Question

Given below are two statements: Statement (I): Oxidising power of halogens decreases in the order \[ F_2>Cl_2>Br_2>I_2 \] which is the basis of the “Layer test”. Statement (II): “Layer test” to identify \(Br_2\) and \(I_2\) in aqueous solution involves the oxidation of bromide or iodide into \(Br_2\) or \(I_2\) respectively with \(Cl_2\), which is a type of displacement redox reaction. In the light of the above statements, choose the correct answer:

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Oxidising power refers to the ability to accept electrons. A stronger oxidising agent can displace a weaker one from its salt solution. In the case of halogens, this trend follows their position in the periodic table and their standard reduction potentials.
Step 2: Detailed Explanation:
1. Analysis of Statement (I):
The standard reduction potentials (\(E^0\)) of halogens are: \(F_2 (+2.87V)>Cl_2 (+1.36V)>Br_2 (+1.09V)>I_2 (+0.54V)\).
Higher reduction potential means greater ease of reduction, hence stronger oxidising power.
The oxidising power correctly follows the order: \(F_2>Cl_2>Br_2>I_2\).
Statement (I) is True.

2. Analysis of Statement (II):
The "Layer Test" is used in qualitative analysis to identify Bromide (\(Br^-\)) and Iodide (\(I^-\)) ions.
Chlorine water (\(Cl_2\)) is added to the aqueous solution of the halide. Since \(Cl_2\) is a stronger oxidant than \(Br_2\) or \(I_2\), it oxidises the halides:
\(Cl_2 + 2Br^-(aq) \rightarrow 2Cl^-(aq) + Br_2\) (Orange/Brown layer in \(CHCl_3\) or \(CCl_4\)).
\(Cl_2 + 2I^-(aq) \rightarrow 2Cl^-(aq) + I_2\) (Violet/Purple layer in \(CHCl_3\) or \(CCl_4\)).
This is a redox displacement reaction where chlorine displaces bromine or iodine.
Statement (II) is True.
Step 3: Final Answer:
Both Statement I and Statement II are true.