Problem 116 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following transformations: (1) \(\mathrm{XeF}_{6}+\mathrm{NaF}\) \(\rightarrow \mathrm{Na}^{+}\left[\mathrm{XeF}_{7}\right]^{-}\) (2) \(2 \mathrm{PCl}_{5}(\mathrm{~s}) \longrightarrow\left[\mathrm{PCl}_{4}\right]^{+}\left[\mathrm{PCl}_{6}\right]\) (3) \(\left.\left[\mathrm{Al}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}+\mathrm{H}_{2} \mathrm{O} \longrightarrow{[\mathrm{Al}}\left(\mathrm{H}_{2} \mathrm{O}\right)_{5} \mathrm{OH}\right]^{2+}+\mathrm{H}_{3} \mathrm{O}^{+}\) The possible transformations are (a) 1,2 and 3 (b) 1 and 3 only (c) 1 and 2 only (d) 2 only

Step-by-Step Solution

Answer

The possible transformations are (a) 1, 2, and 3.

Step 1: Evaluate Transformation 1

Transformation (1) involves \( \mathrm{XeF}_{6}+\mathrm{NaF} \rightarrow \mathrm{Na}^{+}\left[\mathrm{XeF}_{7}\right]^{-} \). This suggests the reaction forms a complex ion. \( \mathrm{XeF}_{6} \) acts as a Lewis acid accepting electrons from a fluoride ion forming \( \left[\mathrm{XeF}_{7}\right]^{-} \), indicating a successful Lewis acid-base reaction. Therefore, transformation (1) is valid.

Step 2: Evaluate Transformation 2

Transformation (2) involves \(2 \mathrm{PCl}_{5}(\mathrm{~s}) \longrightarrow\left[\mathrm{PCl}_{4}\right]^{+}\left[\mathrm{PCl}_{6}\right] \). In this reaction, \( \mathrm{PCl}_{5} \) dissociates into two ions \( \left[\mathrm{PCl}_{4}\right]^{+} \) and \( \left[\mathrm{PCl}_{6}\right]^{-} \). This represents a coordination complex and ion pair formation, making the reaction a valid transformation.

Step 3: Evaluate Transformation 3

Transformation (3) involves \( \left[\mathrm{Al}\left(\mathrm{H}_{2}\mathrm{O}\right)_{6}\right]^{3+}+\mathrm{H}_{2}\mathrm{O} \longrightarrow{[\mathrm{Al}}\left(\mathrm{H}_{2}\mathrm{O}\right)_{5}\mathrm{OH}\right]^{2+}+\mathrm{H}_{3}\mathrm{O}^{+} \). This shows a ligand substitution where one water molecule is replaced by a hydroxide ion and proton transfer to form \( \mathrm{H}_{3}\mathrm{O}^{+} \). This is a valid transformation as it includes a proton transfer and complex formation.

Step 4: Determine Valid Transformations

Based on the evaluations, transformations (1), (2), and (3) are all valid chemical processes. Thus the correct response to which transformations are possible is (a) 1, 2 and 3.

Key Concepts

Lewis Acid-Base Reactions

In chemistry, Lewis acid-base reactions are interactions where an electron pair is transferred from a base to an acid. A Lewis acid is a substance that can accept an electron pair, while a Lewis base donates an electron pair.
These reactions can form compounds called adducts. For example, in the first transformation involving \( \mathrm{XeF}_{6} + \mathrm{NaF} \rightarrow \mathrm{Na}^{+}\left[\mathrm{XeF}_{7}\right]^{-} \), \( \mathrm{XeF}_{6} \) acts as a Lewis acid by accepting an electron pair from fluoride \( \mathrm{F}^{-} \).
The result is the formation of the complex ion \( \left[\mathrm{XeF}_{7}\right]^{-} \), demonstrating a successful Lewis acid-base reaction. This illustrates how compounds can form through the simple movement of electron pairs, leading to new chemical structures.

Coordination Complexes

Coordination complexes are structures where a central atom, usually a metal, is surrounded by molecules or ions known as ligands. These ligands can donate electron pairs to the central atom, forming stable bonds.
In transformation (2), \(2 \mathrm{PCl}_{5}(\mathrm{s}) \longrightarrow\left[\mathrm{PCl}_{4}\right]^{+}\left[\mathrm{PCl}_{6}\right] \), \( \mathrm{PCl}_{5} \) acts as a coordination complex part by extending its coordination number upon forming ions.
Such a process leads to a stable ion pair formed by the dissociation of \( \mathrm{PCl}_{5} \) into \( \left[\mathrm{PCl}_{4}\right]^{+} \) and \( \left[\mathrm{PCl}_{6}\right]^{-} \). This type of reaction shows how coordination chemistry helps in understanding complex formation and stability.

Ligand Substitution

Ligand substitution occurs when one ligand in a complex is replaced by another. It is a common type of reaction in coordination chemistry.
The third transformation detail \( \left[\mathrm{Al}(\mathrm{H}_{2}\mathrm{O})_{6}\right]^{3+} + \mathrm{H}_{2}\mathrm{O} \rightarrow [\mathrm{Al}(\mathrm{H}_{2}\mathrm{O})_{5}\mathrm{OH}]^{2+} + \mathrm{H}_{3}\mathrm{O}^{+} \) illustrates this point.
Here, one of the water molecules \((\mathrm{H}_{2}\mathrm{O})\) acting as a ligand is replaced by a hydroxide ion \((\mathrm{OH}^{-})\). This substitution is crucial in the formation of new complexes and demonstrates the dynamic nature of chemical reactions involving metal centers and their surrounding ligands.

Proton Transfer

Proton transfer is a key process in many chemical reactions, especially in acid-base chemistry. It involves the movement of a proton \((\mathrm{H}^{+})\) from one molecule to another.
In transformation (3), proton transfer is seen where the reaction \( \left[\mathrm{Al}(\mathrm{H}_{2}\mathrm{O})_{6}\right]^{3+} + \mathrm{H}_{2}\mathrm{O} \rightarrow [\mathrm{Al}(\mathrm{H}_{2}\mathrm{O})_{5}\mathrm{OH}]^{2+} + \mathrm{H}_{3}\mathrm{O}^{+} \) results in the formation of \( \mathrm{H}_{3}\mathrm{O}^{+} \).
This happens as a proton from one of the \( \mathrm{H}_{2}\mathrm{O} \) molecules is transferred to another water molecule, converting it into a hydronium ion \( \mathrm{H}_{3}\mathrm{O}^{+} \). This process showcases how protons can be moved in solution, altering acidity.

Complex Ion Formation

Complex ion formation is a key principle in coordination chemistry where ions consisting of a central atom bonded to a set of surrounding ligands are formed. The process is important for the stability and solubility of different compounds.
In transform 1, the result is the complex ion \( \left[\mathrm{XeF}_{7}\right]^{-} \). Coordination of fluoride ions around \( \mathrm{Xe} \) enhances the stability of the entire ion.
Similarly, in transformation 3, the replacement of a water molecule in the \( \left[\mathrm{Al}(\mathrm{H}_{2}\mathrm{O})_{6}\right]^{3+} \) complex results in the formation of \( [\mathrm{Al}(\mathrm{H}_{2}\mathrm{O})_{5}\mathrm{OH}]^{2+} \).
Such complex ions play a crucial role in aqueous chemistry and industrial applications, highlighting the versatility and adaptation of chemical species to different conditions.