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

Fill in the missing chemical terms and oxidation numbers in the passage describing the reaction of hydrogen sulfide gas with an acidified oxidizing solution.

Answer:When hydrogen sulfide gas (H2S{\text{H}_2\text{S}}) is bubbled into an acidified solution of potassium tetraoxomanganate(VII), the purple solution is decolorized because H2S{\text{H}_2\text{S}} acts as a 【reducing】 agent. During this redox process, sulfur is oxidized from an oxidation state of 【-2】 in H2S{\text{H}_2\text{S}} to 【0】 in the yellow elemental precipitate formed.

Answer

The first blank is 'reducing', the second blank is '-2', and the third blank is '0'.
Hydrogen sulfide (H2S\text{H}_2\text{S}) acts as a strong reducing agent in aqueous chemical reactions. When reacted with acidified KMnO4\text{KMnO}_4, it reduces purple MnO4−\text{MnO}_4^- ions to colorless Mn2+\text{Mn}^{2+} ions, while sulfur itself is oxidized from an oxidation state of −2-2 to 00, forming a insoluble yellow precipitate of elemental sulfur.

Step-by-Step Solution

1
Determine the chemical role of H2S\text{H}_2\text{S} when reacting with acidified KMnO4\text{KMnO}_4.
Acidified KMnO4\text{KMnO}_4 is an oxidizing agent containing Mn7+\text{Mn}^{7+} (purple), which is reduced to Mn2+\text{Mn}^{2+} (colorless). Therefore, H2S\text{H}_2\text{S} acts as a reducing agent.
A substance that causes reduction in another species while undergoing oxidation itself is a reducing agent.
2
Calculate the oxidation state of sulfur in hydrogen sulfide (H2S\text{H}_2\text{S}).
With hydrogen in the +1+1 state (2×(+1)=+22 \times (+1) = +2), the oxidation number of sulfur must be −2-2 to make the neutral molecule sum to zero.
Sum of oxidation states in neutral compounds is zero.
3
Identify the oxidation state of sulfur in the elemental precipitate product.
Elemental sulfur (SS) has an oxidation state of 00.
The oxidation number of any uncombined element in its standard state is always zero.

Key Concept

Reducing properties of hydrogen sulfide gas and oxidation state changes in redox reactions
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Topics

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

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