In the electrolytic production of aluminium metal from alumina (Al2O3), the alumina is dissolved in cryolite (Na3AlF6) - VCE - SSCE Chemistry - Question 3 - 2004 - Paper 1

To derive the net reaction from the given half-reactions, we recognize that:

1. The reduction reaction of aluminum ions is given by:

   $ext{Al}^{3+} + 3e^- \rightarrow \text{Al}$

2. The oxidation reaction of carbon is:

   $\text{C} + 2\text{O}^{2-} \rightarrow \text{CO}_2 + 4e^-$

Now balancing these reactions requires that we have equal numbers of electrons exchanged. We can multiply the aluminum reduction by 4 and the carbon oxidation by 3 to balance the electrons:

• From $4 \text{Al}^{3+} + 12e^-$
• From $3 \text{C} + 6\text{O}^{2-} \rightarrow 3\text{CO}_2 + 12e^-$

After combining these:

$4\text{Al}^{3+} + 3\text{C} + 6\text{O}^{2-} \rightarrow 4\text{Al} + 3\text{CO}_2$

Now rearranging gives us the balanced overall reaction stated in option C:

C. 2Al2O3 + 3C → 4Al + 3CO2.