4.3.1 The Process of Electrolysis

When an ionic compound is melted or dissolved in water, it dissociates into its constituent ions. The presence of free-moving ions in the liquid or solution enables it to conduct electricity. Such substances are known as electrolytes.

Electrolysis

Electrolysis is a process that involves the passage of an electric current through an electrolyte. This current causes the positively charged ions (cations) to move towards the negative electrode, known as the cathode, while the negatively charged ions (anions) move towards the positive electrode, known as the anode.

At the electrodes, the ions undergo chemical reactions and are discharged, resulting in the formation of new substances. This process allows for the separation of elements from their compounds. The products formed during electrolysis depend on the specific electrolyte being used.

During electrolysis, half equations can be written to represent the reactions occurring at the electrodes. These half equations show the transfer of electrons and the formation of new substances.

At the cathode (negative electrode), positively charged ions (cations) from the electrolyte are attracted and gain electrons. This reduction process leads to the formation of new substances. The half equation at the cathode represents the reduction reaction occurring. For example, in the electrolysis of molten lead(II) bromide (PbBr₂), the half equation at the cathode can be written as:

Pb²⁺(aq) + 2e^- → Pb(l)

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

At the anode (positive electrode), negatively charged ions (anions) from the electrolyte are attracted and lose electrons. This oxidation process also leads to the formation of new substances. The half equation at the anode represents the oxidation reaction occurring. Using the same example of electrolysing molten lead(II) bromide, the half equation at the anode can be written as:

2Br^-(aq) → Br₂(g) + 2e^-

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

These half equations should be balanced to ensure that the number of electrons gained and lost is equal. Balancing the half equations demonstrates the conservationThe professional care, preservation, and restoration of archaeological materials and sites, often requiring scientific expertise. of charge during the electrolysis process.