Question

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

• A. $CO$ and $CO_2$ are produced in this process
• B. $Al_2O_3$ 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. $Na_3AlF_6$ serves as the electrolyte

Answer 1

The Correct Option is D

The Hall-Heroult process is used for the extraction of aluminum from its oxide, Al_2O_3 (alumina). Let's evaluate each statement:

1. CO and CO_2 are produced in this process.

   In the Hall-Heroult process, carbon anodes are used, and during the electrolysis, these anodes get oxidized, producing carbon dioxide (CO_2). Carbon monoxide (CO) can also be produced in smaller amounts. Therefore, this statement is correct.

2. Al_2O_3 is mixed with CaF_2 which lowers the melting point of the mixture and brings conductivity.

   In the Hall-Heroult process, Al_2O_3 is indeed mixed with cryolite (Na_3AlF_6) and calcium fluoride (CaF_2), which lowers the melting point and increases conductivity. Thus, this statement is correct.

3. Al^{3+} is reduced at the cathode to form Al.

   During the electrolysis process, Al^{3+} ions are reduced at the cathode to form aluminum metal. This statement is correct.

4. Na_3AlF_6 serves as the electrolyte.

   Na_3AlF_6 (cryolite) serves as a solvent or a flux, not solely as the electrolyte. The electrolyte in the Hall-Heroult process is primarily molten alumina dissolved in molten cryolite. Thus, this statement is incorrect and is the false statement among the options.

Therefore, the false statement regarding the Hall-Heroult process is: Na_3AlF_6 serves as the electrolyte.