Question

The Hall Héroult process is used to produce what?

Answer 1

Aluminium.

Explanation:

The Hall-Héroult process is probably the most common method of smelting aluminium industrially.

Alumina (or Aluminium Oxide, `Al_2O_3`), the most common aluminium oxide, undergoes electrolysis hrough the Hall-Héroult process, where alumina is dissolved in molten cryolite (`Na_3AlF_6`) for electrolysis, at around `940^@-980^@` celsius.

At the cathode:
`Al^(3+)+3e^(-) -> Al`

At the anode:
`O^(2-)+C -> CO + 2e^(-)`

Full Equation:
`Al_2O_3 + 3C -> 2Al + 3CO`

As to why the alumina must be dissolved in cryolite rather than just aqueous `Al_2O_3`: hydronium ions in the water will oxidise the elemental aluminium. You may think, "why not use molten alumina?" Well, while this would work, alumina has a melting point of around `2000^@`C. Thus it is dissolved in molten cryolite (MP `~~ 1000^@`C).

PS: natural cryolite is far too rare to be used for electrolysis, so a synthetic version is created from fluorite, a far more common material.

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