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Difficulty: HardOxidation Numbers and IUPAC Nomenclature of Redox Species

In the preparation of potassium ferrate, K2FeO4K_2FeO_4, elemental iron (FeFe) is oxidized in an alkaline medium. What is the change in the oxidation number of iron per atom during this reaction, and what is the systematic IUPAC name of K2FeO4K_2FeO_4?

  1. Increase of 6; potassium tetraoxoferrate(VI)Answer
  2. B
    Increase of 4; potassium tetraoxoferrate(VI)
  3. C
    Increase of 4; potassium tetraoxoferrate(IV)
  4. D
    Increase of 8; potassium tetraoxoferrate(VIII)

Answer

The oxidation number of iron increases by 6, and the systematic IUPAC name of K2FeO4K_2FeO_4 is potassium tetraoxoferrate(VI).
Free uncombined iron (FeFe) has an oxidation number of 00. In K2FeO4K_2FeO_4, potassium is +1+1 and oxygen is −2-2. Solving 2(+1)+Fe+4(−2)=02(+1) + Fe + 4(-2) = 0 yields Fe=+6Fe = +6. The change in oxidation number is +6−0=+6+6 - 0 = +6. The polyatomic anion FeO42−FeO_4^{2-} contains four oxo ligands attached to iron in the +6+6 oxidation state, making its systematic IUPAC name potassium tetraoxoferrate(VI).

Step-by-Step Solution

1
Determine the oxidation state of uncombined elemental iron (FeFe).
Oxidation state of Fe=0Fe = 0.
By IUPAC rules, elements in their free uncombined elemental state always have an oxidation number of zero.
2
Calculate the oxidation state of iron in K2FeO4K_2FeO_4.
Oxidation state of Fe=+6Fe = +6.
Potassium has an oxidation state of +1+1 and oxygen has −2-2. Setting up the charge balance equation: 2(+1)+Fe+4(−2)=0  ⟹  +2+Fe−8=0  ⟹  Fe=+62(+1) + Fe + 4(-2) = 0 \implies +2 + Fe - 8 = 0 \implies Fe = +6.
3
Calculate the change in oxidation number.
Change =+6−0=+6= +6 - 0 = +6 (an increase of 6).
The change in oxidation state is the final state minus the initial state.
4
Formulate the systematic IUPAC name for K2FeO4K_2FeO_4.
Potassium tetraoxoferrate(VI).
The salt consists of potassium cations and the polyatomic anion FeO42−FeO_4^{2-}. With four oxygen atoms surrounding iron in oxidation state +6+6, the IUPAC name is potassium tetraoxoferrate(VI).

Key Concept

Determination of oxidation state changes from elemental forms and IUPAC Stock nomenclature of oxoanions
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Topics

Oxidation Numbers and IUPAC Nomenclature of Redox Species

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