The mass of carbon anode consumed (assuming it gives only carbon dioxide gas) in the large-scale pro

Question

The mass of carbon anode consumed (assuming it gives only carbon dioxide gas) in the large-scale production of $54 \mathrm{~kg}$ of aluminium metal from bauxite by the Hall-Heroult process is (Atomic mass of $\mathrm{Al} = 27 \mathrm{~u}$)

Professor PC Thomas Classes · Answer

(d) : The overall reaction for the Hall-Heroult process is $2\mathrm{Al}_2\mathrm{O}_3 + 3\mathrm{C} ightarrow 4\mathrm{Al} + 3\mathrm{CO}_2$. According to the stoichiometry, 4 moles of Al ($4 	imes 27 = 108 \mathrm{~g}$) require 3 moles of C ($3 	imes 12 = 36 \mathrm{~g}$) to be consumed. Thus, $108 \mathrm{~kg}$ of Al requires $36 \mathrm{~kg}$ of carbon. To produce $54 \mathrm{~kg}$ of Al (which is half of $108 \mathrm{~kg}$), the mass of carbon required is $\frac{36}{2} = 18 \mathrm{~kg}$.