through the metal wire?

[1 mark]

Tick ( ) one box.

Electrons

Neutrons

Protons 18

There are four ions in copper bromide solution:

• Cu2+

• Br –

• H+

• OH–

04.2 Two of these ions are formed when a water molecule breaks down.

The symbol equation when a water molecule breaks down is:

H O → H+ + OH–

Complete the word equation for the breakdown of a water molecule.

[2 marks]

water → ion + ion

04.3 Copper ions and bromide ions carry the electrical charge through the solution.

The formula of a copper ion is Cu2+

The formula of a bromide ion is Br –

What is the formula of copper bromide?

[1 mark]

Tick ( ) one box.

CuBr

Cu2Br

CuBr2 19

04.4 Explain why copper ions (Cu2+) move to the negative electrode.

[2 marks]

04.5 Complete the sentence.

Choose the answer from the box.

[1 mark]

decomposed discharged distilled

At the negative electrode copper metal is produced when the

copper ions are .

04.6 What happens to the mass of the negative electrode during electrolysis?

[1 mark]

Tick ( ) one box.

Decreases

No change

Increases 20

There are four ions in copper bromide solution:

• Cu2+

• Br –

• H+

• OH–

04.7 What is produced at the positive electrode when copper bromide solution

*19* is electrolysed?

[1 mark]

Tick ( ) one box.

Bromine

Hydrogen

Oxygen

Mark scheme

Show the mark scheme

Question 4

AO /

Question Answers Extra information Mark

Spec. Ref.

04.1 electrons 1 AO1

5.2.2.8

AO /

Spec. Ref.

04.2 (water →) hydrogen (ion) + hydroxide (ion) 2 AO1

5.4.3.4

allow for 1 mark

hydrogen (ion)

allow for 1 mark

hydroxide (ion)

AO /

Spec. Ref.

04.3 CuBr2 1 AO2

5.1.1.1

5.4.2.2

AO /

Spec. Ref.

04.4 (copper ions) AO1

are positive(ly charged) 1 5.4.3.1

5.4.3.4

(so are) attracted (to the 1 RPA9

negative electrode)

AO /

Spec. Ref.

04.5 discharged 1 AO1

5.4.3.1

5.4.3.4

RPA9

AO /

Spec. Ref.

04.6 increases 1 AO2

5.4.3.1

5.4.3.4

14 RPA9

AO /

Spec. Ref.

04.7 bromine 1 AO2

5.4.3.1

5.4.3.4

RPA9

Total Question 4 9

How to answer it

Electrolysis of Copper Bromide

What this question tests

This question assesses your understanding of electrolysis in aqueous solutions. Key skills include identifying charge carriers in different materials, balancing ionic charges to write formulas, and predicting the products formed at the electrodes based on the reactivity series and ion charges.

Part 04.1

Charge Carriers in Wires

Correct Answer

Electrons

Key Knowledge

In metals (like the wire), electricity is carried by delocalised electrons.
In electrolytes (the solution), electricity is carried by ions.

Common Error

Students often confuse the wire with the solution. If the question asks about the solution, the answer is ions. If it asks about the wire, the answer is always electrons.

Part 04.2

Breakdown of Water

Correct Answer

water → hydrogen ion + hydroxide ion

1 mark for each correct ion name.

Exam Technique

The question provides the symbol equation: H₂O → H⁺ + OH⁻ . Use this! You just need to translate the symbols into words. H⁺ is hydrogen and OH⁻ is hydroxide.

Part 04.3

Chemical Formulae

Correct Answer

CuBr₂

Step-by-Step Logic

Identify the charges: Copper is 2+ and Bromide is 1- .
Compounds must be neutral (total charge = 0).
To cancel out one 2+ charge, you need two 1- charges.
Therefore, the formula is CuBr₂ .

Part 04.4

Ionic Movement

Correct Answer

Copper ions are positively charged (1 mark).
They are attracted to the negative electrode (1 mark).

The Golden Rule

In electrolysis, remember: Opposites Attract. Positive ions (cations) always move to the negative electrode (cathode).

Parts 04.5 & 04.6

At the Negative Electrode

Correct Answers

04.5: discharged

04.6: Increases

Key Knowledge

When copper ions reach the negative electrode, they gain electrons to become neutral copper atoms. This is called being discharged. Because solid copper metal is now coating the electrode, the mass of that electrode will increase.

Part 04.7

Product at the Positive Electrode

Correct Answer

Bromine

The Aqueous Rule

At the positive electrode (anode):

If halide ions (Cl⁻, Br⁻, I⁻) are present, the halogen is produced.
If no halide ions are present, oxygen is produced.
Since we have Bromide ( Br⁻ ), Bromine is the product.

Visualising the Result

If you were performing this experiment, you would see orange/brown liquid or fumes forming around the positive electrode—this is the bromine being produced!

Topics

Chemistry · C1: Atomic Structure and the Periodic Table · C2: Bonding, Structure and the Properties of Matter · C4: Chemical Changes

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.