Purifying Copper
How can impure copper be purified using electrolysis?
The positive electrode (anode) is made of impure
copper which needs to be purified. The negative
electrode (cathode) is a bar of pure copper. The two
electrodes are placed in a substance of copper sulfate.
Copper ions leave the anode and are attracted to the
cathode, where they are deposited as copper atoms.
The pure copper cathode increases in size, while the
anode goes away. The part left behind form a sludge.
[Source 1]
What happens at the anode and the cathode and the
reactions at each electrode?
Positive ions are attracted to negative electrodes and
gain electrons and are reduced. Negative ions are
attracted to the positive electrode and loose electrons so
are oxidised (this is called oxidation). The electrolyte
copper sulfate, has a high concentration of copper(II)
ions Cu2+ and sulfate ions SO42– to carry the current
during the electrolysis process. There are small
concentrations of hydrogen ions H+ and hydroxide ions
(OH–) from the self-ionisation of water itself, but these
can be ignored in this experiment.
The electrolysis will only take place when electricity is
passed through the copper solution.
The technical details of the electrolysis of copper
sulfate solution with two different electrodes (a)
graphite (carbon) electrodes and (b) copper electrodes
are all explained below