Question

Which one of the following reactions does not occur?

• A. \(2H_2O(l)+2F_2(g)\rightarrow 4HF(aq)+O_2(g)\)
• B. \(2KF(aq)+Cl_2(g)\rightarrow 2KCl(aq)+F_2(g)\)
• C. \(2KBr(aq)+Cl_2(g)\rightarrow 2KCl(aq)+Br_2(l)\)
• D. \(2KI(aq)+Br_2(l)\rightarrow 2KBr(aq)+I_2(s)\)

Hint:

Remember the reactivity order of halogens: \[ F_2 \gt Cl_2 \gt Br_2 \gt I_2 \] A halogen can displace only the halide ions of elements below it in the group.

Answer 1

The Correct Option is B

Concept: The oxidizing power of halogens decreases down the group: \[\begin{aligned} F_2 \gt Cl_2 \gt Br_2 \gt I_2 \end{aligned}\] A more reactive halogen can displace a less reactive halide ion from its salt solution, but the reverse is not possible.

Step 1: Analyze the displacement order of halogens. \[ \begin{aligned} F_2 &:\quad \text{Highest oxidizing power} \\ Cl_2 &:\quad \text{High oxidizing power} \\ Br_2 &:\quad \text{Moderate oxidizing power} \\ I_2 &:\quad \text{Lowest oxidizing power} \end{aligned} \]

Step 2: Check each reaction. \[ \begin{aligned} (A) &:\; F_2 \text{ oxidizes water to oxygen} && (\text{Yes}) \\ (B) &:\; Cl_2 \text{ cannot oxidize } F^- \text{ to } F_2 && (\text{No}) \\ (C) &:\; Cl_2 \text{ displaces bromine from bromide} && (\text{Yes}) \\ (D) &:\; Br_2 \text{ displaces iodine from iodide} && (\text{Yes}) \end{aligned} \]

Step 3: Identify the reaction that does not occur. Since chlorine is less reactive than fluorine, \[\begin{aligned} Cl_2 \;\text{cannot oxidize}\; F^- \end{aligned}\] Therefore, \[\begin{aligned} \boxed{2KF(aq)+Cl_2(g)\rightarrow 2KCl(aq)+F_2(g)} \end{aligned}\] does not occur. Hence, option \(\mathbf{(B)}\) is correct.