Electrolysis of Aqueous Sodium Chloride & Dilute Sulfuric Acid
Aqueous sodium chloride
- Brine is a concentrated solution of aqueous sodium chloride
- It can be electrolysed using inert electrodes made from platinum or carbon/graphite
- When electrolysed, it produces bubbles of gas at both electrodes as chlorine and hydrogen are produced, leaving behind sodium hydroxide solution
- These substances all have important industrial uses:
- Chlorine is used to make bleach
- Hydrogen is used to make margarine
- Sodium hydroxide is used to make soap and detergents
Product 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
Product at the Positive Electrode:
- The Cl– ions are discharged at the anode
- They lose electrons and chlorine gas forms
- The Na+ and OH– ions remain behind and form the NaOH solution
Diagram showing the products of the electrolysis of aqueous sodium chloride
Dilute sulfuric acid
- Dilute sulfuric acid can be electrolysed using inert electrodes made from platinum or carbon/graphite
- Bubbles of gas are seen at both electrodes
Product at the Negative Electrode
- H+ ions are attracted to the cathode, gain electrons and form hydrogen gas
Product at the Positive Electrode
- OH- ions are attracted to the anode, lose electrons and form oxygen gas and water
Determining what gas is produced
- If the gas produced at the anode relights a glowing splint dipped into a sample of the gas then the gas is oxygen
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
