Problem 78 - A Complete Resource Book in Chemistry for JEE Main

Question

The number of chloride ions produced by the complex tetraamminechloroplatinum(IV) chloride in an aqueous solution is (a) 1 (b) 2 (c) 3 (d) 4

Step-by-Step Solution

Answer

The number of chloride ions produced is 2, option (b).

Step 1: Understanding the Complex

Tetraamminechloroplatinum(IV) chloride is a coordination compound consisting of a central platinum ion (Pt) surrounded by four ammonia (ogonium) molecules and one chloride ion. Thus, its chemical formula can be represented as [Pt(NH₃)₄Cl]Cl₂.

Step 2: Coordination Sphere and External Ions

In the formula [Pt(NH₃)₄Cl]Cl₂, the coordination sphere [Pt(NH₃)₄Cl] contains the platinum, ammonia ligands, and one chloride ion. The two Cl⁻ ions outside the brackets are counterions.

Step 3: Determining Chloride Ions

In an aqueous solution, the complex dissociates, releasing two chloride ions from outside the coordination complex. The chloride within the coordination sphere remains bound to the platinum.

Key Concepts

Chloride Ions

Chloride ions, represented as Cl⁻, are a common type of ion found in many chemical reactions and compounds. In the context of coordination chemistry, chloride ions can play different roles. They may be part of the coordination sphere, acting as ligands, or they might exist as counterions outside the coordination compound.
When tetraamminechloroplatinum(IV) chloride dissolves in water, three chloride ions are initially linked with the structure: one within the coordination sphere and two as counterions. The latter two Cl⁻ can fully dissociate in an aqueous solution, which means they are released into the solution as free ions. This dissociation changes the composition and reactivity of the solution, particularly impacting conductivity and pH levels.
Therefore, in solutions, it's important to distinguish between the chloride ions that remain bound within the coordination sphere and those that become free ions. This affects the calculation of the total number of free chloride ions available for further reactions or interactions.

Coordination Sphere

In coordination chemistry, the coordination sphere is a crucial concept used to describe the spatial arrangement and interactions of a central metal ion with surrounding ligands. This system is often enclosed in square brackets, as in the case of \[[\text{Pt(NH}_3\text{)}_4\text{Cl}]\],indicating the chemical structure of the complex.
The coordination sphere includes the metal center, which in this case is platinum, and the attached molecules or ions (ligands) directly bonded to the metal. For tetraamminechloroplatinum(IV) chloride, the platinum ion is surrounded by four ammonia molecules and one chloride ion as its ligands.
Understanding this concept helps in identifying which parts of a complex will dissociate in solution. All components within the coordination sphere remain bound to the central metal ion, while any ions or molecules outside this sphere, such as counterions, can dissociate. Hence, a deep understanding of a coordination sphere allows chemists to predict the behavior of the compound in various environments, including aqueous solutions.

Aqueous Solution

An aqueous solution is a solution in which water is the solvent. This is a common medium for reactions in coordination chemistry because it allows for easy mixing and interaction of ions and molecules.
When a coordination compound like tetraamminechloroplatinum(IV) chloride is introduced into an aqueous solution, the solvent plays a key role in the dissociation process. Water molecules surround each ion or molecule, stabilizing them in solution. This process helps break the bonds between ions that exist outside the coordination sphere, like the counterions in this scenario.
Consequently, in an aqueous medium, the complex [Pt(NH₃)₄Cl] dissociates, releasing its counterions into the solution. Understanding aqueous solutions is crucial, as this environment affects the solubility, conductivity, and overall reactivity of chemical compounds. Being proficient in how various molecules behave in water can offer insights into potential chemical reactions and product formation.