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1CH0 · CP3.31Core practical investigationsCore

CP3.31: Inert and Copper Electrodes

In an electrolytic cell, an external supply drives a chemical change. The cathode is negative and the anode positive in this arrangement. Cations move toward the cathode and anions toward the anode, while electrons move through the external conducting circuit. Do not describe electrons as crossing the bulk solution in place of ions.

35 min Video by Science School Core practical investigations
Edexcel Core Practical 9-1 GCSE C3.31 Electrolysis of Copper Sulphate using Copper electrodesCurated by Kepler, not produced by us. Watch it before the notes below.
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Before you start

  • Use your teacher’s tier checklist: this overview can include Higher-only material, and is not a tier-specific revision list.
  • Pearson Edexcel separate GCSE Chemistry 1CH0. Preserve the specification’s core-practical reference and any explicitly required subparts.
  • Distinguish ions from electrons and recall oxidation and reduction.
  • Use the centre’s approved supervised method, apparatus, heating and disposal arrangements. Written preparation does not replace performing and recording the practical activities.

Watch, pause, try

Video by Science School. The main video focuses on copper electrodes. The written guide also covers the required inert-electrode products, and compares current with electrode mass change over a fixed time.

Viewing focus: Explain electrode polarity and charge movement

After watching, attempt these questions before opening the answers. You can also use the written lesson below.

After watching 1: Why can a copper anode lose mass while the cathode gains mass?

Show answer and reasoning

Copper atoms can lose electrons to form ions at the anode while copper ions gain electrons to form metal at the cathode.

After watching 2: Why must deposition time be controlled when comparing current?

Show answer and reasoning

Charge transfer depends on both current and time. Changing both would weaken an inference about current and the measured mass change.

What you'll be able to do

  • Explain electrode polarity and charge movement
  • Use observations and appropriate tests to identify products
  • Distinguish inert electrodes from reacting copper electrodes
1

Follow the two types of charge carrier

In an electrolytic cell, an external supply drives a chemical change. The cathode is negative and the anode positive in this arrangement. Cations move toward the cathode and anions toward the anode, while electrons move through the external conducting circuit. Do not describe electrons as crossing the bulk solution in place of ions.

At the cathode, reduction involves gain of electrons. At the anode, oxidation involves loss of electrons. In aqueous solutions, water-derived species can also be involved, so the dissolved salt’s name alone does not identify every product. Use the stated electrolyte, concentration and electrode material.

2

Use observations and tests rather than guesses

Record bubbles, colour changes or deposits at identified electrodes. Where gases are collected or tested, use the centre’s approved small-scale method and the appropriate evidence: a hydrogen pop test, oxygen relighting a glowing splint, or chlorine bleaching damp indicator paper are distinct observations. Avoid treating bubbles alone as a unique gas identification.

With aqueous copper(II) sulfate and suitable inert electrodes, copper can deposit at the cathode while oxygen forms at the anode. The half-equation Cu²⁺ + 2e⁻ → Cu explains copper formation. For a different electrolyte or electrode, check the product rules and evidence again rather than copying the same labels.

A schematic electrolytic cell has a positive inert anode on the left and a negative cathode on the right. In the stated copper sulfate example, oxygen is produced at the anode and copper deposits at the cathode.
Scroll the diagram to see the full view.
Original aqueous copper(II) sulfate example with inert electrodes. The supply drives the reaction. Ions carry charge in the electrolyte, while electrons pass through the external circuit; product rules depend on the solution and electrodes.
3

Recognise when the electrode is a reactant

Copper electrodes in copper(II) sulfate provide a different anode process from inert graphite. Copper atoms can form copper ions at the anode while copper ions are reduced at the cathode. Compare the electrode masses using consistent washing and drying; retained solution can distort an apparent mass gain.

When comparing current, control the measurement interval, electrolyte and relevant geometry. Quantitative changes require actual initial and final masses, not a claim that blue colour alone measures deposited copper. In a suitable ideal model, charge is current × time, but interpret the measurements with electrode reactions and possible experimental losses.

Current / ATime / sIllustrative cathode mass gain / g
0.203000.020
0.403000.039
0.603000.060
Scroll horizontally to see the full code or table.
Original illustrative measurements, not student results. Control time, clean and dry electrodes consistently, and plot mass change against current.
4

Worked applications

Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.

Example 1An electrode changes from 5.320 g to 5.456 g. Calculate its mass change.
1Final − initial = 5.456 − 5.320.
2The positive sign represents a gain.
Answer
+0.136 g.
Example 2Two runs use the same current, with times 120 s and 240 s. Under a stated ideal deposition model, compare the transferred charges.
1Q = It.
2At fixed current, doubling time doubles charge.
Answer
The second run transfers twice the charge under the stated conditions; use measurements to evaluate actual deposition.

Common mistakes to avoid

Identifying a gas only because bubbles appeared.
Use the appropriate test and electrode context.
Calling the anode negative in this electrolytic setup.
State the cell type and supply connections.

Key takeaways

  • You can explain electrode polarity and charge movement.
  • You can use observations and appropriate tests to identify products.
  • You can distinguish inert electrodes from reacting copper electrodes.

Apply it in an exam

Question 1: Two runs use the same current, with times 120 s and 240 s. Under a stated ideal deposition model, compare the transferred charges.

Show answer and reasoning

The second run transfers twice the charge under the stated conditions; use measurements to evaluate actual deposition.

  • Q = It.
  • At fixed current, doubling time doubles charge.

Explore further

Return to this tomorrow

Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.

  • What carries charge through the bulk electrolyte?
  • Why does changing graphite to copper matter?

Test yourself

Answer a few questions, then review anything you missed.

Next step

Keep practising

Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.

Browse practice topics

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