| Copper is a very unreactive metal - it's below even hydrogen in the reactivity series. This means it won't even react with water. For this reason, copper is obtained very easily from its ore by reduction with carbon.
However, this copper isn't pure enough for use in electrical conductors. The purer the copper is, the better it will conduct. Electrolysis is used to obtain very pure copper.
Cathode |
---------------| |------------- Anode
| | |
--- ------
| | | |
| | Cu2+ | |
| | | |
| | | |
| | | |
--- |-----
------------
/ Sludge \
-------------------------------------------
The cathode starts as a very thin piece of pure copper and more pure copper adds to it. The anode is just a big lump of impure copper which will dissolve. The "sludge" is all the impurities.
The reaction at the cathode -
Cu2+(aq) + 2s- -> Cu(s)
The reaction at the anode -
Cu(s) -> Cu2+ + 2e-
The electrical supply acts by pulling electrons off the copper atoms at the anode, causing them to become Cu2+ ions. It then offers the electrons at the cathode to nearby Cu2+ ions to turn them back into copper atoms. The impurities are dropped off, and pure copper bonds to the cathode.
This process can go on for weeks, with the cathode often twenty times bigger by the end. | 
