Application of electrolysis

Electrolysis is used in various industries for metal extraction, purification, and electroplating.

1. Key Applications of Electrolysis

• Electroplating – Coating objects with a thin metal layer.
• Production of chemicals – Chlorine gas, hydrogen gas, sodium hydroxide (chlor-alkali industry).
• Metal extraction – Obtaining metals like aluminium from ores.
• Metal refining – Purifying metals like copper.

2. Electroplating

Definition

• Electroplating is the process of coating a metal object with a thin layer of another metal using electrolysis.
• This prevents corrosion, enhances appearance, and reduces costs.

How Electroplating Works

• The object to be plated is the cathode (negative electrode).
• The metal to be deposited is the anode (positive electrode).
• The electrolyte contains ions of the plating metal.

Example: Electroplating a Spoon with Silver

• Cathode (spoon): $\text{Ag}^+ + e^- \rightarrow \text{Ag}$

• Anode (silver): $\text{Ag} \rightarrow \text{Ag}^+ + e^-$

• Overall Reaction: Silver is transferred from the anode to the spoon.

Uses of Electroplating

• Jewellery – Gold/silver coating on cheaper metals.
• Cutlery – Silver coating on utensils.
• Car parts – Chromium plating for durability.

3. Refining of Copper

Why Copper Needs Refining

• Impure copper (from ore) contains unwanted metals.
• Purification is done using electrolysis to obtain pure copper.

Electrolytic Cell for Copper Refining

• Anode (impure copper): Copper dissolves into solution.
• Cathode (pure copper): Copper ions deposit as solid metal.
• Electrolyte: Copper(II) sulphate solution.

Reactions

• At the anode (oxidation): $\text{Cu} \rightarrow \text{Cu}^{2+} + 2e^-$

• At the cathode (reduction): $\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$

• Overall: Copper is purified while impurities settle as sludge.

4. Extraction of Aluminium from Bauxite

Why Aluminium Needs Electrolysis

• Aluminium is extracted from bauxite ore as $Al₂O₃.$
• Aluminium oxide has a high melting point $(>2000°C)$, so cryolite $(Na₃AlF₆)$ is added to lower the melting point.
• Electrolysis is used to separate aluminium metal from oxygen.

Electrolytic Cell for Aluminium Extraction

• Anode (carbon electrodes): Oxidation of oxygen ions.
• Cathode (molten aluminium): Reduction of aluminium ions.

Reactions

• At the anode (oxidation): $2O^{2-} \rightarrow O_2 + 4e^-$

• At the cathode (reduction): $Al^{3+} + 3e^- \rightarrow Al$

• Overall: Molten aluminium sinks to the bottom, and oxygen gas is released.

Environmental Impact

• High energy consumption – Increases production costs.
• Carbon emissions – Carbon electrodes burn, releasing $CO₂$.
• Fluoride pollution – Toxic waste disposal issues.

5. Key Takeaways

• Electroplating enhances metal durability and appearance.
• Copper refining removes impurities via electrolysis.
• Aluminium extraction requires high temperatures and energy.
• Electrolysis is widely used in industry but has environmental consequences.