3.09 Electrolysis of copper sulfate

Question 1

Describe how to set up an electrochemical cell for electrolysis

Answer 1

1. Get two inert electrodes (e.g. platinum or carbon)
2. Clean the electrodes with sandpaper, then ensure you don’t touch them with your hands to avoid getting grease on them
3. Place electrodes into a beaker filled with electrolyte
4. Place two inverted test tubes filled with electrolyte over the bottom of the electrodes (to catch any gases produced)
5. Connect electrodes to a power supply using crocodile clips and wires

Question 2

What ions does copper sulfate solution contain?

Answer 2

Cu2+

SO4(2-)

H+ and OH- (from dissociated water)

Question 3

In the electrolysis of CuSO4, what is made at the cathode and anode

Answer 3

Cathode: copper metal (as copper is less reactive than hydrogen)

Anode: oxygen and water (as there are no halide ions)

Question 4

If you conduct electrolysis of copper sulfate with copper electrodes, what happens to the electrodes?

Answer 4

The mass of the cathode will increase with deposited copper, and the mass of the anode decreases due to copper being ionised.

The electric current (1) removes electrons from copper atoms at the anode (to make Cu2+) and donates electrons at the cathode to nearby Cu2+ to make copper atoms

Question 5

How is copper purified using electrolysis?

Answer 5

Make the impure copper the anode, and use a thin piece of pure copper as the cathode.

Electrolyte is copper sulfate solution

During electrolysis, the copper transfers from the impure anode to the pure cathode. Impurities from the anode sink to the bottom of the cell, forming a sludge

Question 6

How do you electrolyse an ionic substance that is not in solution?

Answer 6

1. Put solid ionic substance in a crucible
2. Heat crucible with Bunsen until it melts (in a fume cupboard to avoid release of toxic fumes)
3. When solid is melted, put two clean inert electrodes in
4. Connect to power supply with wires and clips