Match each redox reaction mixture (left) with its corresponding characteristic laboratory … — JAMB UTME

Match each redox reaction mixture (left) with its corresponding characteristic laboratory observation (right).

Acidified $KMnO_4(aq)$ mixed with sulfur(IV) oxide gas ( $SO_2$ )Purple solution is decolorized to form colorless $Mn^{2+}$ ions
Acidified $K_2Cr_2O_7(aq)$ treated with iron(II) tetraoxosulfate(VI) solution ( $FeSO_4$ )Solution turns from orange to green as $Cr^{3+}$ ions form
Chlorine gas ( $Cl_2$ ) bubbled through potassium iodide solution ( $KI$ )Solution turns brown due to liberated iodine ( $I_2$ )
Hydrogen sulfide gas ( $H_2S$ ) passed into iron(III) chloride solution ( $FeCl_3$ )Yellow-brown solution turns pale green with a yellow precipitate of sulfur

Answer

Acidified

KMnO_4

with

SO_2

changes from purple to colorless (

Mn^{2+}

); Acidified

K_2Cr_2O_7

with

FeSO_4

changes from orange to green (

Cr^{3+}

); Chlorine gas with

KI

forms brown iodine (

I_2

); Hydrogen sulfide gas with

FeCl_3

reduces

Fe^{3+}

Fe^{2+}

(pale green) with a yellow sulfur precipitate.

Each test pair matches an oxidizing or reducing reagent with its definitive qualitative laboratory test observation: permanganate decolorizes upon reduction, dichromate turns green upon reduction, iodide oxidizes to brown iodine, and iron(III) reduces to pale green iron(II) alongside yellow sulfur precipitation.

Step-by-Step Solution

Determine the redox behavior of

SO_2

with acidified

KMnO_4

SO_2

is oxidized while reducing purple

MnO_4^-

to colorless

Mn^{2+}

Potassium permanganate test for reducing agents involves reduction of manganese from oxidation state +7 to +2.

Determine the redox behavior of

FeSO_4

with acidified

K_2Cr_2O_7

Fe^{2+}

ions oxidize to

Fe^{3+}

while

Cr_2O_7^{2-}

(orange) is reduced to

Cr^{3+}

(green).

Dichromate(VI) is a standard oxidizing agent whose reduced form contains green chromium(III) ions.

Determine the reaction of

Cl_2

with

KI

Cl_2

oxidizes colorless

I^-

ions to elemental iodine (

I_2

), turning the solution brown.

Chlorine is a stronger oxidizing agent than iodine and displaces iodide from solution.

Determine the reaction of

H_2S

with

FeCl_3

H_2S

reduces yellow-brown

Fe^{3+}

to pale green

Fe^{2+}

while forming a insoluble yellow deposit of sulfur.

Hydrogen sulfide acts as a reducing agent and deposits elemental sulfur upon oxidation.

Key Concept

Laboratory tests and characteristic color changes for oxidizing and reducing agents.

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