Question

The mass of carbon anode consumed (giving the only carbon dioxide) in the production of 270 kg of aluminium metal from bauxite by the Hall process is: [Atomic mass of Al=27]
A. 180 kg
B. 270 kg
C. 540 kg
D. 90 kg

Answer 1

Hint: The scientific method of extraction of minerals from its ores is termed as metallurgy. Aluminium is the metal obtained from its ores, known as bauxite.

Complete step by step answer:
The Hall-Heroult process is the most common method of extraction of aluminium from bauxite ore. In this process, pure ${\rm{A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}$ is mixed with ${\rm{Ca}}{{\rm{F}}_{\rm{2}}}$ to lower the melting point of the mixture and increases power to conductivity. Then the mixture is electrolysed to obtain aluminium.
The reaction occurs at anode is,
${\rm{A}}{{\rm{l}}^{3 + }} + 3{e^ - } \to {\rm{Al}}\left( l \right)$
The reaction occurs at anode is,
${\rm{C}}\left( s \right) + {{\rm{O}}^{2 - }} \to {\rm{CO}}\left( g \right) + 2{e^ - }$
${\rm{C}}\left( s \right) + 2{{\rm{O}}^{2 - }} \to {\rm{C}}{{\rm{O}}_2}\left( g \right) + 4{e^ - }$
The overall reaction can be written as follows:

${\rm{2A}}{{\rm{l}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}} + 3{\rm{C}} \to {\rm{4Al}} + {\rm{3C}}{{\rm{O}}_2}$ …… (1)

Now, we have to calculate the mass of Aluminium and carbon from the above reaction.
For equation (1), mass of carbon is $3{\rm{C}} = 3 \times 12 = 36$.
Similarly, we have to calculate the mass of aluminium $4{\rm{Al}} = 4 \times 27 = 108$.
So, to produce 108 kg of aluminium, 36 kg of carbon required. Now, we will use the unitary method to calculate the amount of carbon needed to produce 270 kg of aluminium.

Carbon needed to produce 270kg Aluminium = ${\dfrac{36}{108}}\times 270$ = 89.99kg $\approx$ 90kg

Hence, the mass of carbon required to produce 270 kg of aluminium is 90 kg.

Note: The carbon reduction method is not used to extract aluminium from its ores because the temperature required is too high for the reaction which is not economical. Hence, the electrolysis process (Hall-Heroult process) is used in extraction of aluminium.