In the electrolytic production of aluminium metal from alumina (Al2O3), the alumina is dissolved in cryolite (Na3AlF6). The anodes and cathodes are made of carbon. The electrode reactions may be represented by: C + 2O^{2-} → CO2 + 4e^- Al^{3+} + 3e^- → Al The net reaction for this electrolysis process is A. 2Al2O3 → 4Al + 3O2 B. Al^{3+} + C + 2O^{2-} → Al + CO2 C. 2Al2O3 + 3C → 4Al + 3CO2 D. 4Al^{3+} + 6O^{2-} + 2C → 2Al2O3 + CO2

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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

Question 3

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In the electrolytic production of aluminium metal from alumina (Al2O3), the alumina is dissolved in cryolite (Na3AlF6). The anodes and cathodes are made of carbon. T... show full transcript

Worked Solution & Example Answer: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

Step 1

The net reaction for this electrolysis process is

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Answer

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

The reduction reaction of aluminum ions is given by:

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

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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

Worked Solution & Example Answer: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

The net reaction for this electrolysis process is

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