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Difficulty: HardSulfur Allotropes, Hydrogen Sulfide, and Sulfur(IV) Oxide

Complete the following passage regarding the redox behavior of hydrogen sulfide gas when reacted with an iron(III) compound by filling in the blanks with the correct chemical terms.

Answer:When hydrogen sulfide gas is bubbled through an acidified solution of iron(III) chloride, the characteristic yellow color of the solution changes to 【green】 due to the reduction of iron(III) ions to iron(II) ions, while a fine 【yellow】 precipitate of elemental sulfur is deposited.

Answer

The solution turns pale green (or green) due to the formation of iron(II) ions (Fe2+Fe^{2+}), accompanied by the deposition of a yellow precipitate of elemental sulfur (SS).
Hydrogen sulfide gas (H2SH_2S) acts as a strong reducing agent. When passed into an acidified solution of iron(III) chloride (FeCl3FeCl_3), it reduces yellow Fe3+Fe^{3+} ions to light green Fe2+Fe^{2+} ions, while H2SH_2S itself gets oxidized to form a yellow precipitate of elemental sulfur (SS). The overall ionic equation for the reaction is: 2Fe(aq)3++H2S(g)→2Fe(aq)2++2H(aq)++S(s)2Fe^{3+}_{(aq)} + H_2S_{(g)} \rightarrow 2Fe^{2+}_{(aq)} + 2H^+_{(aq)} + S_{(s)}.

Step-by-Step Solution

1
Identify the role of hydrogen sulfide (H2SH_2S) in the reaction.
H2SH_2S acts as a reducing agent in acidic solution.
Sulfur in H2SH_2S has an oxidation state of −2-2 and undergoes oxidation to elemental sulfur (00 oxidation state).
2
Determine the change in oxidation state of iron.
Iron(III) ions (Fe3+Fe^{3+}) are reduced to iron(II) ions (Fe2+Fe^{2+}).
Iron(III) chloride solution is yellow/brown due to Fe(aq)3+Fe^{3+}_{(aq)}, whereas iron(II) ions (Fe(aq)2+Fe^{2+}_{(aq)}) impart a light green/pale green color to the aqueous solution.
3
Identify the physical appearance of oxidized sulfur product.
Elemental sulfur precipitates out of the solution.
Insoluble sulfur particles form a yellow suspension or precipitate in the solution.

Key Concept

Reducing property of Hydrogen Sulfide (H2SH_2S)
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Topics

Sulfur Allotropes, Hydrogen Sulfide, and Sulfur(IV) Oxide

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