Complete the statement describing the redox reaction and observation when hydrogen sulfide… — JAMB UTME

Complete the statement describing the redox reaction and observation when hydrogen sulfide gas acts as a reducing agent with iron(III) chloride solution.

Answer:When hydrogen sulfide gas (

H_2S

) is bubbled through a reddish-brown aqueous solution of iron(III) chloride (

FeCl_3

), the solution changes color to 【green】 due to the reduction of

Fe^{3+}

Fe^{2+}

ions, while the hydrogen sulfide is oxidized to produce a yellow precipitate of elemental 【sulfur】.

Answer

The solution turns green (or pale green) due to the formation of

Fe^{2+}

ions, and a yellow precipitate of sulfur (or sulphur) is deposited.

In the chemical reaction

2Fe^{3+}_{(aq)} + H_2S_{(g)} \rightarrow 2Fe^{2+}_{(aq)} + S_{(s)} + 2H^{+}_{(aq)}

, iron(III) chloride acts as an oxidizing agent and is reduced to green iron(II) ions. Simultaneously, hydrogen sulfide acts as a reducing agent and is oxidized to elemental sulfur, which forms a yellow precipitate.

Step-by-Step Solution

Analyze the oxidation state changes in the reaction between

Fe^{3+}

ions and

H_2S

Iron is reduced from

+3

Fe^{3+}

+2

Fe^{2+}

. Sulfur is oxidized from

-2

H_2S

0

in elemental sulfur (

S

Iron(III) ions act as an oxidizing agent and undergo reduction, while hydrogen sulfide acts as a reducing agent and undergoes oxidation.

Relate the chemical species formed to their characteristic physical observations.

Aqueous

Fe^{3+}

ions (reddish-brown/yellow-brown) are converted into aqueous

Fe^{2+}

ions (green). The oxidation of hydrogen sulfide yields elemental sulfur, which appears as a pale yellow solid precipitate.

Observing distinct color changes and solid deposition is the primary laboratory method for identifying redox species.

Key Concept

Redox testing of hydrogen sulfide as a reducing agent with iron(III) salts

Estimated Time:1m 0s

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