Question

Why do anodes need to be replaced from time to time during the electrolysis of alumina?

Hint:

Remember: The consumption of carbon anodes is due to the reaction of oxygen with the carbon, forming carbon dioxide, which gradually reduces the anode's size.

Answer 1

During the electrolysis of alumina (Al₂O₃), aluminum metal is produced at the cathode, and oxygen gas is released at the anode. The anodes are typically made of carbon (graphite), and over time, the oxygen produced at the anode reacts with the carbon. This reaction forms carbon dioxide gas (CO₂), which causes the anode to gradually burn away and get consumed. The reaction at the anode is: 2 O²⁻ → O₂(g) + 4e^- The oxygen gas formed reacts with the carbon anode: C + O₂(g) → CO₂(g) As the carbon is consumed, the anodes need to be replaced periodically to ensure the continuous operation of the electrolysis process. Without regular replacement, the anodes would wear out and eventually break down.
Thus, the anodes need to be replaced from time to time during the electrolysis of alumina due to the consumption of carbon in the reaction with oxygen.