ELECTROPLATING - PUNJAB-CURRICULUM-AND-TEXTBOOK-BOARD-PCTB / 10TH-CLASS / CHEMISTRY / HISTORY-OF-CHEMISTRY-10TH-CLASS-NBF-2024 / ELECTROCHEMISTRY / ELECTROPLATING

4.4 Electroplating (deposition using the same electrode).

Key Rule to Remember:

Dilute Solution: Oxygen at the anode.

Concentrated Solution: Halogen at the anode.

The cathode always produces hydrogen gas in both cases.

4.4 Electroplating (deposition using the same electrode).

The electrolytic process used to deposit one metal on another metal is called electroplating. An object can be electroplated by making it cathode in an electrolytic tank containing ions of the plating metal. The plating metal is made anode. On passing electricity through the electrolytic tanks, a thin layer of anode metal is deposited on the surface of the object.

4.4.1 Applications of Electroplating

Steel objects are often protected from corrosion by electroplating with zinc, tin and chromium.

Zinc Plating

Zinc plating on steel is done by using zinc metal as anode. A solution of potassium zinc cyanide $K_{2} [Z n (C N)_{4}]$ containing little sodium cyanide is used as an electrolyte. The steel object is made of cathode. During the electrolysis zinc at the anode enters the solution as $Z n^{2 +}$ ions, which are deposited at the cathode. The electrolyte ionizes as follows.

K_{2} [Z n (C N)_{4}]_{(a q)} \overset{2 K_{(a q)}^{+} + [Z n (C N)_{4}]^{2_{(a q)}}}{\to}

[Z n (C N)_{4}]^{2_{(a q)}} \overset{Z n^{2_{(a q)}} + 4 C N_{(a q)}^{+}}{\to}

Following reactions occur at the electrodes:

At anode:

Z n_{(s)} ⟶ Z n^{2_{(a q)}} + 2 e^{-}

At cathode:

Z n^{2_{(a q)}} + 2 e^{-} ⟶ Z n_{(s)}

Sodium cyanide prevents the hydrolysis of electrolytes.