JEE Challenger
More from General Principles and Processes of Isolation of Elements
ChemEasyAdv 2011 • Paper 2

Oxidation States of Iron in Haematite and Magnetite

Oxidation states of the metal in the minerals haematite and magnetite, respectively, are

Options

A

II, III in haematite and III in magnetite

B

II, III in haematite and II in magnetite

C

II in haematite and II, III in magnetite

D

III in haematite and II, III in magnetite

Correct

Topics & Concepts

General Principles and Processes of Isolation of ElementsMetallurgyOxidation State

Step-by-Step Solution

To determine the oxidation states of iron in the minerals haematite and magnetite:

  1. Haematite:

    • The chemical formula of haematite is Fe2O3\mathrm{Fe}_2\mathrm{O}_3.
    • Oxygen typically has an oxidation state of −2-2.
    • Let the oxidation state of iron (Fe\mathrm{Fe}) in haematite be xx.
    • Applying the rule of electroneutrality for the compound:
      2x+3(−2)=02x + 3(-2) = 0
      2x−6=0  ⟹  x=+3 (or III)2x - 6 = 0 \implies x = +3 \text{ (or } \mathrm{III}\text{)}
    • Thus, iron is present solely in the III\mathrm{III} oxidation state in haematite.

  2. Magnetite:

    • The chemical formula of magnetite is Fe3O4\mathrm{Fe}_3\mathrm{O}_4.
    • Magnetite is a mixed oxide composed of iron(II) oxide and iron(III) oxide in a 1:11:1 stoichiometric ratio:
      Fe3O4≡FeO⋅Fe2O3\mathrm{Fe}_3\mathrm{O}_4 \equiv \mathrm{FeO} \cdot \mathrm{Fe}_2\mathrm{O}_3
    • In FeO\mathrm{FeO}:
      x+(−2)=0  ⟹  x=+2 (or II)x + (-2) = 0 \implies x = +2 \text{ (or } \mathrm{II}\text{)}
    • In Fe2O3\mathrm{Fe}_2\mathrm{O}_3:
      2x+3(−2)=0  ⟹  x=+3 (or III)2x + 3(-2) = 0 \implies x = +3 \text{ (or } \mathrm{III}\text{)}
    • Consequently, each formula unit of magnetite contains one Fe2+\mathrm{Fe}^{2+} ion and two Fe3+\mathrm{Fe}^{3+} ions. Therefore, iron exhibits both II\mathrm{II} and III\mathrm{III} oxidation states in magnetite.

Hence, the oxidation states of the metal in haematite and magnetite are III\mathrm{III} and II,III\mathrm{II, III}, respectively.

Correct Option: (D)

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