Question

Which statement is incorrect regarding Hall-Heroult process for metallurgy of aluminum?
1. Use of $Na _{3} Al F _{6}$ lowers the melting point of $Al _{2} O _{3}$
2. Steel vessel with lining of carbon acts as cathode
3. Graphite is used as anode
4. Carbon dioxide gas is generated at cathode

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (D)

In Hall-Heroult process for extraction of aluminium (crude) from alumina $\left( Al _{2} O _{3}\right)$. Statements $(1), (2)$ and $(3)$ are correct because cryolite $\left( Na _{3} AlF _{6}\right)$ is added to $Al _{2} O _{3}$ to lower, its melting point. Here, steel vessel with lining of carbon acts as cathode and graphite acts as anode, but statement $(4)$ is incorrect because $A l$ gets deposited at cathode.