Electrolysis of Molten Ionic Compounds

Ionic compounds are usually solid at room temperature and have a rigid structure, which means their ions can’t move freely. As a result, ionic compounds can’t conduct electricity in their solid state and can’t undergo electrolysis.

However, molten ionic compounds can conduct electricity as their ions are free to move. For example, let’s look at the electrolysis of lead (II) bromide.

Lead (II) bromide is a solid at room temperature. So, it can’t conduct electricity, as the ions cannot move freely. However, we can produce bromine and lead using the following process:

1. Add lead(II) bromide to a crucible and heat it over a Bunsen burner until it melts and becomes a liquid.

  • Once melted, the ions can move freely, turning it into an electrolyte.

2. Insert two graphite rods as electrodes into the molten ionic compound.

3. Connect the electrodes to a power supply and turn it on to start the electrolysis process.

During electrolysis, the molten electrolyte splits into its constituent elements, which are deposited at the electrodes.

  • The positive ions are attracted to the negative cathode, so the metal will form at the cathode
  • The negative ions are attracted to the positive anode, so the non-metal element will form at the anode

As a result of the electrolysis, lead and bromine are produced.

At the Negative Cathode

The lead cations (Pb²⁺) are attracted to the negative cathode. Here, they will gain electrons and transform into neutral lead atoms, forming a grey coating on the cathode.

As the lead ion (Pb²⁺) has a +2 charge, it will require two electrons to become neutral.

At the Positive Anode

The bromide anions (Br⁻) are attracted to the positive anode. Here, they will each lose an electron to become neutral bromine atoms, which are released as a brown gas.