# Chemistry (PLZ HELP)

posted by Anonymous

Aluminium can be produced by the thermal decomposition of aluminium oxide. What mass of aluminium would be produced from 3.5kg of aluminium oxide?

1. MathMate

Aluminium oxide: Al2O3.
Molecular mass (approx.)=27*2+3*16=102
Aluminium:
Al
Molecular mass=27.

Write down the equation:
2Al2O3 -> 4Al + 3O2 (electrolysis)

So
2 Al2O3 molecules -> 4 Al molecules.
2*102 Al2O3-> 4*27 Al
204 : 108

Use proportion to solve for the final answer (substitute the exact atomic masses)

2. DrBob222

There is nothing wrong with the solution by MathMate of this hypotehtical question. However, I just don't believe Al2O3 will decompose thermally to Al/

3. MathMate

Quite right Dr.Bob. Thank you for the note.
It just doesn't decompose like that. Carbon is required to reduce the oxide.
Namely
2Al2O3+3C -> 4Al + 3CO2
The electrolysis part is more to help prevent the formation of CO.
However, as you said, the ratio of Al and Al2O3 does not change.

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