What is produced at the anode if there are no halogen ions present?

When electrolysis occurs and there are no halogen ions present, the predominant reaction at the anode involves the formation of oxygen gas. This happens because, in the absence of halide ions like chloride or bromide, water molecules are oxidized instead.

During the process of electrolysis, water can dissociate into hydroxide ions and hydrogen ions. At the anode, the hydroxide ions (from water) lose electrons and are converted to oxygen gas and water. The overall half-equation for this reaction can be represented as:

4OH⁻ → O₂ + 2H₂O + 4e⁻.

This reaction demonstrates that oxygen gas is generated when water is the source of ions during electrolysis. Therefore, when halogen ions are not available to be preferentially oxidized, oxygen becomes the product formed at the anode.