JEE Main · 2021 · 16 Mar 2021 · Shift 2 · General Principles and Processes of Isolation of Metals

Which of the following reduction reaction CANNOT be carried out with coke?

(A) $Cu_{2} O \to Cu$
(B) $Fe_{2} O_{3} \to Fe$
(C) $ZnO \to Zn$
(D) $Al_{2} O_{3} \to Al$ ✓ Correct

Answer: (D)

Solution

Coke reduces an oxide only where carbon has the stronger pull on oxygen at the working temperature, that is where the carbon line of the Ellingham diagram lies below the line of the metal oxide. For copper(I) oxide, iron(III) oxide and zinc oxide that crossing is reached within the range of an ordinary furnace. Aluminium oxide is far more stable and its line stays below the carbon line until about 2000 degrees Celsius, where aluminium carbide forms in place of the metal, so aluminium is obtained instead by electrolysis of the molten oxide in cryolite. The reduction that cannot be carried out with coke is that of aluminium oxide to aluminium.

JEE Main · 2021 · 16 Mar 2021 · Shift 2 · Single correct option

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JEE Main · 2021 · 16 Mar 2021 · Shift 2 · General Principles and Processes of Isolation of Metals

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