Write a short note on electrolytic refining of copper.

Explanation

A number of metals like zinc, copper, tin, silver, aluminium etc., are refined by the process of electrolysis. Purification of an impure method by the method of electrolysis is called electrorefining. In this method the impure metal is made anode and thin sheet of the same metal in its purest from is made cathode. The electrolyte taken is usually a solution of a suitable salt of that metal mixed with corresponding acid. As a result of electrolysis positively charged metal ions go to the cathode and are deposited there after neutralising their charges. Negatively charged ions go to the anode which is impure metal and take an equivalent amount of pure metal from the impure metal anode and again change. into electrolyte. The process is continued till the whole of pure metal gets transferred to cathode. At the end whole the anode is consumed and less reactive impurities like gold and silver settle down as anode mud. On the other hand more reactive impurities like Zn, Fe, Ni etc. pass into the solution i.e., in the electrolyte. The cathode is the refined metal. It is washed, dried and put to various uses.
Suppose we are to purify copper metal by electolysis. A block to impure copper is made anode and a thin sheet of pure copper. is made cathode. An aqueous solution of copper sulphate acidified with sulphuric acid is taken as an electrolyte. The electrodes, as mentioned above, are suspended into the electrolyte with the help of some horizontal rods above the tank. As result of electrolysis, pure copper is transferred to the cathode and deposited there.
Chemistry of the process :
`CuSO_(4) (aq) hArr Cu^(2+) (aq)+SO_(4)^(2-)(aq)`
On the passage of electric current through the electrolyte solution, the `Cu^(2+)` ions travel to the cathode and are converted inte copper atoms by gaining two electrons per ion. The copper is deposited at the cathod.
`Cu^(2+)(aq)+2e^(-) to Cu(s)`
The negative sulphate ions `SO_(4)^(2-)` travel to the anode. Due to the passage of the electric current, an equivalent amount of copper get dissolved at anode.
`Cu(s) to Cu^(2+)(aq)+2e^(-)`
The `cu^(2+)` (aq) ions so produced combine with the `SO_(4)^(2-)` ions to give `CuSO_(4)` (aq), the electrolyte.
`Cu^(2+)(aq)+SO_(4)^(2-)(aq) hArr CuSO_(4)(aq)`
The above process continues till the whole of the pure metal is deposited over the cathode and impurities left behind as anode mud or in solution.