Question

in a electrolytic tank aluminium metal is being extracted by d electrolysis of molten aluminium oxide using carbon electrodes.Ot is observed that one of the carbon electrodes is gradually burnt away and has to be replaced
i)Which carbon electrode is burnt away and Why?
Briefly explain

Answer 1

The diagram shows an aluminium oxide electrolysis tank. Both the negative electrode (cathode) and positive electrode (anode) are made of graphite, a form of carbon.

Aluminium metal forms at the negative electrode and sinks to the bottom of the tank, where it is tapped off.

Oxygen forms at the positive electrodes. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, and they gradually burn away

The formation of Carbon di oxide make the anode burn because during the electrolysis process, aluminium is deposited at the cathode and oxygen is liberated at the anode. Some of this oxygen reacts with the carbon in the graphite to form carbon-dioxide, thus slowly burning away the anodes. Thus, the anodes have to replaced periodically.