CHAPTER 4. ELECTROCHEMICAL REACTIONS 4.6
Electroplating ESCCB
Electroplating is the process of using electricalcurrent to coat an electrically conduc-
tive object with a thin layer of metal. Mostly, this application is used todeposit a layer
of metal that has somedesired property (e.g. abrasion and wear resistance, corrosion
protection, improvement of aesthetic qualities etc.) onto a surface that doesn’t have that
property. Electro-refining (also sometimes called electrowinning is electroplating on a
large scale. Electrochemical reactions are used to deposit pure metals from their ores.
One example is the electrowinning of copper.
Copper plays a major role in the electrical industry as it is very conductiveand is used in
electric cables. One of the problems though is that copper must be pureif it is to be an
effective current carrier.One of the methods used to purify copper, is electrowinning.
The copper electrowinning process is as follows:
- Bars of crude (impure) copper containing other metallic impurities is placed on
the anodes. - The cathodes are made up of pure copper with few impurities.
- The electrolyte is a solution of aqueous CuSO 4 and H 2 SO 4.
- When current passesthrough the cell, electrolysis takes place. The impure cop-
per anode dissolves toform Cu2+ions in solution. Thesepositive ions are at-
tracted to the negativecathode, where reduction takes place to produce pure
copper metal. The reactions that take place areas follows:
At the anode:Cu (s)→ Cu2+(aq) + 2e−At the cathode:Cu+2(aq) + 2e−→ Cu (s) (> 99%purity)- The other metal impurities (Zn, Au, Ag, Fe and Pb) do not dissolveand form a
solid sludge at the bottom of the tank or remainin solution in the electrolyte.