Electrolysis and Electrochemistry

Meaning of Electrolysis

Electrolysis is the chemical decomposition of an electrolyte (a compound that conducts electricity when molten or dissolved) by passing an electric current through it.

Key Terms

• Electrolyte – a substance that conducts electricity in molten or aqueous form and is decomposed in the process
• Electrode – a conductor (anode or cathode) through which current enters or leaves the electrolyte
• Anode – the positive electrode, where oxidation occurs and negative ions (anions) are discharged
• Cathode – the negative electrode, where reduction occurs and positive ions (cations) are discharged

How Electrolysis Works

When an electric current passes through a molten or dissolved electrolyte, positive ions move to the cathode and gain electrons (reduction), while negative ions move to the anode and lose electrons (oxidation).

Examples of Electrolysis

• Electrolysis of molten lead(II) bromide – produces lead at the cathode and bromine at the anode
• Electrolysis of acidified water – produces hydrogen at the cathode and oxygen at the anode
• Electrolysis of brine (concentrated sodium chloride solution) – produces chlorine gas, hydrogen gas and sodium hydroxide

Applications of Electrolysis

• Electroplating – coating a metal object with a thin layer of another metal, e.g. chromium plating
• Extraction of reactive metals such as aluminium and sodium
• Purification of metals such as copper

Summary

Electrolysis converts electrical energy into chemical energy to split compounds into their elements, and it has wide industrial uses in metal extraction, purification and electroplating.