Identify the products formed at the electrodes and describe the observations made during the electrolysis of aqueous copper(II) sulfate using inert carbon/graphite electrodes and when using copper electrodes

Electrolysis of Aqueous Copper(II) Sulfate ⚡

In this experiment we use an electric current to split a copper‑sulfate solution into its ions and make new substances at the electrodes. Think of the solution as a soup of ions, and the electrodes as spoons that stir the soup by letting electrons flow.

Using Inert Carbon/Graphite Electrodes 🟡

Carbon is inert – it doesn’t react itself. It only allows electrons to travel from one electrode to the other.

ElectrodeReaction (Ionic)Products
Cathode (−)\$Cu^{2+} + 2e^- \rightarrow Cu(s)\$Copper metal deposits as a shiny layer on the carbon rod.
Anode (+)\$2H2O \rightarrow O2 + 4H^+ + 4e^-\$Oxygen gas bubbles rise from the anode; the solution becomes slightly acidic.

Observations:

  • Bright blue solution remains unchanged.

  • At the cathode, a dull‑red copper coating forms.

  • At the anode, small white bubbles of oxygen appear.

  • No copper dissolves from the carbon electrodes.

Exam tip: Write the net ionic equations, identify which electrode is the anode/cathode, and describe the colour and bubble observations. Remember that inert electrodes only allow electron transfer, not participation in the reaction.

Using Copper Electrodes 🟤

When the electrodes are made of copper, they can participate in the reaction – they can dissolve or deposit.

ElectrodeReaction (Ionic)Products
Cathode (−)\$Cu^{2+} + 2e^- \rightarrow Cu(s)\$Copper metal deposits on the copper cathode.
Anode (+)\$Cu(s) \rightarrow Cu^{2+} + 2e^-\$Copper ions enter the solution; the anode dissolves.

Observations:

  • No oxygen bubbles are seen – the anode dissolves instead.

  • Both electrodes become coated with copper; the anode slowly shrinks.

  • The blue colour of the solution may become slightly darker as more Cu²⁺ ions are released.

  • Current flows smoothly because copper is a good conductor.

Exam tip: Note that the anode is the electrode that dissolves. Write the dissolution reaction and explain why no oxygen is produced. Highlight the change in electrode mass and the colour of the solution.

Key Points for the Exam

  1. Identify the anode and cathode by the direction of electron flow.

  2. Write the correct net ionic equations for each electrode.

  3. Describe the visual observations (colour change, bubbles, electrode mass).

  4. Explain the role of inert vs. reactive electrodes.

  5. Use the analogy of a soup and spoons to remember that electrons are the “stirring” force.

Good luck with your studies – remember that electricity can make the invisible ions in a solution do visible work!