Number of ions produced on electrolysis of [Co(NH3)6].Cl3, which gives 3 mol of AgCl on reacting with AgNO3, are:
4
Let's analyze the given coordination compound and determine the number of ions produced upon electrolysis. The compound is given as \([Co(NH_3)_6].Cl_3\).
Understanding Coordination Compounds and Ionization
Coordination compounds typically consist of a central metal atom or ion bonded to a set of ligands. These are enclosed in a square bracket, forming the coordination sphere. Any ions outside the coordination sphere are counterions. When a coordination compound dissolves in water, the coordination sphere usually remains intact, while the counterions dissociate.
Analyzing the Reaction with Silver Nitrate
The problem states that the compound reacts with silver nitrate (\(AgNO_3\)) to produce 3 moles of silver chloride (\(AgCl\)). Silver chloride is an insoluble precipitate. This reaction is a common test for free chloride ions (chloride ions that are not part of the coordination sphere).
The reaction is:
\(Cl^-(aq) + AgNO_3(aq) \rightarrow AgCl(s) + NO_3^-(aq)\)
Since 3 moles of \(AgCl\) are produced per mole of the coordination compound, it means that there are 3 moles of free chloride ions (\(Cl^-\)) available to react with \(AgNO_3\). These free chloride ions must be the counterions outside the coordination sphere.
Determining the Structure of the Complex
Given the formula \([Co(NH_3)_6].Cl_3\), and the information that there are three free chloride ions, the structure of the coordination compound in solution can be represented as:
\([Co(NH_3)_6]^{3+} \cdot 3Cl^-\)
Here, the species inside the square bracket, \([Co(NH_3)_6]^{3+}\), is the complex cation, and the three \(Cl^-\) ions are the counterions.
Dissociation on Electrolysis
Electrolysis of an ionic compound in solution involves the movement of its constituent ions towards the electrodes. For the compound \([Co(NH_3)_6]Cl_3\) in water, it dissociates into its ions.
The dissociation reaction is:
\([Co(NH_3)_6]Cl_3(aq) \rightarrow [Co(NH_3)_6]^{3+}(aq) + 3Cl^-(aq)\)
From this equation, we can see the types and number of ions produced:
- One complex cation: \([Co(NH_3)_6]^{3+}\)
- Three chloride anions: \(Cl^-\)
Calculating the Total Number of Ions
The total number of ions produced per formula unit of \([Co(NH_3)_6]Cl_3\) is the sum of the number of complex cations and the number of chloride anions.
Total ions = Number of complex cations + Number of chloride anions
Total ions = \(1 + 3 = 4\)
Therefore, 4 ions are produced on electrolysis of \([Co(NH_3)_6]Cl_3\).
Let's summarize the dissociation:
| Species | Charge | Number of Ions |
|---|---|---|
| \([Co(NH_3)_6]^{3+}\) | +3 | 1 |
| \(Cl^-\) | -1 | 3 |
Total number of ions = 1 (cation) + 3 (anions) = 4.
Revision Table: Coordination Chemistry Concepts
| Concept | Description | Example |
|---|---|---|
| Coordination Sphere | The central metal atom/ion and the ligands directly bonded to it, enclosed in square brackets. | \([Co(NH_3)_6]^{3+}\) in \([Co(NH_3)_6]Cl_3\) |
| Counterions | Ions outside the coordination sphere that balance the charge of the complex ion. Dissociate in solution. | \(Cl^-\) in \([Co(NH_3)_6]Cl_3\) |
| Ligand | Molecule or ion that binds to the central metal atom/ion. | \(NH_3\) in \([Co(NH_3)_6]Cl_3\) |
| Coordination Number | The number of ligands bonded to the central metal atom/ion. | 6 in \([Co(NH_3)_6]Cl_3\) (6 \(NH_3\) ligands) |
Additional Information on Complex Dissociation and Electrolysis
When a coordination compound dissolves in a solvent like water, it behaves like an electrolyte if it has counterions. The degree of ionization depends on the nature of the complex and the solvent. For simple salts like NaCl, they completely dissociate into \(Na^+\) and \(Cl^-\) ions. Coordination compounds with counterions also dissociate, separating the complex ion from the counterions.
The fact that \([Co(NH_3)_6].Cl_3\) gives 3 moles of AgCl with \(AgNO_3\) is direct evidence that all three chloride ions are outside the coordination sphere and behave as independent ions in solution. If a chloride ion were inside the coordination sphere, e.g., in a complex like \([Co(NH_3)_5Cl]Cl_2\), only 2 moles of AgCl would precipitate per mole of complex, because only the two external chloride ions would be available for reaction.
Electrolysis involves applying an electric current through the ionic solution. The positive ions (cations, like \([Co(NH_3)_6]^{3+}\)) move towards the negative electrode (cathode), and the negative ions (anions, like \(Cl^-\)) move towards the positive electrode (anode). The number of ions in solution determines the electrical conductivity of the solution; a higher concentration of ions leads to higher conductivity (assuming similar charge and mobility).
In this specific case, the dissolution and subsequent electrolysis of \([Co(NH_3)_6]Cl_3\) produces one triply charged cation and three singly charged anions, resulting in a total of four ions per formula unit.
Important Questions from Coordination Compounds
Match List-I with List-II:
List-I List-II (A) Diamagnetic solid (I) CrO₂ (B) Ferromagnetic solid (II) Fe₃O₄ (C) Antiferromagnetic solid (III) NaCl (D) Ferrimagnetic solid (IV) MnO Choose the correct answer from the options given below:
[NiCl₂(PPh₃)₂] is named as:
Inner orbital complex among the following is:
(A) [Co(NH₃)₆]³⁺
(B) [CoF₆]³⁻
(C) [Ni(CN)4]²⁻
(D) [MnCl₆]³⁻
(E) [FeF₆]³⁻
Choose the correct answer from the options given below:
Which will form the most stable complex?
How many Cr-O bonds in dichromate ions are of the same bond length and are in resonance?
