Electrolysis of Molten Ionic Compounds (AQA GCSE Chemistry: Combined Science)

What is produced at the anode and cathode?

• Lead(II) bromide is a binary ionic compound meaning that it is a compound consisting of just two elements joined together by ionic bonding
• When these compounds are heated beyond their melting point, they become molten and can conduct electricity as their ions can move freely and carry the charge
• These compounds undergo electrolysis and always produce their corresponding element
• To predict the products of any binary molten compound first identify the ions present
• The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode
• Therefore the cathode product will always be the metal and the product formed at the anode will always be the non-metal

Electrolysis of molten lead(II) bromide

Diagram showing the electrolysis of lead (II) bromide

Method

• Add lead(II) bromide into a crucible and heat so it will turn molten, allowing ions to be free to move and conduct an electric charge
• Add two graphite rods as the electrodes and connect this to a power pack or battery
• Turn on the power pack or battery and allow electrolysis to take place
• Negative bromide ions move to the positive electrode (anode) and lose two electrons to form bromine molecules. There is bubbling at the anode as brown bromine gas is given off
• Positive lead ions move to the negative electrode (cathode) and gain electrons to form grey lead metal which deposits on the bottom of the electrode

What are the products at the anode and cathode?

• Anode: Bromine gas
• Cathode: Lead metal