Question

In the context of the Hall-Heroult process for the extraction of $\text{Al,}$ which of the following statements is false ?

• A. CO and $C O_{2}$ are produced in this process
• B. $Al_{2}O_{3}$ is mixed with $CaF_{2}$ which lowers the melting point of the mixture and brings conductivity
• C. $Al^{3 +}$ is reduced at the cathode to form Al
• D. $Na_{3}AlF_{6}$ helps in increasing the melting point of the mixture

Answer 1

Answer: (D)

Hall heroult process:

In the Hall-Héroult process the following simplified reactions take place at the carbon electrodes:

Cathode: $Al^{3 +}+3e^{- 1} \rightarrow Al$

Anode: $O^{2 -}+C \rightarrow CO+2e^{-} \, $

Overall:

$Al_{2}O_{3}+3C \rightarrow 2Al+3CO$

And $2 \, Al_{2}O_{3}+3C \rightarrow 4Al+3CO_{2}$

In reality, much more $CO_{2}$ is formed at the anode than $CO:$

Cryolite ( $Na_{3}AlF_{6}$ ) lowers the melting point of the mixture and make it more conductive in nature so as to carry out electrolysis of the ore in Hall-Heroult process.