Electrolysis of KI

Electrolysis of KI is used to demonstrate the movement of ions in a chemical reaction. Electrolysis of an aqueous solution is carried out using inert platinum electrodes.

When dissolved in solution, the potassium iodide splits, following the equation KI→ I(-) + K(+)

Phenolphthalein indicator is added to the the mixture before the current is switched on. When the current is turned on, a pink colour is seen at the negative electrode and a brown colour appears at the positive electrode

The negative I ions attract to the positive electrode, where they are oxidised, turning it brown with the iodine build up. Reduction occurs at the negative electrode as water molecules accept electrons formed during oxidation. The OH (-) ions produced turn the phenolphthalein pink when hydrogen is evolved, as it is now basic.

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