Electrolysis of Brine (WJEC GCSE Chemistry)

Higher Tier

How is sodium hydroxide produced?

• Brine is a concentrated solution of aqueous sodium chloride
• When electrolysed, it produces chlorine and hydrogen at the electrodes leaving behind sodium hydroxide solution

Industrial Uses of the Products 

Substance	Used to make
chlorine	bleach
hydrogen	margarine
sodium hydroxide	soap and detergents

• The electrolyte is concentrated sodium chloride which contains the following ions: Na⁺, H⁺, Cl^– and OH^–

Reaction at the Negative Electrode:

• The H⁺ ions are discharged at the cathode as they are less reactive than sodium ions
• The H⁺ ions gain electrons to form hydrogen gas 

2H⁺ + 2e^– → H₂

Reaction at the Positive Electrode:

• The Cl^– ions are discharged at the anode 
• They lose electrons and chlorine gas forms

2Cl^– → Cl₂  +  2e^–

• The Na⁺ and OH^– ions remain behind and form the NaOH solution

 The production of sodium hydroxide

Diagram showing the products of the electrolysis of brine