Electrolysis of Sodium Chloride (Oxford AQA IGCSE Combined Science Double Award)

Electrolysis of Sodium Chloride

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^–

  • OH^–

Reaction at the Negative Electrode:

• The H⁺ ions are discharged at the cathode as hydrogen is less reactive than sodium

• The H⁺ ions gain electrons (reduction)to form hydrogen gas 

2H⁺ + 2e^– → H₂

Reaction at the Positive Electrode:

• The Cl^– ions are discharged at the anode 

• They lose electrons (oxidation) and chlorine gas forms

2Cl^– → Cl₂  +  2e^–

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

The production of sodium hydroxide