Match each redox reaction scenario involving an oxidizing or reducing agent on the left wi… — JAMB UTME

Match each redox reaction scenario involving an oxidizing or reducing agent on the left with its corresponding characteristic laboratory observation on the right.

Bubbling sulfur(IV) oxide ( $SO_2$ ) gas into acidified potassium tetraoxomanganate(VII) ( $KMnO_4$ ) solutionThe purple solution turns colorless as $MnO_4^-$ ions are reduced to $Mn^{2+}$ ions.
Passing chlorine ( $Cl_2$ ) gas into aqueous potassium iodide ( $KI$ ) solutionThe colorless solution turns brown due to the oxidation of $I^-$ ions to liberated $I_2$ .
Adding concentrated trioxonitrate(V) acid ( $HNO_3$ ) to freshly prepared iron(II) tetraoxosulfate(VI) ( $FeSO_4$ ) solutionThe pale green solution turns reddish-brown due to the oxidation of $Fe^{2+}$ to $Fe^{3+}$ ions.
Bubbling hydrogen sulfide ( $H_2S$ ) gas through iron(III) chloride ( $FeCl_3$ ) solutionThe yellow/brown solution turns pale green accompanied by the deposit of yellow elemental sulfur.

Answer

The correct pairings match each redox reagent with its specific electron-transfer observation:

SO_2

with acidified

KMnO_4

produces a purple to colorless change;

Cl_2

with aqueous

KI

turns colorless solution brown; conc.

HNO_3

with

FeSO_4

converts pale green solution to brown; and

H_2S

with

FeCl_3

converts yellow/brown solution to pale green with yellow sulfur deposit.

Each pair correctly links the specific chemical species undergoing oxidation or reduction to its empirical qualitative test result. Sulfur(IV) oxide decolorizes acidified potassium tetraoxomanganate(VII); chlorine oxidizes iodide ions to brown iodine; concentrated trioxonitrate(V) acid converts green iron(II) to brown iron(III); and hydrogen sulfide reduces brown iron(III) to green iron(II) with yellow sulfur precipitation.

Step-by-Step Solution

Analyze the redox roles of the reagents in each left item.

SO_2

and

H_2S

act as reducing agents;

Cl_2

and conc.

HNO_3

act as oxidizing agents.

Identifying whether a species donates or accepts electrons determines the expected chemical transformation of the target solution.

Determine the oxidation state change and color change for

SO_2

+ acidified

KMnO_4

MnO_4^-

(oxidation state +7, purple) is reduced to

Mn^{2+}

(oxidation state +2, colorless).

Manganate(VII) reduction is the standard test for reducing agents like

SO_2

Determine the oxidation state change and color change for

Cl_2

+ aqueous

KI

I^-

(oxidation state -1, colorless) is oxidized to

I_2

(oxidation state 0, brown).

Halogen displacement shows chlorine's higher electronegativity and oxidizing strength compared to iodine.

Determine the oxidation state change for conc.

HNO_3

FeSO_4

and

H_2S

FeCl_3

Conc.

HNO_3

oxidizes pale green

Fe^{2+}

to brown

Fe^{3+}

H_2S

reduces yellow/brown

Fe^{3+}

to pale green

Fe^{2+}

with precipitate of sulfur.

Iron transitions between +2 (pale green) and +3 (yellow/brown) depending on whether an oxidant or reductant is introduced.

Key Concept

Laboratory identification of oxidizing and reducing agents via characteristic color changes and oxidation state transitions

Estimated Time:2m 0s

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