Predict that oxygen is produced at the anode unless the solution contains halide ions.

During the electrolysis of aqueous solutions, oxygen is typically produced at the anode. This occurs because water molecules can dissociate into hydroxide ions (OH⁻) and hydrogen ions (H⁺), and the oxidation of these hydroxide ions leads to the formation of oxygen gas. However, if halide ions such as chloride (Cl⁻), bromide (Br⁻), or iodide (I⁻) are present in the solution, they will be preferentially oxidized at the anode, resulting in the production of chlorine, bromine, or iodine instead of oxygen. Thus, the presence of halide ions alters the expected product at the anode during electrolysis.