JEE Main · 2023 · Shift-ImediumDNF-008

Which halogen is known to cause the reaction given below? 2{MnO}_4^- + 2{X}^- 2{MnO}_4^{2-} + {X}_2

d & f-Block Elements · Class 12 · JEE Main Previous Year Question

Question

Which halogen is known to cause the reaction given below?

$2\text{MnO}_4^- + 2\text{X}^- \rightarrow 2\text{MnO}_4^{2-} + \text{X}_2$

Options

a
All halogens
b
Only Bromine
c
Only Iodine
✓
d
Only Chlorine

Correct Answerc

Only Iodine

Detailed Solution

Concept: Reducing power of halides

In this reaction, $\text{MnO}_4^-$ (+7) is reduced to $\text{MnO}_4^{2-}$ (+6), and $\text{X}^-$ is oxidised to $\text{X}_2$ .

For the reaction to proceed, the halide must be a stronger reducing agent than $\text{MnO}_4^{2-}/\text{MnO}_4^-$ .

Standard reduction potentials ( $E°$ ):

$\text{MnO}_4^-/\text{MnO}_4^{2-}$ : $+0.56$ V
$\text{I}_2/\text{I}^-$ : $+0.54$ V → $\text{I}^-$ can reduce $\text{MnO}_4^-$ ✓
$\text{Br}_2/\text{Br}^-$ : $+1.07$ V → $\text{Br}^-$ cannot ✗
$\text{Cl}_2/\text{Cl}^-$ : $+1.36$ V → $\text{Cl}^-$ cannot ✗

Reducing power: $\text{I}^- > \text{Br}^- > \text{Cl}^-$

Only $\text{I}^-$ is a strong enough reducing agent to convert permanganate to manganate.

Answer: Option (3) — Only Iodine

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