(a) Electroplating, is also known as electrodeposition, a process for producing a thin and firm layer of material (such as metal) onto a surface using electric current.
(b) The coating produced is primarily served as a decorative or corrosion protective purposes, or enhancing the specific properties of the surface.
(c) Some of the well-known industrial applications of electroplating are copper plating for printed circuit boards interconnection and chrome-plating of steels parts on automobiles.
|Copper plating for printed circuit board interconnection|
|Chrome-plating of alloy wheels on automobiles|
(d) In electroplating process, the cathode is the part (or workpiece) to be plated, such as copper. The anode is the metal that is to be deposited. A solution of its metal salt is used as the electrolyte in the electrolytic cell.
(e) At anode, copper anode is oxidised and dissolved to form Cu2+ ions since an active electrode is used.
Cu (s) → Cu2+ (aq) + 2e-
Cu2+ (aq) + 2e- → Cu (s) E = +0.34 V
2 H2O + 2e- → H2 (g) + 2 OH- (aq) E = -0.83 V
(f) At cathode, Cu2+ ions are preferentially reduced than water molecules due to its more positive Eo value. Thus, copper metal is formed and plated onto the cathode surface.
(g) This results to an effective transfer of copper from anode surface to a plate coating at cathode. Since there is a continuous supply of Cu2+ ions from anode, the concentration of the aqueous CuSO4 remains unchanged.
Notes: Additional reading on electroplating
2. Purification of metals
(a) Purification of metals is a process involving the removal of metal impurities from impure metals.
(b) It is commonly used to extract metals from its ores, such as copper from its ore.
(c) In the purification of copper, the cathode is a strip of pure copper. The anode is a block of impure copper. A solution of its metal salt (CuSO4) is used as the electrolyte in the electrolytic cell.
(d) At anode, copper anode is oxidised and dissolved to form Cu2+ ions.
Cu (s) → Cu2+ (aq) + 2e-
(e) At cathode, Cu2+ ions are preferentially reduced than water molecules due to its more positive Eo value.
Cu2+ (aq) + 2e- → Cu (s)
(f) Any impurities (or less reactive metal) in the impure copper fall to the bottom of the cell and a sludge is formed. This sludge may contain valuable metals such as silver and gold.
(g) Impurities (or more reactive metal) such as zinc and aluminium tend to dissolve in the solution by forming ions at the anode. But, these ions are reduced at the cathode (due to their more negative Eo value) unless they exist in a very high concentration.