Electroplating

Electroplating

The electrolytic cell can be used for electroplating.

Electroplating occurs when an electrically conductive object is coated with a layer of metal using electrical current. Sometimes, electroplating is used to give a metal particular properties or for aesthetic reasons:

• corrosion protection

• abrasion and wear resistance

• the production of jewellery

a) An electroplated piece of aluminium artwork and b) a wax stool electroplated in copper.

Electro-refining (also sometimes called electrowinning) is electroplating on a large scale. Copper plays a major role in the electrical industry as it is very conductive and is used in electric cables. One of the problems though is that copper must be pure if it is to be an effective current carrier. One of the methods used to purify copper, is electrowinning (copper ore is processed into impure blister copper, which is then deposited as pure copper through electroplating). The copper electrowinning process is as follows:

1. A bar of \(\color{copperone}{\textbf{impure}}\) copper containing other metallic impurities acts as the \(\color{blue}{\textbf{anode}}\).

2. The \(\color{red}{\textbf{cathode}}\) is made up of \(\color{coppertwo}{\textbf{pure}}\) copper with few impurities.

3. The electrolyte is a solution of aqueous \(\text{CuSO}_{4}\) and \(\text{H}_{2}\text{SO}_{4}\).

   

   A simplified diagram to illustrate what happens during the electrowinning of copper.

4. When current passes through the cell, electrolysis takes place:

   • The \(\color{copperone}{\textbf{impure copper anode}}\) oxidises to form \(\text{Cu}^{2+}\) ions in solution. The \(\color{blue}{\textbf{anode decreases in mass}}\).

     \(\color{copperone}{\textbf{Cu(s)}} \to\) \(\text{Cu}^{2+}(\text{aq}) + 2\text{e}^{-}\)

   • At the cathode reduction of positive copper ions takes place to produce \(\color{coppertwo}{\textbf{pure copper metal}}\). The \(\color{red}{\textbf{cathode}}\) \(\color{red}{\textbf{increases in mass}}\).

     \(\text{Cu}^{2+}(\text{aq}) + 2\text{e}^{-}\) \(\to \color{coppertwo}{\textbf{Cu(s)}}\) (\(>\)99% purity)

5. The other metal impurities do not dissolve (\(\text{Au}(\text{s})\), \(\text{Ag}(\text{s})\)) and form a solid sludge at the bottom of the tank or remain in solution (\(\text{Zn}(\text{aq})\), \(\text{Fe}(\text{aq})\) and \(\text{Pb}(\text{aq})\)) in the electrolyte.