4.3.2 Electrolysis of Molten Ionic Compounds

When a simple ionic compound, such as lead bromide (PbBr₂), is electrolysed in the molten state using inert electrodes (electrodes that do not react or participate in the electrolysis), the compound undergoes a chemical change. This process is known as electrolysis.

During electrolysis, the ionic compound is broken down into its constituent elements due to the flow of electric current. At the cathode (negative electrode), the positive metal ions from the ionic compound are attracted and undergo reduction, gaining electrons to form the metal. In the case of lead bromide, lead ions (Pb²⁺) are reduced at the cathode:

Pb²⁺(l) + 2e^- → Pb(l)

This half-equation shows that lead ions gain two electrons to form liquid lead.

At the anode (positive electrode), the negative non-metal ions from the ionic compound are attracted and undergo oxidation, losing electrons. In the case of lead bromide, bromide ions (Br^-) are oxidised at the anode:

2Br^-(l) → Br₂(g) + 2e^-

This half-equation shows that bromide ions lose two electrons to form bromine gas.

Therefore, during the electrolysis of molten lead bromide, lead metal is produced at the cathode, while bromine gas is produced at the anode.

The products of electrolysis in molten ionic compounds depend on the specific compound being electrolysed. The metal component of the ionic compound will be produced at the cathode, while the non-metal component will be produced at the anode. By understanding the nature of the ionic compound and the reactivity of its constituent elements, you can predict the products of electrolysis.

The ability to predict the products of electrolysis relies on understanding the concept of oxidation and reduction, as well as the behaviour of different ions. Consider the following factors when predicting the products:

• Ion Charges: Determine the charges of the ions present in the molten ionic compound. Positive metal ions will be attracted to the cathode, while negative non-metal ions will be attracted to the anode.
• Reactivity: Consider the relative reactivity of the metal and non-metal components of the ionic compound. The more reactive element is more likely to be produced at the cathode, while the less reactive element is more likely to be produced at the anode.
• Standard Electrode Potentials: Consider the standard electrode potentials of the elements involved. The element with the more positive standard electrode potential is more likely to be reduced at the cathode, while the element with the more negative standard electrode potential is more likely to be oxidised at the anode.