AQA GCSE Chemistry Chemistry Paper 1 (Higher), 2024: Question 6

11 marks · Standard Demand difficulty · Extended Answer

Analyze the reactivity of metals based on cell voltage data, plan an experiment to investigate the effect of electrolyte concentration on voltage, and describe the operation of a hydrogen fuel cell.

Practise this question

Question

The image shows a chemistry exam question about chemical cells. It includes a diagram of a cell with a nickel electrode and another metal electrode in a sodium chloride solution connected to a voltmeter, a table of results showing voltages for different metals, and three sub-questions (06.1, 06.2, 06.3) requiring students to order metals by reactivity, plan an experiment, and describe a hydrogen fuel cell.
Question text

06 A student investigated the voltage produced by different pairs of metal electrodes in a

chemical cell.

Figure 6 shows the apparatus.

Figure 6

This is the method used.

1. Place a nickel electrode and an electrode made from a different metal (electrode A)

in 1.0 mol/dm3 sodium chloride solution.

2. Measure the voltage produced.

3. Repeat using different metals for electrode A.

Table 3 shows the results.

Table 3

Electrode A Symbol of metal Voltage in volts

Copper Cu –0.59

Magnesium Mg 2.12

Nickel Ni 0.00

Silver Ag –1.05

Zinc Zn19 0.51

06.1 Write the symbols of the five metals in Table 3 in order of reactivity.

Justify your answer.

[3 marks]

Most reactive Least reactive

Justification

06.2 The voltage produced by a chemical cell depends on the concentration of the

electrolyte solution.

Plan an experiment to investigate how the voltage produced by a chemical cell varies

with the concentration of the electrolyte solution.

The following substances are available:

• the metal electrodes in Table 3

• 1.0 mol/dm3 sodium chloride solution

• pure water.

[6 marks]

06.3 Describe how a hydrogen fuel cell produces a potential difference.

[2 marks]

Mark scheme

Show the mark scheme The mark scheme provides the answers for question 6. It lists the correct order of metal reactivity (Mg, Zn, Ni, Cu, Ag) with justification, outlines the marking criteria for the 6-mark experimental planning question, and provides the points for describing how a hydrogen fuel cell works (hydrogen is oxidised to produce water).

Question 6

AO /

Question Answers Extra information Mark

Spec. Ref.

allow name of metal for symbol

06.1 (most reactive) AO3

Mg Zn Ni Cu Ag 2 4.4.1.2

(least reactive) allow 1 mark for 4.5.2.1

(most reactive)

Mg Zn Ni

or

Ni Cu Ag

(least reactive)

(justification)

the higher the (positive) voltage allow the most reactive (metal) 1

the more reactive the metal has the highest (positive)

voltage

allow the least reactive (metal)

has the most negative voltage

allow the greater the difference

in reactivity the greater the

(magnitude of the) voltage– – –

AO /

Question Answers Mark

Spec. Ref.

06.2 Level 3: The method would lead to the production of a valid 5–6 AO3

outcome. The key steps are identified and logically sequenced. 4.3.4

4.5.2.1

Level 2: The method would not necessarily lead to a valid 3–4

outcome. Most steps are identified, but the method is not fully

logically sequenced.

Level 1: The method would not lead to a valid outcome. Some 1–2

relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative content

• set up cell with sodium chloride solution as the electrolyte

• use two different metals as electrodes

• measure voltage

• repeat at different concentrations of electrolyte solution

• by diluting the sodium chloride solution with water

• using measured volumes of sodium chloride solution and water

• measure volumes with a measuring cylinder (allow pipette /

burette)

• use the same two metals each time

• use the same volume of electrolyte solution

AO /

Spec. Ref.

06.3 ignore references to electrodes AO1

4.5.2.2

hydrogen is oxidised allow hydrogen loses electrons 1

(electrochemically)

to produce water 1

Total Question 6 11

How to answer it

Investigating Chemical Cells and Reactivity

What this question tests

This question assesses your understanding of electrochemical cells. You need to be able to:

  • Interpret voltage data to determine the reactivity series of metals.
  • Plan a valid scientific investigation, identifying independent, dependent, and control variables.
  • Explain the chemical process inside a hydrogen fuel cell (oxidation and products).
Part 06.1

Ordering Metals by Reactivity

Using voltage data to rank metals

Correct Answer

Order: Mg, Zn, Ni, Cu, Ag

Justification: The higher the (positive) voltage, the more reactive the metal.

3 Marks: 2 for correct order, 1 for justification.

Key Knowledge

  • A chemical cell produces a voltage based on the difference in reactivity between two metals.
  • In this experiment, Nickel is the reference (0.00V).
  • Metals with a positive voltage are more reactive than Nickel.
  • Metals with a negative voltage are less reactive than Nickel.

🧠 Exam Technique: Reading the Table

Look at the numbers like a number line. Magnesium (+2.12) is the furthest "up" the reactivity scale, while Silver (-1.05) is the furthest "down". Even if you aren't sure about the signs, remember that the magnitude (size) of the voltage tells you how far apart they are from Nickel.

Part 06.2

Experimental Design (6 Marks)

Investigating Concentration vs. Voltage

🧠 How to get 6 Marks (Level 3)

To reach the top marks, your method must be logical and complete. You must explain how to change the concentration and what to keep the same.

📐 Step-by-Step Method

  1. Set up the cell: Place two different metals (e.g., Magnesium and Copper) into a beaker.
  2. Initial Concentration: Fill the beaker with a set volume (e.g., 50 cm³) of 1.0 mol/dm³ sodium chloride solution.
  3. Measure: Record the voltage shown on the voltmeter.
  4. Dilute: Create different concentrations by mixing the 1.0 mol/dm³ solution with pure water (e.g., 80% solution, 60% solution). Use a measuring cylinder for accuracy.
  5. Repeat: Measure the voltage for each new concentration.
  6. Control: Ensure the same two metals and the same total volume of liquid are used every time.

❌ Common Errors

  • Changing the metals: The question asks how concentration affects voltage. If you change the metals, you've changed two things at once!
  • Vague volumes: Don't just say "add water." Say "measure a specific volume using a measuring cylinder."

💡 Variables

  • Independent: Concentration of electrolyte.
  • Dependent: Voltage produced.
  • Control: Type of metals, volume of solution, temperature.
Part 06.3

Hydrogen Fuel Cells

The chemistry of clean energy

Correct Answer

  • Hydrogen is oxidised (it loses electrons).
  • This produces water (H₂O).
2 Marks: 1 for oxidation, 1 for water.

💡 Key Knowledge

In a fuel cell, the overall reaction is:

2H₂ + O₂ → 2H₂O

Hydrogen enters at the negative electrode (anode), where it is oxidised to form H⁺ ions and electrons. The flow of these electrons through the circuit is what creates the potential difference (voltage).

❌ Misconception Alert

Do not say hydrogen is "burnt." While the overall reaction is the same as combustion, in a fuel cell, it happens electrochemically. The examiner is looking for the word oxidised.

Topics

Chemistry · Required Practicals · C4: Chemical Changes · C5: Energy Changes

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 1 (Higher), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.