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Difficulty: HardDefinitions and Classical vs Modern Concepts of Redox
The transformation of iron(II) ions to iron(III) ions in aqueous solution is represented by the ionic half-equation:
Fe(aq)2+→Fe(aq)3++e−\text{Fe}^{2+}_{(aq)} \rightarrow \text{Fe}^{3+}_{(aq)} + e^-
Which of the following statements correctly explains this chemical change in terms of classical and modern redox concepts?
  1. It is an oxidation process because iron(II) loses an electron, resulting in an increase in oxidation state from +2+2 to +3+3, which expands beyond classical oxygen-addition definitions.Answer
  2. B
    It is a reduction process because iron(II) loses a negatively charged electron, which decreases its net oxidation state.
  3. C
    It is an oxidation process because uncombined elemental iron must be formed with a non-zero oxidation state before becoming iron(III).
  4. D
    It is a reduction process because classical redox definitions require the addition of oxygen atoms for any oxidation to take place.

Answer

The transformation is an oxidation process because iron(II) loses an electron, resulting in an increase in its oxidation number from +2+2 to +3+3.
The correct option accurately applies the modern definition of redox. Loss of electrons (e−e^-) increases the charge/oxidation state of iron from +2+2 to +3+3, which defines oxidation regardless of whether oxygen is present.

Step-by-Step Solution

1
Analyze the given ionic half-equation
Iron(II) ion (Fe2+\text{Fe}^{2+}) releases one electron (e−e^-) to become iron(III) ion (Fe3+\text{Fe}^{3+}).
Determining electron movement is key to applying modern redox definitions.
2
Apply modern redox definitions (electron transfer and oxidation number)
Loss of electrons corresponds to oxidation. The oxidation number increases from +2+2 to +3+3.
By definition, oxidation is loss of electrons (OIL) and increase in oxidation state.
3
Compare with classical redox definitions
Classical definitions restricted oxidation to oxygen gain or hydrogen loss, whereas modern electron theory accounts for ion conversions without oxygen.
Modern definitions generalize redox behavior to non-oxygen reactions.

Key Concept

Modern vs Classical Redox Concepts: Oxidation as Electron Loss and Oxidation State Increase
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Topics

Definitions and Classical vs Modern Concepts of Redox

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