Question

Write the anode and cathode reaction in electrolysis of copper sulphate solution using copper electrodes

Answer 1

Using Graphite Rods
1. Set up an electrolysis cell using graphite rods as electrodes and copper(II) sulphate solution as electrolyte.
2. At the anode: Bubbles of gas (oxygen) are formed at the anode.
Anode reaction: 4OH-(aq) → O2(g) + 2H2O(l) + 4e- 
3. At the cathode: A deposit of copper forms on the cathode; this will often be powdery and uneven. 
Cathode reaction: Cu2+(aq) + 2e- → Cu(s)

Using Copper Plates (Refining Copper)
1. Replacing the graphite rods with clean copper plates produces a different anode reaction. 
2. At the anode: No oxygen is produced, rather the copper anode dissolves.
Anode reaction: Cu(s) → Cu2+(aq) + 2e- 
3. At the cathode: A deposit of copper forms on the cathode.
Cathode reaction: Cu2+(aq) + 2e- → Cu(s)

Answer 2

Answer:

The change involves two electrons per copper atom. When copper electrodes are used in the electrolysis of copper sulfate solution, the mass loss of copper from the positive anode electrode should equal the mass of copper gained and deposited on the negative cathode electrode.