Electrolysis of Brine (WJEC GCSE Chemistry)

Manufacture of Sodium Hydroxide

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 

• 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