Under standard conditions in acid solution, which of the following oxidising couples can oxidise Br- and I- but not Cl-? Use E deg(Cl2/Cl-) = 1.36 V, E deg(Br2/Br-) = 1.09 V, E deg(I2/I-) = 0.54 V.

JEE Advanced levelSingle correct optionDifficulty 3 of 3ph037

Under standard conditions in acid solution, which of the following oxidising couples can oxidise $Br X^{-}$ and $I X^{-}$ but not $Cl X^{-}$ ? Use $E^{\circ} (Cl X_{2} / Cl X^{-}) = 1.36$ V, $E^{\circ} (Br X_{2} / Br X^{-}) = 1.09$ V, $E^{\circ} (I X_{2} / I X^{-}) = 0.54$ V.

An oxidant must have a higher

E^{\circ}

than the halogen couple it oxidises.

1.33 > 1.09

and

1.33 > 0.54

but

1.33 < 1.36

, so dichromate oxidises

Br X^{-}

and

I X^{-}

only.

Fe X^{3 +}

and

Ag X^{+}

(0.77, 0.80 V) oxidise only

I X^{-}

, and permanganate (1.51 V) oxidises all three.