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IN ELECTROLYSIS, IMPURE COPPER CAN BE REFINED OR MADE PURE. IF THERE ARE LOWER METALS LIKE SILVER IN THE IMPURE BLOCK OF COPPER, HOW WILL WE GET COPPER AT THE CATHODE? DUE TO SELECTIVE DISCHARGE, WON'T SILVER BE DISCHARGED AT THE CATHODE?
The most important use of copper is in the form of wire for electric transmission.For this,copper must be absolutely pure because very small amounts of impurities can reduce its conductivity in a great  extent.
Electrolyte: Aqueous copper sulphate solution acidified with dilute sulphuric acid.
Electrode:  cathode: Thin sheet of pure carbon
                     Anode:    Impure block of copper

When the current is passed through the electrolyte,the copper ions of the copper sulphate solution are attracted to the cathode where they gain electron and are deposited on the pure copper strips.The impure copper loses electrons and passes into solution as soluble copper ions.
CuSO4 Cu2+ + SO42-
H20         H+    +  OH-

At the cathode Cu2+ are discharged at the cathode as neutral copper atoms.Thus pure copper gets deposited at the cathode.
Cu2+ + 2e- Cu

At the anode SO42- and OH- migrate to the anode but neither get discharged.Instead teh copper anode itself loses eelectrons to give Cu2+ ions in solution.
Cu - 2e- Cu2+
The net result is that gradually the impure slab of copper gets used and thin strips of copper become thicker and thicker.The copper deposited at the cathode is 99.9% pure.
The impurities on the other hand settle down as anode mud or slime which contains gold and silver (which are recovered.)


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