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Difficulty: MediumOxidizing and Reducing Agents and Tests

In the redox reaction represented by the equation H2S(g)+Cl2(g)→2HCl(g)+S(s)H_2S_{(g)} + Cl_{2(g)} \rightarrow 2HCl_{(g)} + S_{(s)}, which substance acts as the reducing agent?

  1. H2SH_2S, because sulfur increases its oxidation state from −2-2 to 00Answer
  2. B
    Cl2Cl_2, because chlorine decreases its oxidation state from 00 to −1-1
  3. C
    H2SH_2S, because hydrogen is reduced from +1+1 to 00
  4. D
    Cl2Cl_2, because it loses electrons to form HClHCl

Answer

Hydrogen sulfide (H2SH_2S) is the reducing agent because sulfur is oxidized, increasing its oxidation number from −2-2 in H2SH_2S to 00 in elemental SS.
Hydrogen sulfide (H2SH_2S) acts as the reducing agent because sulfur undergoes oxidation. Its oxidation number increases from −2-2 in H2SH_2S to 00 in elemental sulfur (SS), indicating that it loses electrons to reduce chlorine.

Step-by-Step Solution

1
Assign oxidation numbers to each element in the given reaction.
In H2SH_2S: H=+1,S=−2H = +1, S = -2. In Cl2Cl_2: Cl=0Cl = 0. In HClHCl: H=+1,Cl=−1H = +1, Cl = -1. In elemental SS: S=0S = 0.
Determining oxidation states allows tracking of electron loss and gain.
2
Identify which species loses electrons (is oxidized).
Sulfur changes from −2-2 to 00, representing an increase in oxidation number (loss of electrons).
The reactant containing the element that undergoes oxidation is the reducing agent.

Key Concept

Oxidizing and Reducing Agents via Oxidation State Tracking
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Topics

Oxidizing and Reducing Agents and Tests

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