Electrolysis of Aqueous Sodium Chloride and Dilute Sulfuric Acid | Chemistry for Grade 11 (IGCSE) PDF Download

Aqueous sodium chloride 

• Brine is a concentrated solution of aqueous sodium chloride
• It can be electrolyzed using inert electrodes made from platinum or carbon/graphite
• During electrolysis, gas bubbles are produced at both electrodes, resulting in the formation of chlorine and hydrogen, with sodium hydroxide solution left behind
• These substances have significant industrial applications: Chlorine for bleach production, hydrogen for margarine production, and sodium hydroxide for soap and detergent manufacturing

Uses of Chlorine, Hydrogen, and Sodium Hydroxide

• Chlorine is utilized in the production of bleach.
• Hydrogen is essential in the manufacturing of margarine.
• Sodium hydroxide is a key component in the creation of soaps and detergents.

Products at the Electrodes during Electrolysis of Brine

At the Negative Electrode

• Hydrogen ions (H⁺) are discharged at the cathode due to their lower reactivity compared to sodium ions.
• These H⁺ ions accept electrons, forming hydrogen gas.

At the Positive Electrode

• Chloride ions (Cl^-) are discharged at the anode.
• Upon losing electrons, chlorine gas is produced.
• Sodium (Na⁺) and hydroxide (OH^-) ions remain, yielding sodium hydroxide (NaOH) solution.

Diagram showing the products of the electrolysis of aqueous sodium chloride

Electrolysis of Dilute Sulfuric Acid

• Dilute sulfuric acid can undergo electrolysis using inert electrodes like platinum or carbon/graphite.
• Bubbles of gas are observed at both the cathode and anode.

Product at the Negative Electrode

• Hydrogen ions (H⁺) migrate to the cathode, gain electrons, and produce hydrogen gas.

Product at the Positive Electrode

• Hydroxide ions (OH^-) are attracted to the anode, lose electrons, and yield oxygen gas along with water.
• To determine the gas produced, if the gas at the anode reignites a glowing splint, then it's confirmed to be oxygen gas.
  Diagram showing the test for oxygen gas
  
• If the gas produced at the anode bleaches damp litmus paper, then the gas is chlorine.
  Diagram showing the test for chlorine gas
  
• If the gas produced at the cathode burns with a 'pop' when a sample is lit with a lighted splint, then the gas is hydrogen.
  Diagram showing the test for hydrogen gas