2002 AIPMT The p-Block ElementsOxidising power of halogens Easy Question 2 of 2 in Oxidising power of halogens

Which reaction is not feasible : -

A $2KI + Br_2 \rightarrow 2KBr + I_2$
B $2KBr + I_2 \rightarrow 2KI + Br_2$
C $2KBr + Cl_2 \rightarrow 2KCl + Br_2$
D $2H_2O + 2F_2 \rightarrow 4HF + O_2$

The answer is B.

Solution

The oxidising power of halogens decreases down the group: $F_2 \gt Cl_2 \gt Br_2 \gt I_2$.
A halogen can displace (oxidise) a halide ion of a halogen below it in the group.
$Br_2$ oxidises $I^-$ to $I_2$: feasible. $Cl_2$ oxidises $Br^-$ to $Br_2$: feasible. $F_2$ oxidises water to $O_2$: feasible.
$I_2$ is a weaker oxidising agent than $Br_2$, so it cannot oxidise $Br^-$ to $Br_2$.
So the reaction $2KBr + I_2 \rightarrow 2KI + Br_2$ is not feasible.

Concept Displacement reactions of halogens

Oxidising power of halogens in past papers

2 questions from this chapter have appeared across 2 exam years.