Question

Considering Ellingham diagram, which of the following metals can be used to reduce alumina ?

• A. Cu
• B. Fe
• C. Mg
• D. Zn

Answer 1

The Correct Option is C

The Ellingham diagram is a graph that represents the temperature dependence of the standard free energy change for reactions, often for the extraction of metals from their ores. In metallurgy, it is frequently used to determine which reducing agent can be used to reduce a specific metal oxide.

The key concept of Ellingham's diagram is that a line lower on the diagram indicates a more stable compound, while a line with a more negative slope indicates the reaction is more spontaneous at higher temperatures.

In the case of reducing alumina (Al₂O₃), the reducing agent must form a more stable oxide than aluminum oxide. To decide which metal can be used as a reducing agent, we need to compare their positions on the Ellingham diagram:

1. Aluminum oxide’s stability: Aluminum oxide is typically represented by a horizontal line. The ores of aluminum are quite stable.
2. Magnesium (Mg): Magnesium is higher on the Ellingham diagram, meaning it forms magnesium oxide (MgO), which is more stable than alumina at most temperatures relevant for metallurgy. Thus, Mg can effectively reduce Al₂O₃.
3. Other Metals - Copper (Cu), Iron (Fe), Zinc (Zn): These metals are located lower than aluminum in the Ellingham diagram translating to lower stability of their oxides compared to alumina at relevant reaction temperatures. Hence, they cannot be employed to reduce Al₂O₃.

Therefore, the correct answer is that Magnesium (Mg) can be used to reduce alumina because it forms a more stable oxide than Al₂O₃.

In conclusion, based on Ellingham's diagram, Magnesium is the suitable reducing agent for alumina due to its position and oxide stability compared to alumina.