What Is Electrolysis?

Electrolysis is the process of decomposing an ionic compound using electricity.

This process occurs when an electric current passes through a molten or aqueous ionic compound, causing chemical reactions at the electrodes.

Electrolysis is an important industrial and laboratory process used to extract metals, produce chemicals, and purify substances.

What Is an Electrolyte?

An electrolyte is a substance that can conduct electricity when molten or dissolved in water.

Electrolytes contain mobile ions that carry electrical charge.

Examples of electrolytes include:

• Molten sodium chloride
• Aqueous copper sulfate
• Dilute sulfuric acid

When electricity passes through an electrolyte, the ions move toward the electrodes.

Electrodes in Electrolysis

Electrodes are solid conductors that allow electric current to enter or leave the electrolyte.

There are two types of electrodes:

Cathode

The cathode is the negative electrode.

Positive ions (cations) move toward the cathode and gain electrons.

This process is called reduction.

Anode

The anode is the positive electrode.

Negative ions (anions) move toward the anode and lose electrons.

This process is called oxidation.

Movement of Ions During Electrolysis

During electrolysis:

• Positive ions move toward the cathode
• Negative ions move toward the anode

At the electrodes, ions either gain or lose electrons to form new substances.

This leads to the chemical decomposition of the electrolyte.

Example – Electrolysis of Molten Lead(II) Bromide

Molten lead(II) bromide (PbBr₂) contains:

• Lead ions (Pb²⁺)
• Bromide ions (Br⁻)

During electrolysis:

At the cathode:

Pb²⁺ + 2e⁻ → Pb

Lead metal forms at the cathode.

At the anode:

2Br⁻ → Br₂ + 2e⁻

Bromine gas forms at the anode.

Why Electrolysis Is Important

Electrolysis is used in many industries and chemical processes.

Some important applications include:

• Extraction of reactive metals such as aluminium
• Electroplating metals for protection and decoration
• Production of chlorine, hydrogen and sodium hydroxide
• Purification of metals such as copper

These processes are essential in modern manufacturing and technology.

Key Terms in Electrolysis

TermMeaningElectrolyteSubstance that conducts electricity through ionsElectrodeConductor where reactions occurCathodeNegative electrode where reduction occursAnodePositive electrode where oxidation occurs

Understanding these terms is important for electrochemistry.

Exam Tip (5070)

Students are often asked to:

• Define electrolysis
• Identify the cathode and anode
• Describe products formed during electrolysis

Example exam question:

Define electrolysis.

Answer:

Electrolysis is the decomposition of an ionic compound when an electric current passes through it in molten or aqueous form.

Practice Question

During electrolysis, where do positive ions move?

Answer

Positive ions move toward the cathode, where they gain electrons and are reduced.

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