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Difficulty: HardDefinitions and Classical vs Modern Concepts of Redox
Consider the conversion of iron(II) chloride to iron(III) chloride in aqueous solution: 2FeCl2(aq)+Cl2(g)→2FeCl3(aq)2\text{FeCl}_{2(aq)} + \text{Cl}_{2(g)} \rightarrow 2\text{FeCl}_{3(aq)} Which of the following statements correctly explains why the conversion of FeCl2\text{FeCl}_2 to FeCl3\text{FeCl}_3 is classified as an oxidation process under both classical and modern concepts of redox?
  1. Classically, iron(II) chloride gains an electronegative element (chlorine); modernly, the oxidation state of iron increases from +2 to +3 due to the loss of an electron.Answer
  2. B
    Classically, elemental chlorine undergoes oxidation because its oxidation number is +1; modernly, iron(II) ions gain electrons to form iron(III) ions.
  3. C
    Classically, iron(II) chloride loses oxygen to chlorine gas; modernly, chlorine gas is oxidized because it accepts two moles of electrons per mole of molecules.
  4. D
    Classically, the process represents an acid-base neutralization reaction; modernly, iron(II) chloride acts as a dehydrating agent by eliminating net positive charge.

Answer

The conversion of iron(II) chloride to iron(III) chloride is an oxidation process because classically, it involves the addition of an electronegative element (chlorine) to iron(II) chloride, and modernly, iron undergoes an increase in oxidation number from +2 to +3 via electron loss.
The correct answer accurately contrasts classical and modern definitions. Under classical rules, adding an electronegative element like chlorine to a compound constitutes oxidation. Under modern rules, oxidation is defined by electron loss and an increase in oxidation number, which occurs when iron(II) with an oxidation state of +2 loses an electron to become iron(III) with an oxidation state of +3.

Step-by-Step Solution

1
Analyze the reaction using classical redox definitions.
Classical redox extends beyond oxygen/hydrogen transfer: oxidation is defined as the addition of an electronegative element (such as chlorine) or removal of an electropositive element. In 2FeCl2+Cl2→2FeCl32\text{FeCl}_2 + \text{Cl}_2 \rightarrow 2\text{FeCl}_3, FeCl2\text{FeCl}_2 gains a chlorine atom (electronegative element), making it an oxidation process.
Classical definitions account for reactions not involving oxygen or hydrogen by tracking electronegative and electropositive additions/removals.
2
Analyze the reaction using modern electronic and oxidation state concepts.
The ionic half-reaction for iron is Fe2+→Fe3++e−\text{Fe}^{2+} \rightarrow \text{Fe}^{3+} + e^-. The oxidation state of iron increases from +2+2 in FeCl2\text{FeCl}_2 to +3+3 in FeCl3\text{FeCl}_3.
Modern theory defines oxidation as the loss of electrons (LEO) resulting in an increase in oxidation state.
3
Synthesize classical and modern findings to identify the correct statement.
The statement identifying chlorine addition as classical oxidation and Fe2+\text{Fe}^{2+} to Fe3+\text{Fe}^{3+} electron loss as modern oxidation is correct.
Both classical and modern frameworks independently confirm that FeCl2\text{FeCl}_2 undergoes oxidation.

Key Concept

Classical vs Modern Definitions of Oxidation and Reduction
Estimated Time:2m 0s
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Topics

Definitions and Classical vs Modern Concepts of Redox

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