Question at position 16 Which substance serves as the oxidizing agent in the following reaction? I2(s) + 2Fe2+(aq) → 2I−(aq) + 2Fe3+(aq) Fe3+(aq) Fe2+(aq)I2(s)I−(aq)单项选择题
A
Fe3+(aq)
B
Fe2+(aq)
C
I2(s)
D
I−(aq)

Question

Question at position 16 Which substance serves as the oxidizing agent in the following reaction? I2(s) + 2Fe2+(aq) → 2I−(aq) + 2Fe3+(aq) Fe3+(aq) Fe2+(aq)I2(s)I−(aq)

BlackTom AI · Accepted Answer

An oxidizing agent is a species that gains electrons (is reduced) during a reaction.

1) Relevant concepts
- Oxidation: loss of electrons; reduction: gain of electrons.
- Oxidizing agent: the reactant that is reduced (accepts electrons).
- Assigning oxidation states to identify electron transfer.

2) Step-by-step reasoning with oxidation states
- I2(s): each iodine atom in elemental I2 has oxidation state 0.
- I−(aq): iodine in iodide has oxidation state −1.
- Fe2+(aq): iron has oxidation state +2.
- Fe3+(aq): iron has oxidation state +3.
Comparing reactants to products shows how oxidation states change.

3) Electron transfer (showing intermediate steps)
Write half-reactions with electrons:
- Reduction half-reaction (iodine): I2 + 2 e− → 2 I−
  (I: 0 → −1, each iodine gains 1 e−; total 2 e− gained per I2)
- Oxidation half-reaction (iron): 2 Fe2+ → 2 Fe3+ + 2 e−
  (Fe: +2 → +3, each Fe2+ loses 1 e−; two Fe2+ lose 2 e− total)
Combine the half-reactions: electrons cancel, yielding the overall equation given.

4) Why the correct answer is correct
I2 is reduced (0 → −1) by accepting the 2 electrons released when two Fe2+ ions are oxidized. Because I2 gains electrons, it is the oxidizing agent — it causes iron to be oxidized by taking electrons from it.

5) Why the other choices are incorrect
- Fe3+(aq): this is a product already oxidized (+3); it cannot be the oxidizing agent here because it does not accept electrons in this reaction.
- Fe2+(aq): this species is oxidized (loses electrons) and therefore is the reducing agent, not the oxidizing agent.
- I−(aq): this is the reduced product (already gained electrons), so it is not the oxidizing agent in the reaction; it cannot accept more electrons in this context.

6) Conclusion
I2(s) is the oxidizing agent, which matches the provided correct answer: I2(s).

Question at position 16 Which substance serves as the oxidizing agent in the following reaction? I2(s) + 2Fe2+(aq) → 2I−(aq) + 2Fe3+(aq) Fe3+(aq) Fe2+(aq)I2(s)I−(aq)单项选择题

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