In the extraction of \(Al\) metal from Bauxite ore, the correct sequence of various processes involved is:
- Heating the ore to remove volatile impurities
- Electrolysis of molten ore-mixture
- Leaching of aluminium with concentrated \(NaOH\)
- Grading and crushing of big ore particles
- Mixing alumina with \(CaF_2\) or \(Na_3AlF_6\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → D, C, A, E, B
Aluminium is extracted from bauxite by concentration (Bayer’s process), conversion to pure alumina and electrolytic reduction (Hall–Héroult process).
D. Grading and crushing of big ore particles — first. The ore is broken into small pieces before any chemical treatment.
C. Leaching of aluminium with concentrated NaOH — second. \( \ce{Al2O3} \) dissolves as sodium aluminate and the impurities are left behind; the solution is then neutralised with \( \ce{CO2} \) to give hydrated alumina.
\( \ce{Al2O3(s) + 2NaOH(aq) + 3H2O(l) -> 2Na[Al(OH)4](aq)} \)
\( \ce{2Na[Al(OH)4](aq) + CO2(g) -> Al2O3.xH2O(s) + 2NaHCO3(aq)} \)
A. Heating the ore to remove volatile impurities — third. Heating the hydrated alumina drives off water and gives pure \( \ce{Al2O3} \).
\( \ce{Al2O3.xH2O(s)} \xrightarrow{1470\ \text{K}} \ce{Al2O3(s) + xH2O(g)} \)
E. Mixing alumina with CaF2 or Na3AlF6 — fourth. Cryolite and fluorspar lower the melting point of the mixture and increase its conductivity.
B. Electrolysis of molten ore-mixture — last. Aluminium is set free at the cathode and oxygen at the anode, which burns the carbon anode.
\( \ce{2Al2O3 + 3C -> 4Al + 3CO2} \)
Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.