.What are the original and final oxidation numbers for iron in the smelting of iron from iron oxide? Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g)
The Correct Answer and Explanation is:
Correct Answer:
In the smelting of iron from iron oxide:
- Original oxidation number of iron (Fe) in Fe₂O₃ is +3
- Final oxidation number of iron (Fe) in Fe (metal) is 0
Explanation:
In the chemical reaction:
Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g)
iron is being extracted from its ore, iron(III) oxide (Fe₂O₃), using carbon monoxide (CO) as a reducing agent. To determine the oxidation states, we look at each element in the compounds involved.
Fe₂O₃ is a neutral compound. Oxygen almost always has an oxidation number of −2 in compounds. Since there are three oxygen atoms, their total contribution to the charge is 3 × (−2) = −6. To balance this, the two iron atoms must contribute +6, so each iron atom has an oxidation number of +3.
Thus, in Fe₂O₃, iron has an oxidation number of +3.
On the product side, Fe appears as a pure element. Elements in their elemental form have an oxidation number of 0. This means iron has been reduced — its oxidation number has decreased from +3 to 0.
This decrease shows that iron gains electrons. Specifically, each Fe³⁺ ion gains 3 electrons to become Fe⁰:
Fe³⁺ + 3e⁻ → Fe
At the same time, CO is oxidized to CO₂. Carbon in CO typically has an oxidation number of +2, and in CO₂ it becomes +4, indicating it loses electrons.
This reaction is an example of a redox (reduction–oxidation) process:
- Iron is reduced (gain of electrons, +3 to 0)
- Carbon monoxide is oxidized (loss of electrons, +2 to +4)
The reduction of iron oxide to metallic iron is the key step in iron smelting, where iron is separated from its ore for industrial use.
