Question

In the metallurgy of aluminium:

• A. ${Al}^{3+}$ is oxidised to $A{l}_{\left(s\right)}$
• B. graphite anode is oxidised to carbon monoxide and carbon dioxide
• C. the oxidation state of oxygen changes in the reaction at anode
• D. the oxidation state of oxygen changes in the overall reaction involved in the process

Answer 1

The correct option is B graphite anode is oxidised to carbon monoxide and carbon dioxide

The oxidation state of $O$ does not change in either the reaction occuring at the anode or the overall reaction as shown below:

At anode:

$C+O^{2-}\to \stackrel{2+2-}{CO}+2e^{-};CO+O^{2-}\to \stackrel{4+2-}{C{O}_2}+2e^{-};C+2O^{2-}\to \stackrel{4+2-}{C{O}_2}+4e^{-}$

At cathode:

$A{l}^{3+}+3e^{-}\to Al$

Overall reaction:

$\stackrel{3+2-}{2A{l}_2{O}_3}+3C\to 4Al+\stackrel{2+2-}{3C{O}_2}$

Hence, option B is correct.