How are metals refined by the electrolytic process? Describe the electrolytic refining of copper with the help of a neat labelled diagram.
The process of electrolysis is used in electrolytic refining. This is the most widely used method for the refining of impure metals. Several metals like copper, zinc, tin, lead, nickel, chromium, gold, silver are refined by this process.
Electrolytic refining of copper:
An electrolytic refining tank consists of an anode, a cathode and an electrolyte (acidified copper sulphate solution). A thick rod of an impure metal is made the anode and attached to the positive terminal. A thin rod of a pure metal is made the cathode and attached to the negative terminal. When electricity is passed through the cell, impure metal from the anode gets dissolved in the electrolyte. The metal ions from the electrolyte move to the cathode and get deposited there as pure metal. While the soluble impurities dissolve in the electrolyte, the insoluble ones deposit under the anode as anode mud.
When electricity is passed through the electrolytic cell, following reactions take place at the anode and cathode:
(i) Impure copper atoms from the anode lose two electrons to form copper ions and enter copper sulphate electrolyte.
Copper ions from the copper sulphate electrolyte move to the cathode (negatively charged) by gaining two electrons from the cathode. Thus, they get reduced to copper atoms.
As the process continues, the cathode (pure metal collected) progressively becomes thicker and anode (impure metal) keeps getting thinner. The metal obtained is 99.99 percent pure.